Simulation of greenhouse gas emission reduction years after the conversion of cropland into paddy field in southern China
ZHAOMiaomiao1,3,, SHAORui1, LIRenqiang1, YANGJilin2,3, XUMing1,3, 1. Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China2. State Key Laboratory of Resources and Environmental Information System, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China3. University of Chinese Academy of Sciences, Beijing 100049, China 通讯作者:通讯作者:徐明,男,河南平顶山人,博士,研究员,研究方向为资源环境与生态系统模拟。E-mail: mingxu@igsnrr.ac.cn 收稿日期:2017-11-7 修回日期:2019-03-6 网络出版日期:2019-07-25 版权声明:2019《资源科学》编辑部《资源科学》编辑部 基金资助:国家重点研发计划项目(2017YFA0604302) 作者简介: -->作者简介:赵苗苗,女,山东郓城人,博士研究生,研究方向为资源环境与生态系统模拟。E-mail: zhaomm@lreis.ac.cn
关键词:土地利用方式转变;温室气体;稻田;年限;轮作;排放通量;千烟洲 Abstract Agricultural production activities are one of the main sources of atmospheric greenhouse gases. Different crop cultivation systems and management methods will affect greenhouse gas emissions. There have been a lot of researches on the laws and control mechanisms of agricultural greenhouse gas emissions at home and abroad, but there are relatively few studies on the laws and influence mechanisms of greenhouse gas emissions. In this study, greenhouse gas fluxes new paddy fields (just converted from paddy fields to rice fields) in 2013-2016 and old paddy(which have been rice fields for the past 20 years) fields in 2016 as well as soil micro-meteorological and other physical and chemical properties were observed using a field plot experiment at the Qianyanzhou Ecological Station of the Chinese Academy Sciences in southern China. Then, seasonal and annual variation of greenhouse gas fluxes and the main factors that impacting greenhouse gas fluxes were analyzed. Based on the analysis, the dynamic changes of greenhouse gas emissions in rice fields are predicted. The results show that in the first four years after land-use conversion, CH4 emission fluxes in the new paddy fields were significantly lower than that in the old paddy fields, and annual emission increased with the extension of farming period, while the CH4 emission rate of old rice fields is not obvious, whereas the difference in emission of the greenhouse gases CO2 and N2O were not significant. Moreover, soil pH and the soil organic carbon content of new rice fields were lower than that of old paddy fields. The model simulation results show that shortening paddy field rotation (water-dry rotation) period (less than 7 years) can effectively reduce CH4 and total greenhouse gas emissions in paddy fields. The results suggest that using the CH4 emission coefficient of old rice fields may significantly overestimate CH4 emissions from new rice fields. This study may provide new insights for understanding the impact of land- use change on greenhouse gas emissions, and provide a basis for accurate estimation of regional agricultural greenhouse gas emissions and the development of emission reduction policies.
Keywords:land-use conversion;greenhouse gases;paddy;land-use years;rotation;flux;Qianyanzhou -->0 PDF (4283KB)元数据多维度评价相关文章收藏文章 本文引用格式导出EndNoteRisBibtex收藏本文--> 赵苗苗, 邵蕊, 李仁强, 杨吉林, 徐明. 中国南方旱田转水田后温室气体减排年限预测[J]. 资源科学, 2019, 41(7): 1286-1294 https://doi.org/10.18402/resci.2019.07.09 ZHAOMiaomiao, SHAORui, LIRenqiang, YANGJilin, XUMing. Simulation of greenhouse gas emission reduction years after the conversion of cropland into paddy field in southern China[J]. RESOURCES SCIENCE, 2019, 41(7): 1286-1294 https://doi.org/10.18402/resci.2019.07.09
结合千烟洲站实际土地利用类型,并考虑到转换的可行性,旱地转稻田后对温室气体排放的影响研究选取旱作油茶园进行土地利用转换。试验样地布设于2013年1月开始施行,经过3年的野外观测与数据分析,发现土地利用方式转变后的新稻田温室气体综合增温效应(稻田3种主要温室气体CH4,CO2,N2O排放按相对分子质量换算成CO2之后的总增温效应)[31,32]显著低于同地区的老稻田[31,32,33]。为了排除土壤类型、气候、人为管理措施等其他因素对稻田温室气体排放的影响,从2016年1月开始,对实验样地附近一块13年的老稻田布设实验,进行温室气体排放通量观测,两者采用相同的水肥管理模式。稻田样方大小10 m×10 m,从移栽到收获,早稻生长期约85天左右,晚稻约96天左右。在水稻移栽前2~3天对实验样地进行蓄水、翻耕,然后施入底肥(复合肥72 kg N/hm2);水稻移栽10天左右施追肥(化肥108 kg N/hm2)。水稻淹水期持续约30天,包括整个幼苗及分蘖期,随后进入烤田期持续约20天,最后间歇灌溉持续到水稻收获。水稻收获采取人工收割的方式,除根部之外,粮食和秸秆均移出稻田生态系统。
3.1.1 稻田温室气体排放通量 如图1、图2所示,研究期间,随水稻植株的生长,稻田CH4温室气体排放通量呈现出明显的年际和季节变化,主要排放集中在淹水期即每年早稻季4月30日—5月30日、晚稻季7月30日—8月30日,非淹水期和冬闲季CH4通量较低。水稻移栽后,CH4排放通量逐渐增加,在移栽10~25天时达到最大值;晒田及成熟期,水稻土壤含水量下降,新老稻田CH4排放通量均急剧下降。老稻田2016年CH4排放通量为1.01±0.07 kg C/(hm2·d),年累积排放量为368.78 kg C/hm2(图1)。新稻田CH4排放通量变化范围为-0.04~7.13 kg C/(hm2·d),新稻田多年平均累积排放量为204.11 kg C/hm2。2013—2016年新稻田CH4年平均排放通量随耕作年限延长逐年增加,依次为0.24±0.01、0.48±0.03、0.63±0.01和0.87±0.03 kg C/(hm2·d)(图2)。 显示原图|下载原图ZIP|生成PPT 图1老稻田CH4通量与土壤湿度 -->Figure 1CH4 fluxes and soil moisture of old paddy during the study period -->
显示原图|下载原图ZIP|生成PPT 图2新稻田CH4通量与土壤湿度 -->Figure 2CH4 fluxes and soil moisture of new paddy during the study period -->
如图3、图4所示,稻田生态系统总呼吸能够表征水稻的生长状况,CO2排放呈现出明显的季节变化规律,与温度变化趋势基本一致,表现为生长季(4—10月)高于非生长季(11月—次年4月)。老稻田2016年CO2排放通量为39.19±2.07 kg C/(hm2·d),年累积排放量为14306.01 kg C/hm2(图3)。新稻田CO2排放通量变化范围为2.55~129.81 kg C/(hm2·d),新水稻田多年平均累积排放量为11563.20 kg C/hm2。2013—2016年新稻田CO2年平均排放通量依次为34.50±3.41、36.00±5.43、28.26±2.51和27.96±3.79 kg C/(hm2·d)(图4)。新稻田与老稻田生态系统总呼吸差异不显著。 显示原图|下载原图ZIP|生成PPT 图3老稻田CO2通量与温度 -->Figure 3CO2 fluxes of old paddy during the study period -->
显示原图|下载原图ZIP|生成PPT 图4新稻田CO2通量与温度 -->Figure 4CO2 fluxes of new paddy during the study period -->
稻田N2O的排放通量较低,N2O排放峰值通常出现在施肥后1周内(即每年4月30号、5月10号、7月30号和8月10号左右),同时突发性强降水对N2O排放有激发作用,水稻生长季N2O排放明显高于非生长季。老稻田2016年N2O排放通量为0.0064 kg N/(hm2·d),年累积排放量为2.34 kg N/hm2(图5)。新稻田N2O排放通量变化范围为 -0.0062~0.0493 kg N/(hm2·d),新水稻田多年平均累积排放量为2.37 kg N/hm2。2013—2016年新稻田N2O年平均排放通量依次为0.0073、0.0036、0.0086和0.0065 kg N/(hm2·d)(图6)。新稻田与老稻田N2O排放通量差异不显著。 显示原图|下载原图ZIP|生成PPT 图5老稻田N2O通量与降水量 -->Figure 5N2O fluxes of old paddy during the study period -->
显示原图|下载原图ZIP|生成PPT 图6新稻田N2O通量与降水量 -->Figure 6N2O fluxes of new paddy during the study period -->
3.1.2 稻田温室气体排放影响因素 稻田土壤温室气体排放的变异与温度、水分条件、SOC和人为管理措施等有关。本研究中测定的新老稻田温室气体排放影响因素主要包括:年平均土壤温度、年平均土壤湿度、土壤pH、SOC含量和水稻生物量等(表1)。 Table 1 表1 表1研究期间土壤温湿度、pH、SOC以及生物量参数 Table 1Climatic factors, soil properties, and rice biomass during the study period
稻田
年份
年平均土壤温度/℃
年平均土壤湿度/%
土壤pH
SOC/(g C/kg土壤)
水稻生物量/(t干物质/年)
新稻田
2013
19.7±0.2
34.26±0.15
4.93±0.01
5.77±0.01
22.61±2.29
2014
19.9±0.1
33.26±0.34
5.01±0.02
5.99±0.02
20.53±1.38
2015
19.9±0.1
33.08±0.45
5.11±0.03
6.03±0.03
21.97±2.08
2016
20.0±0.2
34.01±0.16
5.22±0.03
6.24±0.04
20.81±1.01
老稻田
2016
19.8±0.2
34.52±0.21
5.32±0.23
9.56±0.31
20.45±1.09
新窗口打开 其中,新老稻田的年平均土壤温度、年平均土壤湿度及水稻生物量相差不大。新稻田的土壤pH(均值为5.07±0.03)略低于老稻田,SOC含量(均值为6.01±0.03 g C/kg土壤)明显低于老稻田,且随土地利用方式转变后的耕作年限延长逐渐增加。
3.2 水稻温室气体减排轮作年限预测
研究表明,常年种植的老稻田其CH4排放量几乎不随种植年限的变化而变化[31,32],土地利用变化能有效地降低水稻田土壤温室气体的排放,因此本文认为土地利用方式转变之后的新水稻增温效应达到与老水稻增温效应一致的水平需要一定的转换时间。为预测转换时间,本文对新老稻田CH4的年总排放量曲线采用线性、多项式、对数和米氏方程4种方式进行拟合,如图7所示。 显示原图|下载原图ZIP|生成PPT 图7不同方法预测水稻温室气体减排年限 -->Figure 7Greenhouse gas emission reduction years of rice simulated by different methods -->
4种拟合方程的R2均较高,此时考虑稻田温室气体初始时增加,然后趋于稳定的排放规律,且本着方程尽可能简单化的原则,选择米氏方程(图7d)来模拟新稻田CH4的排放。公式为: (3) 式中:x为转换年数;y为新稻田CH4排放通量;a为老稻田CH4排放通量;k为半饱和常数,即CH4排放通量新稻田与老稻田一致需要的年数的一半。 结合CH4排放数据,从公式可以得到a=368.78 kg C/hm2时,k=3.2。所以土地利用转换后的新稻田大约需要7年的时间才能达到老稻田温室气体排放通量的水平。
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