邬磊^,1, 何志龙², 汤水荣³, 吴限², 张文菊¹, 胡荣桂^,21中国农业科学院农业资源与农业区划研究所,北京 100081
²华中农业大学资源与环境学院,武汉 430070
³海南大学热带作物学院,海口 570228

Greenhouse Gas Emission During the Initial Years After Rice Paddy Conversion to Vegetable Cultivation

WU Lei^,1, HE ZhiLong², TANG ShuiRong³, WU Xian², ZHANG WenJu¹, HU RongGui^{,2 1}Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081
²College of Recourses and Environment, Huazhong Agricultural University, Wuhan 430070
³College of Tropical Crops, Hainan University, Haikou 570228

通讯作者: 胡荣桂,E-mail： rghu@mail.hzau.edu.cn

责任编辑: 李云霞
收稿日期:2020-04-1接受日期:2020-06-3网络出版日期:2020-12-16

基金资助:

国家自然科学基金.41907093 中央公益性科研院所基本科研业务费专项.1610132019013

Received:2020-04-1Accepted:2020-06-3Online:2020-12-16
作者简介 About authors
邬磊,E-mail： wulei01@caas.cn。








摘要
【目的】近年来,随着我国社会经济的快速发展和人们生活水平的提高及膳食结构的改善,越来越多的稻田被转为蔬菜种植,影响了土壤碳氮转化过程及其引起的温室气体排放。因此有必要探究稻田转为蔬菜种植,特别是该土地利用方式转变初始阶段的温室气体（CH₄和N₂O）排放特征及其关键影响因素。【方法】试验选取了长期种植水稻的双季稻田,将其中一部分转为蔬菜种植,另一部分继续种植水稻,每个处理设置了3个重复,按照当地常规模式进行管理。采用静态暗箱—气相色谱法连续3年进行田间原位观测,比较分析稻田和由稻田转变的菜地CH₄和N₂O排放特征及其年际变化差异,明确稻田转为菜地初始阶段CH₄和N₂O排放的关键影响因素。【结果】稻田是重要的CH₄排放源,其第一年的排放强度（183.91 kg CH₄-C·hm^-2?a^-1）明显低于后续两年（241.56—371.50 kg CH₄-C·hm^-2?a^-1）,这主要归功于后两年降雨量的增加引起了土壤水分含量的升高。稻田转为菜地显著减少了CH₄排放,减少量相当于稻田CH₄年累积排放量的83%—100%。菜地第一年的CH₄累积排放量（31.22 kg CH₄-C·hm^-2）显著高于第二年（0.45 kg CH₄-C·hm^-2）和第三年（0.89 kg CH₄-C·hm^-2）,表明稻田转菜地对CH₄排放的影响具有时间滞后效应。稻田是弱的N₂O排放源（1.35—3.49 kg N₂O-N·hm^-2?a^-1）,其转为菜地显著增强了N₂O排放。菜地第一年的N₂O累积排放量（95.12 kg N₂O-N·hm^-2）显著高于第二年（38.28 kg N₂O-N?hm^-2）和第三年（40.07 kg N₂O-N·hm^-2）。菜地土壤异养呼吸对N₂O排放的影响在第一年明显高于第二、三年,表明稻田转为蔬菜种植的第一年,有机质矿化对N₂O排放有重要贡献。在100年尺度CO₂当量下,稻田转为蔬菜种植第一和第二年的综合增温潜势（GWP）相对于稻田分别显著增加了390%和98%,主要是由于增加的N₂O增温潜势超过了减少的CH₄增温潜势。但是,稻田转为菜地的第三年,菜地的GWP（(16.72±3.25) Mg CO₂-eq·hm^-2）与稻田（(14.84±1.39) Mg CO₂-eq·hm^-2）相比无显著差异,主要是由于减少的CH₄ 增温潜势完全抵消了增加的N₂O增温潜势。这些研究结果表明稻田转菜地对GWP的影响主要集中在该土地利用方式转变的第一年。【结论】稻田转为菜地显著减少了CH₄排放,增加了N₂O排放,增强了菜地第一和第二年的综合增温潜势。有机质矿化过程对新转菜地第一年较高的N₂O排放有重要贡献。这些研究结果表明了评价土地利用方式转变初始阶段温室气体排放特征的重要性,便于及时采取有效管理措施缓解温室气体排放,实现环境友好型农业可持续生产。
关键词： 稻田;菜地;土地利用方式;CH₄;N₂O;综合增温潜势

Abstract
【Objective】In recent years, with the rapid development of social economy, the improvement of people’s living standards and shifting diets and the increasing demands of vegetables result in a considerable share of rice paddy fields conversion to vegetable production in China, thus influencing soil carbon and nitrogen cycling and associated greenhouse gas (GHG) emissions. Therefore, it is necessary to investigate the impacts of land-use conversion from rice into vegetable cultivation on methane (CH₄) and nitrous oxide (N₂O) emissions and their key regulating factors, particularly during initial period upon conversion. 【Method】In this study, six rice paddies subjected to long-term double-rice planting were chosen, and the half of them were converted into vegetable cultivation (Veg) and the remaining still for rice production (Rice), with three replicates of each treatment. The Veg and Rice were managed according to local practices. The fluxes of CH₄ and N₂O from the rice paddy and converted vegetable fields were measured with static chambers from December 2012 to December 2015, so as to investigate the characteristics and inter-annual variation of CH₄ and N₂O emissions and to identify the key factors regulating the two GHGs during the initial period upon conversion. 【Result】Rice paddy acted as an important source of CH₄, and CH₄ emission was significantly lower in the first year (183.91 kg CH₄-C·hm^-2?a^-1) relative to the later two years (241.56-371.50 kg CH₄-C·hm^-2?a^-1), mainly attributed to enhanced precipitation increasing soil water content during the latter two years. Conversion from rice to vegetable cultivation substantially reduced CH₄ emission from Veg by 83%-100% as compared to Rice over the study period. Annual CH₄ emissions from Veg were significantly higher in the first year (31.22 kg CH₄-C·hm^-2) relative to any later years (0.45-0.89 kg CH₄-C·hm^-2), suggesting that this land-use conversion had strong legacy effect on CH₄ emission. Paddy soil acted as a minor source of N₂O (1.35-3.49 kg N₂O-N·hm^-2?a^-1). Rice conversion to vegetable cultivation led to substantial N₂O emission, particularly in the first year during which the cumulative emissions were significantly larger (95.12 kg N₂O-N·hm^-2) than that in the second (38.28 kg N·hm^-2) and third year (40.07 kg N₂O-N·hm^-2). N₂O fluxes from Veg were significantly and positively related to soil heterotrophic respiration rates (R_h), and the dependence of N₂O fluxes on R_h was greater in the first year relative to the subsequent two years. These results suggested that soil organic matter mineralization contributed to N₂O emissions during the first year upon land-use conversion from rice to vegetable production. Land-use conversion from rice to vegetable cultivation significantly increased the global warming potential (GWP) of Veg by 390% and 98% in the first and second year, respectively, relative to Rice, primarily due to the increased GWP of N₂O emission far outweighing the decreased GWP of CH₄ emission. In contrast, the GWP of rice (14.84±1.39 Mg CO₂-eq·hm^-2) was similar to that of Veg (16.72±3.25 Mg CO₂-eq·hm^-2) in the third year after conversion, due to the decreased GWP of CH₄ emission fully offsetting the increased GWP of N₂O emission. These results suggested that land-use conversion from rice to vegetable cultivation had significant impacts on the GWP only at the initial stage upon conversion. 【Conclusion】Land-use conversion from rice to vegetable cultivation significantly decreased CH₄ while increasing N₂O emissions over the whole study period, and increased the GWP only in the first and second year upon conversion. Soil organic matter mineralization significantly contributed to increased N₂O emission from the converted vegetable field. This study suggested that soil GHG emissions in the first years upon conversion were the most important, therefore, which should be considered when evaluating the environmental consequences of land-use conversion. This study also helped us develop effective options to alleviate the effects of land-use conversion on GHG emissions, and for sustainable agricultural production and GHG mitigation.
Keywords：rice paddy;vegetable field;land-use conversion;CH₄;N₂O;global warming potential (GWP)


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本文引用格式
邬磊, 何志龙, 汤水荣, 吴限, 张文菊, 胡荣桂. 稻田转为菜地初始阶段温室气体排放特征[J]. 中国农业科学, 2020, 53(24): 5050-5062 doi:10.3864/j.issn.0578-1752.2020.24.008
WU Lei, HE ZhiLong, TANG ShuiRong, WU Xian, ZHANG WenJu, HU RongGui. Greenhouse Gas Emission During the Initial Years After Rice Paddy Conversion to Vegetable Cultivation[J]. Scientia Acricultura Sinica, 2020, 53(24): 5050-5062 doi:10.3864/j.issn.0578-1752.2020.24.008


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0 引言

【研究意义】人类活动引起的大气中二氧化碳（CO₂）、甲烷（CH₄）和氧化亚氮（N₂O）等温室气体浓度的升高是造成全球气候变暖的主要原因之一^[1]。其中,CH₄和N₂O因其较高的增温潜势而备受关注。农业生产活动是重要的人为CH₄和N₂O排放源,其排放量占人类活动引起的CH₄和N₂O排放总量的56% ^[1],其中农业土地利用方式转变对温室气体排放存在重要影响^[2,3]。因此,有必要探究农业土地利用方式转变对温室气体排放的影响,这对减缓农业源温室气体排放具有重要意义。【前人研究进展】中国的水稻种植面积高达0.3亿hm²,约占全国耕地总面积的23% ^[4]。我国稻田CH₄和N₂O排放强度分别为4.8 Tg CH₄-C·a^-1和114.5 Gg N₂O-N·a^-1,是重要的温室气体排放源^[5]。近年来,随着社会经济的快速发展和人们膳食结构的改变,农业生产者为了追求较高的农产品收益,将大量稻田排水落干,转为玉米、蔬菜等旱地作物种植^[6,7,8]。这种农业土地利用方式转变会显著影响农田温室气体排放^[9,10]。NISHIMURA等^[10]2002年将一直种植水稻的淹水稻田改种旱作稻和大豆-小麦轮作,并对比研究2002—2004年间不同种植模式下温室气体排放差异,发现淹水稻田改为旱地作物种植显著降低了CH₄排放,而增强了N₂O排放。JIANG等^[11] 2002—2005在我国川中地区开展的田间观测试验表明,冬水田转为水旱轮作20年后显著减少了CH₄排放。稻-麦轮作和稻-油轮作的年CH₄排放量相对于冬水稻田分别降低了56%和59%;而N₂O年排放量提高了2—4倍。由此可见,农业土地利用方式的转变显著影响了CH₄和N₂O的排放。另外,农业土地利用方式转变也会对地表植被类型、土壤理化性质和微生物多样性等产生影响,从而影响土壤碳氮转化过程及其引起的温室气体排放特征^[12,13,14]。【本研究切入点】 目前,关于农业土地利用方式转变对温室气体排放影响的研究主要集中在转变多年达到稳定状态后的温室气体排放特征和规律^[11,15],而忽略了土地利用方式转变初始阶段的温室气体排放特征及综合温室效应。【拟解决的关键问题】本研究通过3年的田间观测试验,阐明稻田转为蔬菜种植初始阶段的CH₄和N₂O排放特征,明确不同转变年限下的综合温室效应。这对精确评估农业土地利用方式转变对温室气体排放的影响具有重要的参考意义。

1 材料与方法

1.1 研究区概括

本研究的试验区域位于湖南省长沙县金井镇脱甲村的中国科学院亚热带农业生态研究所长沙农业环境观测研究站内（28°32′46″ N, 113°19′50″ E,海拔80 m）。该区域近60年来的年均气温为17.5 °C,年降雨量为1 370 mm,降雨主要集中在每年的3-7月份。双季稻田面积占脱甲村区域总面积的27%。近年来,该区域有大量稻田排水、落干,转为蔬菜地。本研究选取的稻田土壤是由花岗岩风化形成的人为始成土^[16]。该水稻土有机碳含量为18.80 g?kg^-1,全氮2.10 g?kg^-1,全磷0.41 g?kg^-1,全钾0.29 g?kg^-1,pH为4.95。土壤砂粒、粉粒和黏粒分别占比27%、29%和44%。

1.2 试验设计

在研究区域选取了6块长期种植水稻的双季稻田（15 m×20 m,早稻-晚稻-休闲）。2012年7月将选取的稻田全部种上晚稻,10月底晚稻收获后,随机选取3块稻田排水、落干,并将其转为蔬菜地（Veg）,剩余的3块稻田（Rice）继续种植水稻并沿用之前的水稻田管理模式。每个处理设置3次重复。田间管理（包括肥料类型、施肥量和施肥时间、水分管理等）均采取当地的常规管理模式进行。试验期间,稻田和菜地施肥管理措施的详细信息参见表1。早稻和晚稻的磷、钾肥施入量相同：磷肥（过磷酸钙）40 kg P₂O₅·hm^-2,钾肥（氯化钾）100 kg K₂O·hm^-2,磷肥和钾肥作为基肥在水稻移栽前一次性施入。早稻和晚稻的水分管理模式一致：水稻秧苗（30 d生育期）移栽后,持续淹水一个月左右,排水晒田两周,然后间歇性灌溉维持到水稻收获前7—10 d,最后排水落干。

Table 1
表1
表1稻田和菜地施肥管理一览表
Table 1Overview of the fertilization practices of double-rice and vegetable fields during the observation period from 2012 to 2015

稻田 Rice paddy			菜地 Vegetable field
施肥时间 Fertilization date	肥料类型 Fertilizer type	施肥量 Rate (kg N·hm-2)	施肥时间 Fertilization date	肥料类型 Fertilizer types	施肥量 Rates (kg N·hm-2)
早稻 Early rice			红菜苔 Red cabbage
3 May 2013	尿素 Urea	60	8 Dec 2012	复合肥* Compound fertilizer	120
27 May 2013	尿素 Urea	36	2 Mar 2013	尿素 Urea	80
1 Jul 2013	尿素 Urea	24
			辣椒 Pepper
晚稻 Late rice			18 Apr 2013	复合肥 Compound fertilizer	90
14 Jul 2013	尿素 Urea	75	16 Jun 2013	尿素 Urea	60
1 Aug 2013	尿素 Urea	45
7 Sep 2013	尿素 Urea	30	白萝卜 Radish
			14 Sep 2013	复合肥 Compound fertilizer	120
早稻Early rice			11 Nov 2013	尿素 Urea	80
6 May 2014	尿素 Urea	60
17 May 2014	尿素 Urea	36	空心菜 Water spinach
27 Jun 2014	尿素 Urea	24	17 Apr 2014	复合肥 Compound fertilizer	80
			10 May 2014	尿素 Urea	50
晚稻Late rice			27 Jun 2014	尿素 Urea	50
24 Jul 2014	尿素 Urea	75	24 Aug 2014	尿素 Urea	20
31 Jul 2014	尿素 Urea	45
10 Sep 2014	尿素 Urea	30	白萝卜 Radish
			6 Sep 2014	复合肥 Compound fertilizer	120
早稻Early rice			30 Oct 2014	尿素 Urea	80
27 Apr 2015	尿素 Urea	60
6 May 2015	尿素 Urea	36	辣椒 Pepper
25 Jun 2015	尿素 Urea	24	16 Apr 2015	复合肥 Compound fertilizer	90
			15 Jul 2015	尿素 Urea	60
晚稻Late rice
20 Jul 2015	尿素 Urea	75	白萝卜 Radish
28 Jul 2015	尿素 Urea	45	2 Oct 2015	复合肥 Compound fertilizer	120
7 Sep 2015	尿素 Urea	30	29 Oct 2015	尿素 Urea	80
总氮用量 Total amount		810	总氮用量Total amount		1300

复合肥为 (NH₄)H₂PO₄和KCl的混合物（N﹕P₂O₅﹕K₂O = 15%﹕15%﹕15%）
Compound fertilizer is a mixture of (NH₄)H₂PO₄ and KCl, with N﹕P₂O₅﹕K₂O = 15%﹕15%﹕15%

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1.3 样品采集与测定

1.3.1 气体样品采集与测定 采用静态暗箱与气相色谱联用法采集测定气体样品。静态暗箱由底座（50 cm×50 cm×30 cm）、中箱（50 cm× 50 cm×50 cm）和顶箱（50 cm × 50 cm × 50 cm）三部分组成,均由不锈钢材质制成。底座上端安装有密封水槽,以便气体样品采集时阻止箱内与箱外气体交换;箱体用泡沫材料包裹,以便气体样品采集期间稳定箱内温度。箱体内部安装2个小风扇,用于混匀箱内气体。箱体侧面安有连接风扇的电源线、温度计探头接口和气体样品采集连接口。在每一块试验田中设置两个底座,其中一个底座中种有作物,而且底座内外作物密度一致,该底座主要用于测定CH₄和N₂O排放通量。另外一个底座置于作物行间（设置一块2 m × 2 m 不种作物的裸地）,用于测定CO₂排放通量（即异养呼吸速率,R_h）,用于表征土壤有机碳矿化速率。在整个作物生长周期,采样底座固定在同一处采样点。气体样品采集前,往底座的密封水槽中灌水,使采样箱与底座之间密封。气体样品采集时,将箱体平稳罩在底座上,用60 mL注射器通过三通阀连接采样箱,采集气体。在采样箱密闭后立即采集第一针气体样品,然后每隔10 min采集一次,每个采样点连续采集气体样品5次,采集时间为上午9：30—11：30。在气体样品采集的同时,测量箱内温度和土壤温度。气体样品采集完后,24 h内用气相色谱（安捷伦7890A）分析CO₂、CH₄和N₂O浓度。温室气体排放通量的观测时间段为2012年12月至2015年12月。一般情况下,气体样品采集频率为每周2次,但在施肥等田间管理期间,气体样品采集加密至每2天一次,持续一周。

1.3.2 土壤样品采集与测定 土壤样品的采集时间与气体样品采集保持一致,土壤样品每周采集一次,在施肥等田间管理期间每周采集两次。采集表层（0—20 cm）土壤,剔除可见凋落物和根系后,混均,装入自封袋,带回实验室,用于分析土壤理化性质。土壤质量含水量（SWC）采用烘干称重法测定^[17];土壤铵态氮和硝态氮采用K₂SO₄（0.5 mol·L^-1）溶液浸提（30 g土样添加80 mL浸提液）,流动注射分析仪测定;可溶性有机碳（DOC）浓度通过TOC自动分析仪测定;采用pH计测定土壤的pH^[17];SOC采用重铬酸钾容量法测定,土壤总氮（TN）使用硒粉-硫酸铜-硫酸消化法测定。土壤有机氮（SON）通过土壤总氮扣除矿质氮求得。

1.3.3 气象数据采集 降雨量和气温等气象数据通过观测研究站内的自动气象监测系统（Intelimet Advantage, Dynamax Inc.,USA;距离试验点80 m）获取（图1）。

图1

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图1观测期间降水和气温变化

Fig. 1Dynamics of precipitation and air temperature during the observation period

1.4 数据计算与统计

CO₂、CH₄和N₂O排放通量计算公式如下：

Flux=M/V₀×(H-h/100)×P/P₀×T/T₀×dc/dt

式中,M为待测气体相对分子质量（g·mol^-1）;V₀为标准状况下的摩尔体积（L·mol^-1）,在标准大气压下V₀ = 22.4 L·mol^-1;H为静态暗箱箱高（m）;h为稻田水深,P₀和T₀分别为标准大气压力（101.3 kPa）和标准大气温度（273 K）;P和T为气体样品采集时箱内的压力和气温（K）;dc/dt为气体样品采集期间箱内待测气体浓度（cm³·m^-3）随时间（h）变化的回归曲线斜率。

CH₄和N₂O累积排放量计算公式如下：

Ec=$\sum\limits_{i=1}^{n}{({{F}_{i}}+{{F}_{i+1}})/2}$×(t_i+1 - t_i) ×24

式中,Ec表示气体的累积排放量,n为观测次数,F_i和F_i+1为第i次和i+1次采样时目标气体的排放通量,t_i+1和t_i为第i+1次和i次的采样日期。

全球增温潜势（global warming potential（GWP）,Mg CO₂-equivalent·hm^-2）是表征温室气体对全球温室效应总影响的一个指标。该指标以给定时间尺度的CO₂质量当量计（CO₂-eq）。对于100 年时间尺度的气候变化,CO₂、CH₄和N₂O气体的GWP分别为1、28和265 ^[1]。

100 年时间尺度CH₄和N₂O综合增温潜势按下式计算：

GWP=F_CH4×16/12×28+F_N2O×44/28×265

式中,GWP单位为t·hm^-2（以CO₂-eq计）;F_CH4为CH₄的排放量（kgCH₄-C·hm^-2）;F_N2O为N₂O的排放量（kgN₂O-N·hm^-2）。

在方差分析前,所有的数据采用Shapiro-Wilk进行正态分布检验,不服从正态分布的数据通过对数转化以实现正态分布。采用单因素和多因素方差分析评价土地利用方式转变、年份及其交互作用对土壤理化指标（土壤有机碳、有机氮、容重、pH、温度、水分、可溶性有机碳和矿质态氮含量）、CH₄和N₂O累积排放量及GWP的影响。采用回归模型分析稻田和菜地CH₄和N₂O排放通量与土壤温度、水分、异养呼吸速率、可溶性有机碳和矿质态氮含量的关系,统计分析的显著性水平设定为P<0.05。使用SPSS软件进行数据统计分析（SPSS 20.0, SPSS Inc., IL, Chicago, USA）。采用Origin 8.0软件进行图形绘制。

2 结果

2.1 稻田和菜地土壤性质变化

稻田和菜地土壤性质在2012—2015年整个观测时间段及试验结束时都有所改变,且不同年份和处理间有差异（表2,图2）。2015年试验结束时菜地SOC、SON和pH与稻田相比均显著降低（P<0.05）,土壤容重显著增加（表 2）。在观测期间,稻田和菜地土壤温度变化趋势基本一致,随着季节更替而起伏变化（图2-a）,稻田土壤年平均温度显著高于菜地土壤（P<0.05,图2-b）。土壤质量含水量（SWC）也表现出季节性波动规律（图2-c）,主要受到降雨和灌溉的影响,除第一年稻田与菜地间SWC无显著差异外,第二和第三年稻田SWC均高于菜地（P<0.05,图2-d）。稻田土壤DOC含量在不同年份间无显著变化;而菜地土壤DOC含量呈现出增加的趋势（图2-e、2-f）。稻田和菜地土壤矿质氮（NH₄⁺-N和NO₃^--N）含量主要受施肥影响,施肥后稻田和菜地NH₄⁺-N含量及菜地NO₃^--N含量均有大幅度提升;而稻田NO₃^--N含量在整个观测期均处于较低水平,无明显的规律性（表 1,图2-g、2-h、2-i、2-j）。稻田土壤NH₄⁺-N年平均含量在年份间无显著差异;菜地NH₄⁺-N含量在第一年高于后续两年（P<0.05,图2-h）,菜地NO₃^--N含量在第一年低于后续两年（P<0.05,图2-j）。总体上,菜地NH₄⁺-N和NO₃^--N的3年平均含量均显著高于稻田（图2-h,图2-j）。

Table 2
表2
表2试验前后稻田和菜地土壤的基本理化性质
Table 2Soil organic carbon (SOC) and organic nitrogen (SON) contents, bulk density and pH of the 0-20 cm layer in double-rice and vegetable fields initially and 3 years later

	土壤有机碳 SOC (g?kg-1)	土壤有机氮 SON (g?kg-1)	容重 Bulk density (g?cm-3)	pH
Dec 2012
Rice	18.7 ± 1.0a	2.04 ± 0.28a	1.03 ± 0.09b	5.48 ± 0.29a
Veg	18.9 ± 1.2a	2.00 ± 0.36a	1.01 ± 0.07b	5.40 ± 0.18a
Dec 2015
Rice	19.1 ± 0.6a	2.12 ± 0.62a	1.01 ± 0.02b	5.39 ± 0.37a
Veg	17.2 ± 0.9b	1.74 ± 0.51b	1.39 ± 0.15a	4.34 ± 0.29b

Rice和Veg分别表示稻田和菜地;数据表示方式为平均值±标准误差;同一列中不同字母表示不同年份间稻田和菜地在P<0.05水平上存在显著性差异
Rice and Veg represent rice paddy and vegetable field, respectively; Values denote as means ± standard errors of three replicates; Different lowercase letters within the same column indicate significant difference between rice paddy and vegetable field at P<0.05 level

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图2

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图2观测期间稻田和菜地土壤性质变化

Rice和Veg分别表示稻田和菜地;数据表示方式为平均值±标准误差;*表示同一年份不同土地利用方式在P<0.05水平上存在显著性差异;不同字母表示同一土地利用方式不同年份间在P<0.05水平上存在显著性差异。图3、图4、图7同
Fig. 2Changes of soil properties in the double-rice and vegetable fields during the observation period

Rice and Veg represent rice paddy and vegetable field, respectively; Values denote as means ± standard errors of three replicates; * Indicates significant difference between rice paddy and vegetable field in the same year at P<0.05 level; Different letters indicate significant difference among years for the same land-use type at P<0.05 level. The same as Fig. 3, Fig. 4 and Fig. 7

2.2 CH₄和N₂O排放

稻田CH₄排放主要集中在水稻生长季,其累积排放量占全年CH₄排放总量的90%以上;稻田休闲季处于排水落干状态,其CH₄排放微弱（图3-a）。这些结果表明稻田CH₄具有明显的季节性排放特征。稻田第一年的CH₄排放强度（183.91 kg CH₄-C·hm^-2?a^-1）明显低于后续两年（241.56—371.50 kg CH₄-C·hm^-2?a^-1）,具有明显的年际变化差异（图3-c）。相对于稻田,新转菜地的CH₄排放量显著降低了83%—100%（图3-b、3-c）。稻田转菜地对CH₄排放的影响具有时间滞后效应：菜地第一年出现了明显的CH₄排放峰,使该年的CH₄累积排放量（31.22 kg CH₄-C·hm^-2）显著高于第二年（0.45 kg CH₄-C·hm^-2）和第三年（0.89 kg CH₄-C·hm^-2）。在整个观测期,土地利用方式转变及其与年份的交互作用均显著影响CH₄排放（图3-c）。

图3

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图3观测期间稻田和菜地CH₄排放通量及年累积排放量变化

Fig. 3Changes of fluxes and annual cumulative emissions of CH₄ from double-rice and vegetable fields during the observation period



在水稻生长季,稻田由于长期淹水,其N₂O排放通量在大部分观测期内维持在较低水平,甚至出现吸收大气N₂O的现象,但在排水晒田和复水等阶段出现了脉冲式N₂O排放峰的现象;稻田休闲季,N₂O排放通量低且相对较稳定（图4-a）。稻田是弱的N₂O排放源（1.35—3.49 kg N₂O-N·hm^-2?a^-1）,其转为菜地促进了N₂O排放（P<0.05,图4）。菜地N₂O排放主要集中在耕作、施肥并伴随灌溉后的15 d内。而且菜地N₂O排放通量在夏季较高,冬季较低,呈现明显的季节性变化规律。菜地N₂O排放具有明显的年际变化差异,其第一年的N₂O排放强度（95.12 kg N₂O·hm^-2?a^-1）显著高于第二年（38.28 kg N₂O-N·hm^-2?a^-1）和第三年（40.07 kg N₂O-N·hm^-2?a^-1）（图4-c）。在整个观测期内,年份、土地利用方式转变及其交互作用均显著影响N₂O排放（图4-c）。

图4

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图4观测期间稻田和菜地N₂O排放通量及年累积排放量变化

Fig. 4Changes of fluxes and annual cumulative emissions of N₂O from double-rice and vegetable fields during the observation period

2.3 影响CH₄和N₂O排放的主要因子

2.3.1 CH₄排放与环境因子间的关系 CH₄排放是CH₄产生和氧化过程综合作用的结果,其排放过程受诸多环境因子影响。本研究发现,土壤温度和水分均显著影响稻田CH₄排放（图5）。在3年观测期间,稻田CH₄排放通量随土壤温度的升高逐渐增强。当土壤温度<20℃时,CH₄排放通量对土壤温度的响应不明显;当土壤温度>20℃时,CH₄排放通量随土壤温度升高大幅度增加（图5-a）。土壤含水量与稻田CH₄排放通量间也呈现出显著的正相关关系（P<0.05,图5-b）。稻田转为菜地降低了土壤含水量,形成了好氧环境,减少了CH₄排放,使菜地CH₄排放通量与测定的其他环境因子之间的关系不显著。

图5

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图5稻田CH₄排放通量与土壤温度和水分含量间的关系

Fig. 5The relationship between CH₄ fluxes, and soil temperature and soil water content in double-rice field



2.3.2 N₂O排放与环境因子间的关系 在整个观测期间,稻田由于长期处于淹水状态,其N₂O排放低,与测定的环境因子之间不存在相关关系,说明土壤水分是限制稻田N₂O排放的主要因子。菜地N₂O排放通量与土壤异养呼吸（CO₂排放通量）呈正相关关系（P<0.05,图6）。特别是在转化的第一年（2013年）,菜地N₂O与CO₂排放通量的相关性达到了极显著水平（P<0.01）,决定系数R²为0.37。菜地土壤异养呼吸对其N₂O排放的影响在第一年高于第二和第三年,说明了稻田转菜地的第一年,有机质矿化对较高的N₂O排放有重要贡献。

图6

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图6菜地N₂O排放通量与土壤异养呼吸（CO₂排放通量）间的关系

Fig. 6Relationship between the fluxes of N₂O and soil heterotrophic respiration from vegetable field

2.4 综合增温潜势（GWP）估算

稻田和菜地的CH₄和N₂O排放特征在不同年份间存在差异。稻田CH₄年累积排放量显著高于菜地,而N₂O年累积排放量显著低于菜地。为进一步比较稻田和菜地的综合增温潜势（GWP）,本研究对CH₄和N₂O在100 年尺度上的GWP进行了计算（图7）。稻田转为蔬菜种植的第一和第二年,增加的N₂O增温潜势超过了减少的CH₄增温潜势,导致菜地的GWP相对于稻田分别显著增加了390%和98%。但是,稻田转为菜地的第三年,减少的CH₄ 增温潜势完全抵消了增加的N₂O增温潜势,使菜地的GWP（16.72±3.25 Mg CO₂-eq·hm^-2）与稻田（14.84±1.39 Mg CO₂-eq·hm^-2）相比无显著差异。这些研究结果表明稻田转菜地对GWP的影响主要集中在该土地利用方式转变的第一年。

图7

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图7稻田和菜地CH₄和N₂O年累积排放量及综合增温潜势（GWP）

Fig. 7Cumulative emissions of CH₄ and N₂O from rice and vegetable fields and the associated global warming potential

3 讨论

3.1 稻田转菜地对CH₄排放的影响

稻田是重要的CH₄排放源,其年累积排放量在第一年明显低于后续两年,这主要归功于后两年降雨量的增加引起了土壤水分含量的升高,从而促进了CH₄的产生和排放（图2-d,图3）。稻田转为菜地显著降低了CH₄排放（图3）。在3年观测期间,稻田转为菜地引起的CH₄排放减少量相当于稻田CH₄累积排放量的96%,这与YUAN等 ^[2]关于稻田转菜地降低CH₄排放的研究结果一致。CH₄的产生、氧化和传输等过程的综合作用导致了CH₄的净排放^[18,19]。稻田长期淹水形成的厌氧环境适合CH₄的产生。稻田转菜地显著降低了土壤温度和含水量（图2）,提高了土壤好氧状态,不仅导致CH₄产生过程受到抑制,同时也提高了甲烷氧化菌的活性 ^{[2-3, 20-22]}。然而,本研究发现稻田转为菜地第一年有CH₄排放峰（图3-b）。这主要是由于稻田转为菜地初始阶段,土壤结构中存在大量的微厌氧区,适宜CH₄的产生。排水落干也会使原来存储在土壤中的CH₄释放出来。这些因素的综合作用导致了菜地第一年出现了CH₄排放峰,使菜地在该年的CH₄累积排放量明显高于后续两年（图3-c）。该研究结果表明CH₄排放对稻田转菜地的响应存在时间滞后效应,在评价土地利用方式转变引起的环境效应时应充分考虑转变初始阶段CH₄的排放特征。

3.2 稻田转菜地对N₂O排放的影响

稻田是弱的N₂O排放源,甚至出现吸收大气N₂O的现象（图4-a）。这主要是由于稻田长期处于淹水状态,土壤氧化还原电位较低,从而使有机质矿化和硝化过程受到限制。而且稻田土壤中NO₃^--N含量低,限制了反硝化过程的进行^{[24, 26]}。稻田转为菜地促进了N₂O的大量排放^[5,24]。主要有以下几点原因：第一,稻田转为菜地改善了土壤的好氧状况,促进了硝化作用^[25,26];第二,菜地好气耕作会引起土壤团聚体结构的破坏,促进了原本被保护的土壤有机质的矿化,释放出大量的矿质态氮作为硝化和反硝化过程的底物^[14,27];第三,菜地相对较高的施氮量为硝化和反硝化过程提供了充足的底物^[28,29];第四,加速的土壤有机质矿化引起的氧气消耗容易形成厌氧微区,促进土壤硝化—反硝化耦合过程,从而增强了N₂O产生速率^{[15, 30-32]}。本研究观测期间,菜地的第一年N₂O累积排放量显著高于后续两年（图4-c）。前人也有研究表明,在我国南方丘陵地区双季稻田转为蔬菜种植的初始阶段也存在大量的N₂O排放^[2]。这些现象与本研究结果一致。稻田排水落干转为菜地加速了土壤有机质矿化,释放出了大量的可利用性碳、氮（表2;图2）,为土壤微生物硝化反硝化过程提供了能源物质和底物,从而引起N₂O的大量排放^[33,34]。菜地土壤异养呼吸与N₂O排放的显著正相关关系进一步说明了有机质矿化过程对N₂O排放有重要贡献（图6）。此外,稻田转菜地降低了土壤pH（表2）,在一定条件下可促进异养反硝化^[35]、氨氧化古菌主导的硝化^[36]、异养硝化^[37]、硝化-反硝化耦合^[31]、共反硝化（NO₃^--N + Organic N →N₂O）^[38]和化学反硝化^[39]等过程,同时也可能抑制N₂O还原过程,从而增强了N₂O排放^[40]。综上所述,稻田转为菜地增强了土壤好气性,降低了pH,加速了土壤有机质矿化,为土壤微生物硝化—反硝化耦合过程提供了大量的能源物质和底物,从而导致N₂O的大量排放,尤其是在稻田转为菜地的第一年。

3.3 稻田转菜地对综合增温潜势的影响

综合增温潜势（GWP）是评估陆地生态系统温室气体排放对气候变化潜在影响的重要指标^[41,42]。在100年尺度CO₂当量下,稻田转为菜地的第一和第二年,菜地的GWP显著高于稻田,这主要是由于菜地增加的N₂O增温潜势高于减少的CH₄增温潜势。然而,在稻田转为菜地的第三年,菜地的GWP与稻田相比无显著差异,这是由于菜地减少的CH₄增温潜势完全抵消了其增加的N₂O增温潜势（图7）。稻田转菜地第一年,土壤有机质矿化较快^[43],随后土壤有机质矿化速率逐渐降低,可利用性碳含量减少,限制了微生物氮转化过程,降低了N₂O排放^[27,34]。这些因素导致了菜地第三年的GWP显著低于第一和第二年,并与稻田GWP相比无明显差异。这表明GWP对稻田转菜地的响应主要集中在该土地利用方式转变的第一和第二年（图7）。因此,在评价农业土地利用方式转变引起的环境效应时,要重视转变初始阶段的温室气体排放特征,便于及时采取有效的温室气体减排措施,实现环境友好型农业可持续生产。

4 结论

稻田是重要的CH₄排放源,其转为菜地显著减少了CH₄排放。菜地第一年的CH₄排放量（31.22 kg CH₄-C·hm^-2）明显高于第二年（0.45 kg CH₄-C·hm^-2）和第三年（0.89 kg CH₄-C·hm^-2）。这些研究结果表明稻田转菜地对CH₄排放的影响具有时间滞后效应。稻田转为菜地增强了N₂O排放,且菜地第一年的N₂O排放量（95.12 kg N₂O-N·hm^-2）显著高于第二年（38.28 kg N₂O-N·hm^-2）和第三年（40.07 kg N₂O-N·hm^-2）。稻田转为菜地初期土壤有机质矿化对N₂O排放有重要贡献。在第一和第二年,菜地的GWP相对于稻田分别增加了390%和98%,主要是由于增加的N₂O增温潜势超过了减少的CH₄增温潜势。但是在第三年,菜地的GWP与稻田相比无显著差异,主要是由于减少的CH₄ 增温潜势完全抵消了增加的N₂O增温潜势。这些研究结果表明稻田转菜地对综合增温潜势的影响主要集中在该土地利用方式转变的第一年,表明了评价土地利用方式转变初始阶段温室气体排放特征的重要性,以便及时采取有效措施缓解农业土地利用方式转变引起的温室气体排放。

参考文献 View Option 原文顺序
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被引期刊影响因子

[1] Climate change 2013: The Physical Science Basis: Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change
Cambridge: Cambridge University Press, 2013.
[本文引用: 3]

[2] YUAN Y, DAI X, WANG H, XU M, FU X, YANG F. Effects of land-use conversion from double rice cropping to vegetables on methane and nitrous oxide fluxes in Southern China
PLoS One, 2015,26(1):147-154.
[本文引用: 4]

[3] LIU H, XING W, LI Z, WANG Q, DAN L, LIU G. Responses of soil methanogens, methanotrophs, and methane fluxes to land-use conversion and fertilization in a hilly red soil region of southern China
Environmental Science and Pollution Research, 2017,24(9):8731-8743.
DOI:10.1007/s11356-017-8628-yURLPMID:28213705 [本文引用: 2]
Changes in land-uses and fertilization are important factors regulating methane (CH4) emissions from paddy soils. However, the responses of soil CH4 emissions to these factors and the underlying mechanisms remain unclear. The objective of this study was to explore the effects of land-use conversion from paddies to orchards and fertilization on soil CH4 fluxes, and the abundance and community compositions of methanogens and methanotrophs. Soil CH4 fluxes were quantified by static chamber and gas chromatography technology. Abundance and community structures of methanogens and methanotrophs (based on mcrA and pmoA genes, respectively) were determined by quantitative real-time PCR (qPCR), and terminal restriction fragment length polymorphism (TRFLP), cloning and sequence analysis, respectively. Results showed that land-use conversion from paddies to orchards dramatically decreased soil CH4 fluxes, whereas fertilization did not distinctly affect soil CH4 fluxes. Furthermore, abundance of methanogens and methanotrophs were decreased after converting paddies to orchards. Fertilization decreased the abundance of these microorganisms, but the values were not statistically significant. Moreover, land-use conversion had fatal effects on some members of the methanogenic archaea (Methanoregula and Methanosaeta), increased type II methanotrophs (Methylocystis and Methylosinus), and decreased type I methanotrophs (Methylobacter and Methylococcus). However, fertilization could only significantly affect type I methanotrophs in the orchard plots. In addition, CH4 fluxes from paddy soils were positively correlated with soil dissolved organic carbon contents and methanogens abundance, whereas CH4 fluxes in orchard plots were negatively related to methanotroph abundance. Therefore, our results suggested that land-use conversion from paddies to orchards could change the abundance and community compositions of methanogens and methanotrophs, and ultimately alter the soil CH4 fluxes. Overall, our study shed insight on the underlying mechanisms of how land-use conversion from paddies to orchards decreased CH4 emissions.

[4] FAO. 2013. http://faostat.fao.org/beta/en/.
URL [本文引用: 1]

[5] ZHANG W, YU Y, LI T, SUN W, HUANG Y. Net greenhouse gas balance in China’s croplands over the last three decades and its mitigation potential
Environmental Science & Technology, 2014,48(5):2589-2597.
DOI:10.1021/es404352hURLPMID:24512240 [本文引用: 2]
Cropland soils have been shown to emit nitrous oxide (N2O) and methane (CH4) into the atmosphere and to sequester carbon when field management is improved, yet the spatiotemporal changes in the N2O and CH4 emissions and the soil organic carbon (SOC) in China's croplands are unclear with regard to an integrated global warming potential (GWP). This limits our overall evaluation of anthropogenic greenhouse gas (GHG) emissions and impairs effective decision making. On the basis of model simulations primarily from 1980 to 2009, we estimated a 69% increase in the gross GWP of CH4 and N2O emissions, from 244 Tg CO2-equiv yr(-1) in the early 1980s to 413 Tg CO2-equiv yr(-1) in the late 2000s. The SOC was estimated to have increased from 54 Tg CO2-equiv yr(-1) to 117 Tg CO2-equiv yr(-1) during the same period. A reduction in the carbon input during the rice season, along with an improvement of synthetic nitrogen use efficiency in crops to 40%, would mitigate GHG emissions by 111 Tg CO2-equiv yr(-1) and keep SOC sequestration at 82 Tg CO2 yr(-1). Together, this would amount to a reduction of 193 Tg CO2-equiv yr(-1), representing approximately 47% of the gross GWP in the late 2000s. The mitigation of GHG emissions in Henan, Shandong, Hunan, Jiangsu, Hubei, Sichuan, Anhui, Jiangxi, Guangdong and Hebei Provinces could lead to a approximately 66% national improvement and should be given priority.

[6] HAO H, SUN B, ZHAO Z. Effect of land use change from paddy to vegetable field on the residues of organochlorine pesticides in soils
Environmental Pollution, 2008,156(3):1046-1052.
DOI:10.1016/j.envpol.2008.04.021URLPMID:18554761 [本文引用: 1]
The effect of land use change from paddy to vegetable field on the residues of organochlorine pesticides (OCPs) was investigated. Soil residues of OCPs were analyzed in vegetable fields which had been converted from paddy fields for 0, 5, 10, 15, 20, 30, 50 year in Yixing, China in 2003. The mean concentrations of OCPs followed a sequence of: SigmaDDTs (13.7 microg kg(-1))> SigmaHCHs (8.6 microg kg(-1)) >>HCB (2.09 microg kg(-1))>alpha-endosulfan (1.30 microg kg(-1))>endrin (1.08 microg kg(-1))>PCNB (0.76 microg kg(-1))>dieldrin (0.58 microg kg(-1)). The mean residues of OCPs especially DDTs increased significantly with vegetable planting time after land use change in the first 15 years, then decreased from 20 to 30 years and increased a little afterward. The time under anaerobic and aerobic conditions was suggested to control mainly the change of the residues of OCPs.

[7] LU H, BAI Y, REN H, CAMPBELL DE. Integrated emergy, energy and economic evaluation of rice and vegetable production systems in alluvial paddy fields: implications for agricultural policy in China
Journal of Environmental Management, 2010,91(12):2727-2735.
DOI:10.1016/j.jenvman.2010.07.025URL [本文引用: 1]

Abstract

China is the largest rice producing and consuming country in the world, but rice production has given way to the production of vegetables during the past twenty years. The government has been trying to stop this land-use conversion and increase the area in rice-vegetable rotation. Important questions that must be answered to determine what strategy is best for society are, “What is the reason behind this conversion?”; “Which system is more productive and which is more sustainable?”; and “How can economic policy be used to adjust the pattern of farmland use to attain sustainable development?” To answer these questions, a combined evaluation of these agricultural production systems was done using emergy, energy and economic methods. An economic analysis clearly showed that the reason for this conversion was simply that the economic output/input ratio and the benefit density of the vegetable production system were greater than that of rice. However, both energy and emergy evaluations showed that long-term rice was the best choice for sustainable development, followed by rotation systems. The current price of rice is lower than the em-value of rice produced from the long-term rice system, but higher than that of rice produced from the rotation system. Scenario analysis showed that if the government increases the price of rice to the em-value of rice produced from the long-term rice system, US$0.4/kg, and takes the value of soil organic matter into account, the economic output/input ratios of both the rice and rotation systems will be higher than that of the vegetable system. The three methods, energy, emergy and economics, are different but complementary, each revealing a different aspect of the same system. Their combined use shows not only the reasons behind a system’s current state or condition, but also the way to adjust these systems to move toward more sustainable states.

[8] KRAUS D, WELLER S, JANZ B, KLATT S, SANTABáRBARA I, HAAS E, WERNER C, WASSMANN R, KIESE R, BUTTERBACH-BAHL K. How well can we assess impacts of agricultural land management changes on the total greenhouse gas balance (CO₂, CH₄ and N₂O) of tropical rice-cropping systems with biogeochemical models?
Agriculture, Ecosystems and Environment, 2016,224:104-115.
DOI:10.1016/j.agee.2016.03.037URL [本文引用: 1]

[9] WELLER S, JANZ B, J?RG L, KRAUS D, RACELA HSU, WASSMANN R, BUTTERBACH-BAHL K, KIESE R. Greenhouse gas emissions and global warming potential of traditional and diversified tropical rice rotation systems
Global Change Biology, 2016,22(1):432-448.
DOI:10.1111/gcb.13099URLPMID:26386203 [本文引用: 1]
Global rice agriculture will be increasingly challenged by water scarcity, while at the same time changes in demand (e.g. changes in diets or increasing demand for biofuels) will feed back on agricultural practices. These factors are changing traditional cropping patterns from double-rice cropping to the introduction of upland crops in the dry season. For a comprehensive assessment of greenhouse gas (GHG) balances, we measured methane (CH4 )/nitrous oxide (N2 O) emissions and agronomic parameters over 2.5 years in double-rice cropping (R-R) and paddy rice rotations diversified with either maize (R-M) or aerobic rice (R-A) in upland cultivation. Introduction of upland crops in the dry season reduced irrigation water use and CH4 emissions by 66-81% and 95-99%, respectively. Moreover, for practices including upland crops, CH4 emissions in the subsequent wet season with paddy rice were reduced by 54-60%. Although annual N2 O emissions increased two- to threefold in the diversified systems, the strong reduction in CH4 led to a significantly lower (P < 0.05) annual GWP (CH4 + N2 O) as compared to the traditional double-rice cropping system. Measurements of soil organic carbon (SOC) contents before and 3 years after the introduction of upland crop rotations indicated a SOC loss for the R-M system, while for the other systems SOC stocks were unaffected. This trend for R-M systems needs to be followed as it has significant consequences not only for the GWP balance but also with regard to soil fertility. Economic assessment showed a similar gross profit span for R-M and R-R, while gross profits for R-A were reduced as a consequence of lower productivity. Nevertheless, regarding a future increase in water scarcity, it can be expected that mixed lowland-upland systems will expand in SE Asia as water requirements were cut by more than half in both rotation systems with upland crops.

[10] NISHIMURA S, YONEMURA S, SAWAMOTO T, SHIRATO Y, AKIYAMA H, SUDO S, YAGI K. Effect of land use change from paddy rice cultivation to upland crop cultivation on soil carbon budget of a cropland in Japan
Agriculture, Ecosystems and Environment, 2008,125(1):9-20.
DOI:10.1016/j.agee.2007.11.003URL [本文引用: 2]

[11] JIANG C, WANG Y, ZHENG X, ZHU B, HUANG Y, HAO Q. Methane and nitrous oxide emissions from three paddy rice based cultivation systems in Southwest China
Advances in Atmospheric Sciences, 2006,23(3):415-424.
DOI:10.1007/s00376-006-0415-5URL [本文引用: 2]
To understand methane (CH₄) and nitrous oxide (N₂O) emissions from permanently flooded rice paddy fields and to develop mitigation options, a field experiment was conducted in situ for two years (from late 2002 to early 2005) in three rice-based cultivation systems, which are a permanently flooded rice field cultivated with a single time and followed by a non-rice season (PF), a rice-wheat rotation system (RW) and a rice-rapeseed rotation system (RR) in a hilly area in Southwest China. The results showed that the total CH₄ emissions from PF were 646.3±52.1 and 215.0±45.4 kg CH₄ hm⁻² during the rice-growing period and non-rice period, respectively. Both values were much lower than many previous reports from similar regions in Southwest China. The CH₄ emissions in the rice-growing season were more intensive in PF, as compared to RW and RR. Only 33% of the total annual CH₄ emission in PF occurred in the non-rice season, though the duration of this season is two times longer than the rice season. The annual mean N₂O flux in PF was 4.5±0.6 kg N₂O hm⁻² yr⁻¹. The N₂O emission in the rice-growing season was also more intensive than in the non-rice season, with only 16% of the total annual emission occurring in the non-rice season. The amounts of N₂O emission in PF were ignorable compared to the CH₄ emission in terms of the global warming potential (GWP). Changing PF to RW or RR not only eliminated CH₄ emissions in the non-rice season, but also substantially reduced the CH₄ emission during the following rice-growing period (ca. 58%, P<0.05). However, this change in cultivation system substantially increased N₂O emissions, especially in the non-rice season, by a factor of 3.7 to 4.5. On the 100-year horizon, the integrated GWP of total annual CH₄ and N₂O emissions satisfies PF≫RR≈RW. The GWP of PF is higher than that of RW and RR by a factor of 2.6 and 2.7, respectively. Of the total GWP of CH₄ and N₂O emissions, CH₄ emission contributed to 93%, 65% and 59% in PF, RW and RR, respectively. These results suggest that changing PF to RW and RR can substantially reduce not only CH₄ emission but also the total GWP of the CH₄ and N₂O emissions.

[12] KONG A Y, FONTE S J, VAN KESSEL C, SIX J. Transitioning from standard to minimum tillage: Trade-offs between soil organic matter stabilization, nitrous oxide emissions, and N availability in irrigated cropping systems
Soil & Tillage Research, 2009,104(2):256-262.
[本文引用: 1]

[13] SHENG R, MENG D, WU M, DI H, QIN H, WEI W. Effect of agricultural land use change on community composition of bacteria and ammonia oxidizers
Journal of Soils and Sediments, 2013,13(7):1246-1256.
DOI:10.1007/s11368-013-0713-3URL [本文引用: 1]

Purpose

Soil microbial communities can be strongly influenced by agricultural practices, but little is known about bacterial community successions as land use changes. The objective of this study was to determine microbial community shifts following major land use changes in order to improve our understanding of land use impacts on microbial community composition and functions.

Materials and methods

Four agricultural land use patterns were selected for the study, including old rice paddy fields (ORP), Magnolia nursery planting (MNP), short-term vegetable (STV), and long-term vegetable (LTV) cultivation. All four systems are located in the same region with same soil parent material (alluvium), and the MNP, STV, and LTV systems had been converted from ORP for 10, 3, and 30?years, respectively. Soil bacteria and ammonia oxidizer community compositions were analyzed by 454 pyrosequencing and terminal restriction fragment length polymorphism, respectively. Quantitative PCR was used to determine 16S rRNA and amoA gene copy numbers.

Results and discussion

The results showed that when land use was changed from rice paddy to upland systems, the relative abundance of Chloroflexi increased whereas Acidobacteria decreased significantly. While LTV induced significant shifts of bacterial composition, MNP had the highest relative abundance of genera GP1, GP2, and GP3, which were mainly related to the development of soil acidity. The community composition of ammonia-oxidizing bacteria (AOB) but not ammonia-oxidizing archaea was strongly impacted by the agricultural land use patterns, with LTV inducing the growth of a single super predominant AOB group. The land use changes also induced significant shifts in the abundance of 16S rRNA and bacterial amoA genes, but no significant differences in the abundance of archaea amoA was detected among the four land use patterns. Soil total phosphorous, available phosphorous, NO₃^?, and soil organic carbon contents and pH were the main determinants in driving the composition of both bacteria and AOB communities.

Conclusions

These results clearly show the significant impact of land use change on soil microbial community composition and abundance and this will have major implications on the microbial ecology and nutrient cycling in these systems, some of which is unknown. Further research should be directed to studying the impacts of these microbial community shifts on nutrient dynamics in these agroecosystems so that improved nutrient management systems can be developed.



[14] WANG H, GUAN D, ZHANG R, CHEN Y, HU Y, XIAO L. Soil aggregates and organic carbon affected by the land use change from rice paddy to vegetable field
Ecological Engineering, 2014,70:206-211.
DOI:10.1016/j.ecoleng.2014.05.027URL [本文引用: 2]

[15] WANG W, DALAL R C, REEVES S H, BUTTERBACH-BAHL K, KIESE R. Greenhouse gas fluxes from an Australian subtropical cropland under long-term contrasting management regimes
Global Change Biology, 2011,17(10):3089-3101.
DOI:10.1111/j.1365-2486.2011.02458.xURL [本文引用: 2]
The long-term effects of conservation management practices on greenhouse gas fluxes from tropical/subtropical croplands remain to be uncertain. Using both manual and automatic sampling chambers, we measured N(2)O and CH(4) fluxes at a long-term experimental site (1968-present) in Queensland, Australia from 2006 to 2009. Annual net greenhouse gas fluxes (NGGF) were calculated from the 3-year mean N(2)O and CH(4) fluxes and the long-term soil organic carbon changes. N(2)O emissions exhibited clear daily, seasonal and interannual variations, highlighting the importance of whole-year measurement over multiple years for obtaining temporally representative annual emissions. Averaged over 3 years, annual N(2)O emissions from the unfertilized and fertilized soils (90 kg N ha(-1) yr(-1) as urea) amounted to 138 and 902 g N ha(-1), respectively. The average annual N(2)O emissions from the fertilized soil were 388 g N ha(-1) lower under no-till (NT) than under conventional tillage (CT) and 259 g N ha(-1) higher under stubble retention (SR) than under stubble burning (SB). Annual N(2)O emissions from the unfertilized soil were similar between the contrasting tillage and stubble management practices. The average emission factors of fertilizer N were 0.91%, 1.20%, 0.52% and 0.77% for the CT-SB, CT-SR, NT-SB and NT-SR treatments, respectively. Annual CH(4) fluxes from the soil were very small (-200-300 g CH(4) ha(-1) yr(-1)) with no significant difference between treatments. The NGGF were 277-350 kg CO(2)-e ha(-1) yr(-1) for the unfertilized treatments and 401-710 kg CO(2)-e ha(-1) yr(-1) for the fertilized treatments. Among the fertilized treatments, N(2)O emissions accounted for 52-97% of NGGF and NT-SR resulted in the lowest NGGF (401 kg CO(2)-e ha(-1) yr(-1) or 140 kg CO(2)-e t(-1) grain). Therefore, NT-SR with improved N fertilizer management practices was considered the most promising management regime for simultaneously achieving maximal yield and minimal NGGF.

[16] 龚子同, 张甘霖, 陈志诚. 土壤发生与系统分类. 北京: 科学出版社, 2007.
[本文引用: 1]

GONG Z T, ZHANG G L, CHEN Z C. Pedogenesis and Soil Taxonomy. Beijing: Science Press, 2007. (in Chinese)
[本文引用: 1]

[17] 鲍士旦. 土壤农化分析. 北京: 中国农业出版社, 2005.
[本文引用: 2]

BAO S D. Soil and Agricultural Chemistry Analysis. Beijing: China Agricultural Press, 2005. (in Chinese)
[本文引用: 2]

[18] 朱晓晴, 安晶, 马玲, 陈松岭, 李嘉琦, 邹洪涛, 张玉龙. 秸秆还田深度对土壤温室气体排放及玉米产量的影响
中国农业科学, 2020,53(5):977-989.
DOI:10.3864/j.issn.0578-1752.2020.05.010URL [本文引用: 1]
【Objective】 Straw returning is an important technical means to improve soil fertility, increase soil organic matter and improve soil structure. However, previous studies have shown that straw returning can accelerate the emission of greenhouse gases in soil and increase greenhouse effect. Through the study of greenhouse gas emission characteristics and maize yield of farmland soil under different straw returning depths, the optimum returning depths were determined in this study, in order to provide scientific basis for rational utilization of straw, increase crop yield and realize sustainable agricultural development. 【Method】 In the field micro-plot experiment, maize was used as the test crop, and four returning depths were set up, which were 0-10 cm (T1), 10-20 cm (T2), 20-30 cm (T3) and 30-40 cm (T4), respectively. At the same time, the non-returning treatment was used as the control (CK), with a total of five treatments. Static box-gas chromatography was used to determine the greenhouse gases (CO₂, CH₄, N₂O) emission characteristics under different returning depths in whole maize growing season, and yield and yield components at maturity were measured. 【Result】 (1) During the whole maize growing season, both CO₂ and N₂O showed emission, but CH₄ showed absorption. The cumulative emission of CO₂ was the highest under T3 treatment, which increased by 28.6% significantly compared with CK. The increase rate of cumulative emission of CO₂ under T4 treatment was the least, which was significantly increased by 17.1% compared with CK (P<0.05), but the difference between T1 and T4 treatment was not significant; the cumulative emission of N₂O was the highest under T2 treatment. Compared with CK, the cumulative amount of N₂O increased significantly by 111.3%, the increase rate under T4 treatment was the least, and the CK increased significantly by 12.8% (P<0.05). However, CH₄ showed absorption, and the absorption capacity of CH₄ in farmland soil was reduced after straw returning; the absorption capacity was CK treatment>T4 treatment>T1 treatment>T3 treatment>T2 treatment, and there were significant differences between treatments and CK (P<0.05). (2) Compared with the control, the yield of maize in each treatment increased significantly, and the yield increased by 5.6%-20.8% (P<0.05). However, there were no significant difference in ear length, ear diameter and grain number between treatments. When the straw returned to 30-40 cm, the yield was the highest, which increased by 20.76% than that under CK, and it indicated that straw returning had an important effect on improving soil fertility and increasing crop yield. (3) According to the comprehensive greenhouse gas effect (GWP) and greenhouse gas emission intensity (GHGI), on the scale of 100 years, GWP showed T2 treatment>T3 treatment>T1 treatment>T4 treatment>CK treatment, while GHGI showed T2 treatment>T3 treatment>T1 treatment>CK treatment>T4 treatment. Compared with CK, all treatments increased the comprehensive greenhouse gas effect, while T4 treatment reduced greenhouse gas emission intensity in maize season, indicating that straw returning to 30-40 cm could alleviate the global warming trend to a certain extent. 【Conclusion】 Straw returning could increase CO₂ and N₂O emissions significantly, but increase the absorption capacity of CH₄. The straw returning to 30-40 cm could reduce the global warming potential and the intensity of greenhouse gas emissions, and increase the maize yield significantly. Therefore, in order to simultaneously achieve higher maize yield and lower greenhouse gas emission intensity, straw returning to 30-40 cm was a more reasonable way of soil improvement and fertilization.
ZHU X Q, AN J, MA L, CHEN S L, LI J Q, ZOU H T, ZHANG Y L. Effects of different straw returning depths on soil greenhouse gas emission and maize yield
Scientia Agricultura Sinica, 2020,53(5):977-989. (in Chinese)
DOI:10.3864/j.issn.0578-1752.2020.05.010URL [本文引用: 1]
【Objective】 Straw returning is an important technical means to improve soil fertility, increase soil organic matter and improve soil structure. However, previous studies have shown that straw returning can accelerate the emission of greenhouse gases in soil and increase greenhouse effect. Through the study of greenhouse gas emission characteristics and maize yield of farmland soil under different straw returning depths, the optimum returning depths were determined in this study, in order to provide scientific basis for rational utilization of straw, increase crop yield and realize sustainable agricultural development. 【Method】 In the field micro-plot experiment, maize was used as the test crop, and four returning depths were set up, which were 0-10 cm (T1), 10-20 cm (T2), 20-30 cm (T3) and 30-40 cm (T4), respectively. At the same time, the non-returning treatment was used as the control (CK), with a total of five treatments. Static box-gas chromatography was used to determine the greenhouse gases (CO₂, CH₄, N₂O) emission characteristics under different returning depths in whole maize growing season, and yield and yield components at maturity were measured. 【Result】 (1) During the whole maize growing season, both CO₂ and N₂O showed emission, but CH₄ showed absorption. The cumulative emission of CO₂ was the highest under T3 treatment, which increased by 28.6% significantly compared with CK. The increase rate of cumulative emission of CO₂ under T4 treatment was the least, which was significantly increased by 17.1% compared with CK (P<0.05), but the difference between T1 and T4 treatment was not significant; the cumulative emission of N₂O was the highest under T2 treatment. Compared with CK, the cumulative amount of N₂O increased significantly by 111.3%, the increase rate under T4 treatment was the least, and the CK increased significantly by 12.8% (P<0.05). However, CH₄ showed absorption, and the absorption capacity of CH₄ in farmland soil was reduced after straw returning; the absorption capacity was CK treatment>T4 treatment>T1 treatment>T3 treatment>T2 treatment, and there were significant differences between treatments and CK (P<0.05). (2) Compared with the control, the yield of maize in each treatment increased significantly, and the yield increased by 5.6%-20.8% (P<0.05). However, there were no significant difference in ear length, ear diameter and grain number between treatments. When the straw returned to 30-40 cm, the yield was the highest, which increased by 20.76% than that under CK, and it indicated that straw returning had an important effect on improving soil fertility and increasing crop yield. (3) According to the comprehensive greenhouse gas effect (GWP) and greenhouse gas emission intensity (GHGI), on the scale of 100 years, GWP showed T2 treatment>T3 treatment>T1 treatment>T4 treatment>CK treatment, while GHGI showed T2 treatment>T3 treatment>T1 treatment>CK treatment>T4 treatment. Compared with CK, all treatments increased the comprehensive greenhouse gas effect, while T4 treatment reduced greenhouse gas emission intensity in maize season, indicating that straw returning to 30-40 cm could alleviate the global warming trend to a certain extent. 【Conclusion】 Straw returning could increase CO₂ and N₂O emissions significantly, but increase the absorption capacity of CH₄. The straw returning to 30-40 cm could reduce the global warming potential and the intensity of greenhouse gas emissions, and increase the maize yield significantly. Therefore, in order to simultaneously achieve higher maize yield and lower greenhouse gas emission intensity, straw returning to 30-40 cm was a more reasonable way of soil improvement and fertilization.

[19] INUBUSHI K, CHENG W, AONUMA S, HOQUE MM, KOBAYASHI K, MIURA S, KIM HY, OKADA M. Effects of free-air CO₂ enrichment (FACE) on CH₄ emission from a rice paddy field
Global Change Biology, 2003,9(10):1458-1464.
DOI:10.1046/j.1365-2486.2003.00665.xURL [本文引用: 1]

[20] BREIDENBACH B, BLASER MB, KLOSE M, CONRAD R. Crop rotation of flooded rice with upland maize impacts the resident and active methanogenic microbial community
Environmental Microbiology, 2015,18(9):2868-2885.
DOI:10.1111/1462-2920.13041URLPMID:26337675 [本文引用: 1]
Crop rotation of flooded rice with upland crops is a common management scheme allowing the reduction of water consumption along with the reduction of methane emission. The introduction of an upland crop into the paddy rice ecosystem leads to dramatic changes in field conditions (oxygen availability, redox conditions). However, the impact of this practice on the archaeal and bacterial communities has scarcely been studied. Here, we provide a comprehensive study focusing on the crop rotation between flooded rice in the wet season and upland maize (RM) in the dry season in comparison with flooded rice (RR) in both seasons. The composition of the resident and active microbial communities was assessed by 454 pyrosequencing targeting the archaeal and bacterial 16S rRNA gene and 16S rRNA. The archaeal community composition changed dramatically in the rotational fields indicated by a decrease of anaerobic methanogenic lineages and an increase of aerobic Thaumarchaeota. Members of Methanomicrobiales, Methanosarcinaceae, Methanosaetaceae and Methanocellaceae were equally suppressed in the rotational fields indicating influence on both acetoclastic and hydrogenotrophic methanogens. On the contrary, members of soil crenarchaeotic group, mainly Candidatus Nitrososphaera, were higher in the rotational fields, possibly indicating increasing importance of ammonia oxidation during drainage. In contrast, minor effects on the bacterial community were observed. Acidobacteria and Anaeromyxobacter spp. were enriched in the rotational fields, whereas members of anaerobic Chloroflexi and sulfate-reducing members of Deltaproteobacteria were found in higher abundance in the rice fields. Combining quantitative polymerase chain reaction and pyrosequencing data revealed increased ribosomal numbers per cell for methanogenic species during crop rotation. This stress response, however, did not allow the methanogenic community to recover in the rotational fields during re-flooding and rice cultivation. In summary, the analyses showed that crop rotation with upland maize led to dramatic changes in the archaeal community composition whereas the bacterial community was only little affected.

[21] LIU D, ISHIKAWA H, NISHIDA M, TSUCHIYA K, TAKAHASHI T, KIMURA M, ASAKAWA S. Effect of paddy-upland rotation on methanogenic archaeal community structure in paddy field soil
Microbial Ecology, 2015,69(1):160-168.
DOI:10.1007/s00248-014-0477-3URLPMID:25113614
Methanogenic archaea are strict anaerobes and demand highly reduced conditions to produce methane in paddy field soil. However, methanogenic archaea survive well under upland and aerated conditions in paddy fields and exhibit stable community. In the present study, methanogenic archaeal community was investigated in fields where paddy rice (Oryza sativa L.) under flooded conditions was rotated with soybean (Glycine max [L.] Merr.) under upland conditions at different rotation histories, by polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) and real-time quantitative PCR methods targeting 16S rRNA and mcrA genes, respectively. Soil samples collected from the fields before flooding or seeding, during crop cultivation and after harvest of crops were analyzed. The abundance of the methanogenic archaeal populations decreased to about one-tenth in the rotational plots than in the consecutive paddy (control) plots. The composition of the methanogenic archaeal community also changed. Most members of the methanogenic archaea consisting of the orders Methanosarcinales, Methanocellales, Methanomicrobiales, and Methanobacteriales existed autochthonously in both the control and rotational plots, while some were strongly affected in the rotational plots, with fatal effect to some members belonging to the Methanosarcinales. This study revealed that the upland conversion for one or longer than 1 year in the rotational system affected the methanogenic archaeal community structure and was fatal to some members of methanogenic archaea in paddy field soil.

[22] AULAKH M S, WASSMANN R, RENNENBERG H. Methane emissions from rice fields-quantification, mechanisms, role of management, and mitigation options
Advances in Agronomy, 2001,70:193-260.
[本文引用: 1]

[24] WU L, TANG S, HE D, WU X, SHAABAN M, WANG M, ZHAO J, KHAN I, ZHENG X, HU R. Conversion from rice to vegetable production increases N₂O emission via increased soil organic matter mineralization
Science of the Total Environment, 2017,583:190-201.
DOI:10.1016/j.scitotenv.2017.01.050URL [本文引用: 2]

[25] REPO M E, SUSILUOTO S, LIND S E, JOKINEN S, ELSAKOV V, BIASI C, VIRTANEN T, MARTIKAINEN P J. Large N₂O emissions from cryoturbated peat soil in tundra
Nature Geoscience, 2009,2(3):189-192.
DOI:10.1038/ngeo434URL [本文引用: 1]

[26] SHANG Q, YANG X, GAO C, WU P, LIU J, XU Y, SHEN Q, ZOU J, GUO S. Net annual global warming potential and greenhouse gas intensity in Chinese double rice-cropping systems: A 3-year field measurement in long-term fertilizer experiments
Global Change Biology, 2011,17(6):2196-2210.
DOI:10.1111/j.1365-2486.2010.02374.xURL [本文引用: 2]
The impact of agricultural management on global warming potential (GWP) and greenhouse gas intensity (GHGI) is not well documented. A long-term fertilizer experiment in Chinese double rice-cropping systems initiated in 1990 was used in this study to gain an insight into a complete greenhouse gas accounting of GWP and GHGI. The six fertilizer treatments included inorganic fertilizer [nitrogen and phosphorus fertilizer (NP), nitrogen and potassium fertilizer (NK), and balanced inorganic fertilizer (NPK)], combined inorganic/organic fertilizers at full and reduced rate (FOM and ROM), and no fertilizer application as a control. Methane (CH4) and nitrous oxide (N2O) fluxes were measured using static chamber method from November 2006 through October 2009, and the net ecosystem carbon balance was estimated by the changes in topsoil (0-20 cm) organic carbon (SOC) density over the 10-year period 1999-2009. Long-term fertilizer application significantly increased grain yields, except for no difference between the NK and control plots. Annual topsoil SOC sequestration rate was estimated to be 0.96 t C ha-1 yr-1 for the control and 1.01-1.43 t C ha-1 yr-1 for the fertilizer plots. Long-term inorganic fertilizer application tended to increase CH4 emissions during the flooded rice season and significantly increased N2O emissions from drained soils during the nonrice season. Annual mean CH4 emissions ranged from 621 kg CH4 ha-1 for the control to 1175 kg CH4 ha-1 for the FOM plots, 63-83% of which derived from the late-rice season. Annual N2O emission averaged 1.15-4.11 kg N2O-N ha-1 in the double rice-cropping systems. Compared with the control, inorganic fertilizer application slightly increased the net annual GWPs, while they were remarkably increased by combined inorganic/organic fertilizer application. The GHGI was lowest for the NP and NPK plots and highest for the FOM and ROM plots. The results of this study suggest that agricultural economic viability and GHGs mitigation can be simultaneously achieved by balanced fertilizer application.

[27] GRANDY A, ROBERTSON G. Initial cultivation of a temperate- region soil immediately accelerates aggregate turnover and CO₂ and N₂O fluxes
Global Change Biology, 2006,12(8):1507-1520.
DOI:10.1111/gcb.2006.12.issue-8URL [本文引用: 2]

[28] ZhANG Y, LIN F, JIN Y, WANG X, LIU S, ZOU J. Response of nitric and nitrous oxide fluxes to N fertilizer application in greenhouse vegetable cropping systems in southeast China
Scientific Reports, 2016,6:20700.
DOI:10.1038/srep20700URLPMID:26848094 [本文引用: 1]
It is of great concern worldwide that active nitrogenous gases in the global nitrogen cycle contribute to regional and global-scale environmental issues. Nitrous oxide (N2O) and nitric oxide (NO) are generally interrelated in soil nitrogen biogeochemical cycles, while few studies have simultaneously examined these two gases emission from typical croplands. Field experiments were conducted to measure N2O and NO fluxes in response to chemical N fertilizer application in annual greenhouse vegetable cropping systems in southeast China. Annual N2O and NO fluxes averaged 52.05 and 14.87 mug N m(-2) h(-1) for the controls without N fertilizer inputs, respectively. Both N2O and NO emissions linearly increased with N fertilizer application. The emission factors of N fertilizer for N2O and NO were estimated to be 1.43% and 1.15%, with an annual background emission of 5.07 kg N2O-N ha(-1) and 1.58 kg NO-N ha(-1), respectively. The NO-N/N2O-N ratio was significantly affected by cropping type and fertilizer application, and NO would exceed N2O emissions when soil moisture is below 54% WFPS. Overall, local conventional input rate of chemical N fertilizer could be partially reduced to attain high yield of vegetable and low N2O and NO emissions in greenhouse vegetable cropping systems in China.

[29] 奚雅静, 汪俊玉, 李银坤, 武雪萍, 李晓秀, 王碧胜, 李生平, 宋霄君, 刘彩彩. 滴灌水肥一体化配施有机肥对土壤N₂O排放与酶活性的影响
中国农业科学, 2019,52(20):3611-3624.
DOI:10.3864/j.issn.0578-1752.2019.20.012URL [本文引用: 1]
【Objective】 This paper mainly studied the dynamic changes of soil N₂O emission and the activities of urease (UR), nitrate reductase (NR), nitrite reductase (Ni R) and hydroxylamine reductase (Hy R) under the condition of drip irrigation water and fertilizer integration by applying different amounts of inorganic nitrogen to organic nitrogen, and analyzed the soil N₂O emission characteristics of every treatment and the effects of soil UR, NR, Ni R and Hy R activities on soil N₂O emissions, the purpose of this research was to reveal the influence mechanism of N₂O emission process under the integration of drip irrigation water and fertilizer.【Method】 The treatments consisted of CK (no nitrogen application), N1 (200 kg·hm ^-2 organic nitrogen), N2 (200 kg·hm ^-2organic nitrogen + 250 kg·hm ^-2 inorganic nitrogen), and N3 (200 kg·hm ^-2 organic nitrogen + 475 kg·hm ^-2inorganic nitrogen). Using static-chamber method, the soil N₂O emission, enzyme activity, soil temperature and humidity during the growth period of tomato were monitored.【Result】 The integration of water and fertilizer in drip irrigation showed that the N₂O emission peak of every treatment appeared at the first day after fertilization + irrigation, and decreased continuously with the passage of time. The N₂O emission flux range under different treatments was 0.98-1544.79 μg·m ^-2·h ^-1. The total N₂O emissions during the growth period of tomato under different treatments had significant differences among each treatment, which were N3 ((7.13±0.11) kg·hm ^-2) >N2 ((4.87±0.21) kg·hm ^-2) >N1 ((2.54±0.17) kg·hm ^-2) >CK ((1.56±0.23) kg·hm ^-2). Compared with N3, the total soil N₂O emissions from N1 and N2 decreased by 64.38% and 31.70%, respectively. During the growth period of tomato, the characteristics of seasonal emission of N₂O changed obviously, which revealed high in autumn and low in winter. The activity of soil nitrogen-related enzymes increased with the increase of nitrogen application rate. The soil N₂O flux was positively correlated with 5 cm soil temperature, 0-10 cm soil nitrate nitrogen content, soil NR activity and soil Hy R activity (P<0.01).【Conclusion】 Under the integration of drip irrigation and water and fertilizer, soil N₂O mainly came from the nitrification process, which reduced the N₂O emissions generated by the denitrification process. Considering the factors such as tomato yield, quality and N₂O emission, it was recommended to apply 200 kg·hm ^-2organic nitrogen +250 kg·hm ^-2 inorganic nitrogen, 75 kg·hm ^-2 P₂O₅ and 450 kg·hm ^-2 K₂O in northern greenhouse autumn-winter tomato.
XI Y J, WANG J Y, LI Y K, WU X P, LI X X, WANG B S, LI S P, SONG X J, LIU C C. Effects of drip irrigation water and fertilizer integration combined with organic fertilizers on soil N₂O emission and enzyme activity
Scientia Agricultura Sinica, 2019,52(20):3611-3624. (in Chinese)
DOI:10.3864/j.issn.0578-1752.2019.20.012URL [本文引用: 1]
【Objective】 This paper mainly studied the dynamic changes of soil N₂O emission and the activities of urease (UR), nitrate reductase (NR), nitrite reductase (Ni R) and hydroxylamine reductase (Hy R) under the condition of drip irrigation water and fertilizer integration by applying different amounts of inorganic nitrogen to organic nitrogen, and analyzed the soil N₂O emission characteristics of every treatment and the effects of soil UR, NR, Ni R and Hy R activities on soil N₂O emissions, the purpose of this research was to reveal the influence mechanism of N₂O emission process under the integration of drip irrigation water and fertilizer.【Method】 The treatments consisted of CK (no nitrogen application), N1 (200 kg·hm ^-2 organic nitrogen), N2 (200 kg·hm ^-2organic nitrogen + 250 kg·hm ^-2 inorganic nitrogen), and N3 (200 kg·hm ^-2 organic nitrogen + 475 kg·hm ^-2inorganic nitrogen). Using static-chamber method, the soil N₂O emission, enzyme activity, soil temperature and humidity during the growth period of tomato were monitored.【Result】 The integration of water and fertilizer in drip irrigation showed that the N₂O emission peak of every treatment appeared at the first day after fertilization + irrigation, and decreased continuously with the passage of time. The N₂O emission flux range under different treatments was 0.98-1544.79 μg·m ^-2·h ^-1. The total N₂O emissions during the growth period of tomato under different treatments had significant differences among each treatment, which were N3 ((7.13±0.11) kg·hm ^-2) >N2 ((4.87±0.21) kg·hm ^-2) >N1 ((2.54±0.17) kg·hm ^-2) >CK ((1.56±0.23) kg·hm ^-2). Compared with N3, the total soil N₂O emissions from N1 and N2 decreased by 64.38% and 31.70%, respectively. During the growth period of tomato, the characteristics of seasonal emission of N₂O changed obviously, which revealed high in autumn and low in winter. The activity of soil nitrogen-related enzymes increased with the increase of nitrogen application rate. The soil N₂O flux was positively correlated with 5 cm soil temperature, 0-10 cm soil nitrate nitrogen content, soil NR activity and soil Hy R activity (P<0.01).【Conclusion】 Under the integration of drip irrigation and water and fertilizer, soil N₂O mainly came from the nitrification process, which reduced the N₂O emissions generated by the denitrification process. Considering the factors such as tomato yield, quality and N₂O emission, it was recommended to apply 200 kg·hm ^-2organic nitrogen +250 kg·hm ^-2 inorganic nitrogen, 75 kg·hm ^-2 P₂O₅ and 450 kg·hm ^-2 K₂O in northern greenhouse autumn-winter tomato.

[30] GARCIA-MONTIEL D, MELILLO J, STEUDLER P, CERRI C, PICCOLO M. Carbon limitations to nitrous oxide emissions in a humid tropical forest of the Brazilian Amazon
Biology and Fertility of Soils, 2003,38(5):267-272.
DOI:10.1007/s00374-003-0637-yURL [本文引用: 1]
The availability of labile organic C for microbial metabolic processes could be an important factor regulating N₂O emissions from tropical soils. We explored the effects of labile C on the emissions of N₂O from a forest soil in the State of Rondônia in the southwestern quadrant of the Brazilian Amazon. We measured emissions of N₂O from a forest soil after amendments with solutions containing glucose, water only or NO₃^–. Addition of glucose to the forest soil resulted in very large increases in N₂O emissions whereas the water only and NO₃^– additions did not. These results suggest a strong C limitation on N₂O production in this forest soil in the southwestern Amazon.

[31] PENTON C R, DEENIK J L, POPP B N, BRULAND G L, ENGSTROM P, LOUIS D S, TIEDJE J. Importance of sub-surface rhizosphere-mediated coupled nitrification-denitrification in a flooded agroecosystem in Hawaii
Soil Biology and Biochemistry, 2013,57:362-373.
DOI:10.1016/j.soilbio.2012.10.018URL [本文引用: 1]
The fate of fertilizer nitrogen (N) in flooded agroecosystems is difficult to predict given the multitude of potential N transformation pathways. In particular, rhizosphere effects are known to play a significant role in N cycling, but are especially difficult to quantify in large emergent macrophytes. To address these issues, we utilized a whole core (NH4+)-N-15 perfusion technique with porewater equilibrators for the extraction of N14+15-NO3-, NH4+, and N-2. Sub-surface denitrification was found to be an important N loss pathway in wetland sediments vegetated with aerenchymatous taro (Colocasia esculenta) versus bare sediments. Driven by hypothesized thermo-osmotic mechanisms linked to photosynthesis, diurnal O-2 transport into the sub-surface stimulated nitrification-denitrification in the extensive root rhizosphere. Porewater denitrification rates were also positively influenced by airflow across leaf surfaces. Depth-integrated porewater denitrification rates in this system were very high, ranging from 23 to 845 mu mol N-2 m(-2) h(-1). The N cycling functional genes nosZ and amoA were found at high abundances throughout the sub-surface with nirS dominating nitrite reduction in these sediments. Overall we were able to account for >82% of added (NH4+)-N-15 in the vegetated cores over a ten-day incubation through both plant incorporation and surface/sub-surface coupled nitrification-denitrification. In summary, these results suggested (1) that oxygen flux through the taro stem and root system into the flooded sediment may be an important driver of nitrification and coupled denitrification in these systems, and (2) that oxygen flux is mediated by air movement (wind) and the diurnal light-cycle related to photosynthesis. Published by Elsevier Ltd.

[32] DEPPE M, WELL R, GIESEMANN A, SPOTT O, FLESSA H. Soil N₂O fluxes and related processes in laboratory incubations simulating ammonium fertilizer depots
Soil Biology and Biochemistry, 2017,104:68-80.
DOI:10.1016/j.soilbio.2016.10.005URL [本文引用: 1]

[33] NIKIèMA P, ROTHSTEIN D E, MILLER R O. Initial greenhouse gas emissions and nitrogen leaching losses associated with converting pastureland to short-rotation woody bioenergy crops in northern Michigan, USA
Biomass Bioenergy, 2012,39:413-426.
DOI:10.1016/j.biombioe.2012.01.037URL [本文引用: 1]

[34] GRANDY A, ROBERTSON G. Aggregation and organic matter protection following tillage of a previously uncultivated soil
Soil Science Society of America Journal, 2006,70(4):1398-1406.
DOI:10.2136/sssaj2005.0313URL [本文引用: 2]

[35] ZUMFT W G. Cell biology and molecular basis of denitrification
Microbiology and Molecular Biology Reviews, 1997,61(4):533-616.
URLPMID:9409151 [本文引用: 1]
Denitrification is a distinct means of energy conservation, making use of N oxides as terminal electron acceptors for cellular bioenergetics under anaerobic, microaerophilic, and occasionally aerobic conditions. The process is an essential branch of the global N cycle, reversing dinitrogen fixation, and is associated with chemolithotrophic, phototrophic, diazotrophic, or organotrophic metabolism but generally not with obligately anaerobic life. Discovered more than a century ago and believed to be exclusively a bacterial trait, denitrification has now been found in halophilic and hyperthermophilic archaea and in the mitochondria of fungi, raising evolutionarily intriguing vistas. Important advances in the biochemical characterization of denitrification and the underlying genetics have been achieved with Pseudomonas stutzeri, Pseudomonas aeruginosa, Paracoccus denitrificans, Ralstonia eutropha, and Rhodobacter sphaeroides. Pseudomonads represent one of the largest assemblies of the denitrifying bacteria within a single genus, favoring their use as model organisms. Around 50 genes are required within a single bacterium to encode the core structures of the denitrification apparatus. Much of the denitrification process of gram-negative bacteria has been found confined to the periplasm, whereas the topology and enzymology of the gram-positive bacteria are less well established. The activation and enzymatic transformation of N oxides is based on the redox chemistry of Fe, Cu, and Mo. Biochemical breakthroughs have included the X-ray structures of the two types of respiratory nitrite reductases and the isolation of the novel enzymes nitric oxide reductase and nitrous oxide reductase, as well as their structural characterization by indirect spectroscopic means. This revealed unexpected relationships among denitrification enzymes and respiratory oxygen reductases. Denitrification is intimately related to fundamental cellular processes that include primary and secondary transport, protein translocation, cytochrome c biogenesis, anaerobic gene regulation, metalloprotein assembly, and the biosynthesis of the cofactors molybdopterin and heme D1. An important class of regulators for the anaerobic expression of the denitrification apparatus are transcription factors of the greater FNR family. Nitrate and nitric oxide, in addition to being respiratory substrates, have been identified as signaling molecules for the induction of distinct N oxide-metabolizing enzymes.

[36] HU H, CHEN D, HE J. Microbial regulation of terrestrial nitrous oxide formation: understanding the biological pathways for prediction of emission rates
FEMS Microbiology Reviews, 2015,39(5):729-749.
DOI:10.1093/femsre/fuv021URLPMID:25934121 [本文引用: 1]
The continuous increase of the greenhouse gas nitrous oxide (N2O) in the atmosphere due to increasing anthropogenic nitrogen input in agriculture has become a global concern. In recent years, identification of the microbial assemblages responsible for soil N2O production has substantially advanced with the development of molecular technologies and the discoveries of novel functional guilds and new types of metabolism. However, few practical tools are available to effectively reduce in situ soil N2O flux. Combating the negative impacts of increasing N2O fluxes poses considerable challenges and will be ineffective without successfully incorporating microbially regulated N2O processes into ecosystem modeling and mitigation strategies. Here, we synthesize the latest knowledge of (i) the key microbial pathways regulating N2O production and consumption processes in terrestrial ecosystems and the critical environmental factors influencing their occurrence, and (ii) the relative contributions of major biological pathways to soil N2O emissions by analyzing available natural isotopic signatures of N2O and by using stable isotope enrichment and inhibition techniques. We argue that it is urgently necessary to incorporate microbial traits into biogeochemical ecosystem modeling in order to increase the estimation reliability of N2O emissions. We further propose a molecular methodology oriented framework from gene to ecosystem scales for more robust prediction and mitigation of future N2O emissions.

[37] STANGE C F, SPOTT O, ARRIAGA H, MENéNDEZ S, ESTAVILLO J M, MERINO P. Use of the inverse abundance approach to identify the sources of NO and N₂O release from Spanish forest soils under oxic and hypoxic conditions
Soil Biology and Biochemistry, 2013,57:451-458.
DOI:10.1016/j.soilbio.2012.10.006URL [本文引用: 1]
Forest soils exhibit a variety of complex biochemical nitrogen (N) reactions in which nitric oxide (NO) and nitrous oxide (N2O) can be produced by coexisting processes that respond differently to the same environmental conditions. In general, two biochemical processes, (i) the oxidation of ammonia (nitrification) and (ii) the reduction of nitrate (denitrification), are known as the major sources of nitrogen oxides. Few reports indicated that a direct oxidation of soil organic N compounds (Norg) to NO and N2O may also be significant in soils.
A triplet N-15 tracer experiment (TTE) combined with an inverse abundance approach (IAA) was applied to quantify NO and N2O formation in soil related to different but simultaneously utilized soil N sources (ammonium, nitrate, and Norg). In addition, the impact of oxic and hypoxic conditions (21 and 2% v/v 02, respectively) on total soil NO/N2O release and source composition was studied. Experiments were conducted with soil samples from 5 different Basque forest stands (mature beech, young beech, mature pine, young pine, and new pine plantation).
The release rates of NO and N2O were higher in the soil samples from beech stands than in the samples from pine stands. The change from oxic to hypoxic conditions increased the NO release rate 2- to 14-fold and the N2O release rate 3.6- to 25-fold. The study suggests that, under oxic conditions, N2O formation based on Norg appears to be the dominant pathway of soil N2O production (48-76% to total N2O release). Under hypoxic conditions, the relative contribution of Norg significantly decreased, whereas its absolute contribution increased concomitantly. Denitrification was the dominant process of soil N2O release under hypoxic conditions and served as the major pathway of soil NO release under both oxic and hypoxic conditions (40 and 60% of total soil NO release, respectively).
We conclude that the individual contribution of different soil N pools to the total soil N gas release and the impact of environmental parameters (e.g., O-2 availability) are site-specific. Nonetheless, further research is required to elucidate the impact of forest stands on soil NO and N2O production, particularly N2O formation directly based on Norg transformation. (C) 2012 Elsevier Ltd.

[38] SPOTT O, RUSSOW R, STANGE C F. Formation of hybrid N₂O and hybrid N₂ due to codenitrification: First review of a barely considered process of microbially mediated N-nitrosation
Soil Biology and Biochemistry, 2011,43(10):1995-2011.
DOI:10.1016/j.soilbio.2011.06.014URL [本文引用: 1]
At the end of the 19th century an experimental study had already reported N gas production during microbial nitrate reduction, which significantly exceeded the amount of nitrate N supplied to the microorganism. The observed excess gas production was suggested to be caused by a reaction of nitrous acid (produced during microbial nitrate reduction) with amino acids contained in the nutrient solution. Since the 1980's a number of N-15 tracer experiments revealed that this biotic excess gas production was based on the formation of hybrid N2O and/or hybrid N-2. It was shown that the N N linkage forms due to a microbially mediated N-nitrosation reaction by which one N atom of nitrite or nitric oxide combines via a nitrosyl intermediate with one N atom of another N species (e.g., amino compound). Because of its cooccurrence with conventional denitrification this process was later on termed "codenitrification". Although the phenomenon of N2O and N-2 formation by codenitrification was recognised over a century ago its impact on global N cycling is still unclear today. Nonetheless, the present literature review reveals codenitrification as a potentially important process of biospheric N cycling since (i) most codenitrifying species are already known as typical denitrifiers (e.g., Pseudomonas sp., Fusarium sp. etc.) and (ii) codenitrification was already reported to occur within the three domains archaea, bacteria, and eukarya (kingdom fungi). Furthermore, the present literature suggests that codenitrification acts not only as an additional source of N gas formation due to a mobilisation of organic N by N-nitrosation, but also acts as an N immobilising process due to a bonding of inorganic N (e.g., from NO3- or NO2-) onto organic compounds due to e.g., N- or even C-nitrosation reactions. From this it can be concluded that N gas formation by codenitrification represents a sub-phenomenon of a variety of possible biotic nitrosation reactions. Moreover, the review reveals that biotic nitrosation also occurs among nitrifying species, even under aerobic conditions. Furthermore, recent studies support the assumption that even anaerobic ammonium oxidation (anammox) appears to be based on biotically mediated N-nitrosation. Therefore, we propose to introduce the term BioNitrosation, which includes all biotically mediated nitrosation reactions resulting either in N gas release or in N immobilisation, independently from the acting microbial species or the environmental conditions. (C) 2011 Elsevier Ltd.

[39] VAN CLEEMPUT O. Subsoils: chemo- and biological denitrification, N₂O and N₂ emissions
Nutrient Cycling in Agroecosystems, 1998,52:187-194.
DOI:10.1023/A:1009728125678URL [本文引用: 1]

[40] QU Z, WANG J, ALM?Y T, BAKKEN L R. Excessive use of nitrogen in Chinese agriculture results in high N₂O/(N₂O+N₂) product ratio of denitrification, primarily due to acidification of the soils
Global Change Biology, 2014,20(5):1685-1698.
DOI:10.1111/gcb.12461URL [本文引用: 1]
China is the world's largest producer and consumer of fertilizer N, and decades of overuse has caused nitrate leaching and possibly soil acidification. We hypothesized that this would enhance the soils' propensity to emit N2O from denitrification by reducing the expression of the enzyme N2O reductase. We investigated this by standardized oxic/anoxic incubations of soils from five long-term fertilization experiments in different regions of China. After adjusting the nitrate concentration to 2mM, we measured oxic respiration (R), potential denitrification (D), substrate-induced denitrification, and the denitrification product stoichiometry (NO, N2O, N-2). Soils with a history of high fertilizer N levels had high N2O/(N2O+N-2) ratios, but only in those field experiments where soil pH had been lowered by N fertilization. By comparing all soils, we found a strong negative correlation between pH and the N2O/(N2O+N-2) product ratio (r(2)=0.759, P<0.001). In contrast, the potential denitrification (D) was found to be a linear function of oxic respiration (R), and the ratio D/R was largely unaffected by soil pH. The immediate effect of liming acidified soils was lowered N2O/(N2O+N-2) ratios. The results provide evidence that soil pH has a marginal direct effect on potential denitrification, but that it is the master variable controlling the percentage of denitrified N emitted as N2O. It has been known for long that low pH may result in high N2O/(N2O+N-2) product ratios of denitrification, but our documentation of a pervasive pH-control of this ratio across soil types and management practices is new. The results are in good agreement with new understanding of how pH may interfere with the expression of N2O reductase. We argue that the management of soil pH should be high on the agenda for mitigating N2O emissions in the future, particularly for countries where ongoing intensification of plant production is likely to acidify the soils.

[41] SIX J, OGLE S M, CONANT R T, MOSIER A R, PAUSTIAN K. The potential to mitigate global warming with no-tillage management is only realized when practised in the long term
Global Change Biology, 2004,10(2):155-160.
DOI:10.1111/gcb.2004.10.issue-2URL [本文引用: 1]

[42] PIVA J T, DIECKOW J, BAYER C, ZANATTA J A, DE MORAES A, PAULETTI V, TOMAZI M, PERGHER M. No-till reduces global warming potential in a subtropical Ferralsol
Plant and Soil, 2012,361(1/2):359-373.
DOI:10.1007/s11104-012-1244-1URL [本文引用: 1]

[43] 邬磊. 稻田转菜地对生态系统碳平衡和温室气体排放的影响研究
[D]. 湖北: 华中农业大学, 2018.
[本文引用: 1]

WU L. Effects of land-use conversion from double-rice to vegetable cultivation on net ecosystem carbon budget and greenhouse gas emissions
[D]. Hubei: Huazhong Agricultural University, 2018. (in Chinese)
[本文引用: 1]