Effects of dew on eco-physiological traits and leaf structures of Leymus chinensis and Agropyron cristatum grown under drought stress
CENYu通讯作者:
收稿日期:2017-05-3
接受日期:2017-10-16
网络出版日期:2017-11-10
版权声明:2017植物生态学报编辑部本文是遵循CCAL协议的开放存取期刊，引用请务必标明出处。
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Abstract
Methods Four treatments (no dew, three times dew and five times dew per week under drought stress, and well-watering) were designed to examine leaf relative water content, water potential, net photosynthetic rate, water use efficiency, biomass, and leaf structures of L. chinensis and A. cristatum.
Important findings There was a significant increase in the relative water content and water potential by simulated dew increase for two plants species under drought stress (p < 0.05). For A. cristatum, simulated dew increase significantly enhanced the net photosynthetic rate, stomatal conductance, and transpiration rate of plants under drought stress (p < 0.05). On the other hand, there was no significant difference in the stomatal conductance and transpiration rate for L. chinensis among treatments. Simulated dew increase improved the aboveground biomass and root biomass of two species. The ratio of yellow leaves to the total leaves was decreased by simulated dew increase for two species. Dew increase also protected leaf structures against the drought stress, suggesting that the dew increase can slow down the death process of leaves resulted from drought stress. Therefore, the study demonstrated that dew increased the available water for the leaves of L. chinensis and A. cristatum grown in the drought stress and thus had positive effects on the photosynthesis, water physiology and plant development.
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凝结水是指大气或土壤孔隙中的水汽在地面或物体表面温度低至露点时凝结生成的液态水(冯起和高前兆, 1995; 庄艳丽和赵文智, 2008)。在干旱、半干旱区, 凝结水作为除降水以外最主要的可持续的补充水源, 对植物、动物以及人类的生命活动具有重要的、不可替代的生态作用(Kidron et al., 2000; Munné-Bosch, 2010; Hill et al., 2015; Tomaszkiewicz et al., 2015)。目前国外对凝结水的研究比较广泛深入, 探讨了多种植物叶片对凝结水的吸收利用, 比如对地中海乡土常绿灌木Lavendula stoechas的光合作用、气孔导度以及CO2同化率等生理指标的研究发现, 该植物的叶片能够吸收并利用凝结水(Munné-Bosch et al., 1999); Martin和von Willert (2000)对非洲西南部大西洋沿岸干旱区的纳米布沙漠46种景天科植物的调查发现其中有27种植物能够吸收叶片表面的凝结水; Limm等(2009)研究发现红树林中80%的优势种可以通过叶片吸收凝结水; 另有研究发现需水量少的地衣、苔藓、附生植物等同样可以吸收利用凝结水(Eller et al., 2013; Gotsch et al., 2014)。国内关于凝结水的研究尚处于起步阶段, 有少数研究者探讨植物对凝结水的吸收与利用, 如郑玉龙和冯玉龙(2006)通过蒸馏喷雾法模拟凝结水发现西双版纳地区的10种附生植物和非附生植物的叶片都能够吸收凝结水; 庄艳丽和赵文智(2009, 2010)发现干旱条件下, 凝结水对一年生荒漠植物雾冰藜(Bassia dasyphylla)的水分关系、光合速率、气孔导度等生理特性具有重要作用。在全球变化大背景下, 干旱的区域和面积不断地扩展, 凝结水对全球不同生境类型的生态系统, 尤其是干旱区生态系统的意义越来越重要(Rahimi et al., 2013)。
基于国内外对凝结水的研究进展, 本研究提出以下两个科学问题, 凝结水是否可以缓解干旱胁迫对植物生理和生长的影响?凝结水是否可以减缓和修复植物叶片由于干旱造成的破损?基于这样的科学问题, 本研究选取内蒙古半干旱区草原的优势植物种羊草(Leymus chinensis)和冰草(Agropyron cristatum)为研究对象, 通过模拟凝结水的方法来探讨植物叶片对凝结水的吸收和利用, 研究凝结水对干旱胁迫下植物碳同化作用、水分生理和生长的影响, 为深入了解全球变化背景下植物对干旱胁迫的适应策略提供理论依据。
1 材料和方法
1.1 试验地概况
试验在中国科学院植物研究所内的大型可控环境条件的玻璃温室中进行, 该温室可以自动调控温度、湿度以及光照等环境条件。试验期间, 温室内放置了一个长×宽×高为5 m × 1.5 m × 1 m的暗室, 暗室内放置两个超声波加湿器来模拟凝结水的发生, 并且使用温湿度探头(Onset Computer Corporation, Bourne, USA)同步记录暗室内外的温度和湿度等气象数据。1.2 试验物种选择
羊草和冰草都属于禾本科植物, 因其具有较强的耐寒、耐旱性, 是干旱半干旱草原生态系统中重要的优势植物种, 分布广泛。2015年8月在内蒙古浑善达克沙地收集这两种植物的成熟种子。1.3 试验方法
1.3.1 试验设计试验于2016年3月下旬至7月上旬进行。3月下旬对羊草和冰草种子进行发芽育苗, 待幼苗生长2周左右, 高度达到约10 cm后移栽至下口直径为13 cm、 上口直径为18 cm、高为18 cm的花盆中, 花盆中放置草炭土与蛭石以体积比3:1混合后的土壤, 每盆移栽一株植物, 两种植物各40盆。试验前期, 所有植物处理均保持一致, 在此期间用便携式土壤水分仪(HH2- ML3, Delta-T, Cambridge, UK)测定土壤最大持水量。待移栽后的植物生长8周, 选择生长状态基本一致、长势良好的羊草和冰草各28盆进行试验。试验开始初期, 先对所有植物进行2周的干旱处理控制土壤含水量, 使土壤含水量维持在5%-6% (土壤最大持水量的11%左右), 之后对干旱处理的植物进行模拟凝结水的试验。试验设置4种处理, 即干旱胁迫下无凝结水发生(W0)、干旱每周发生3次凝结水(W3)、干旱每周发生5次凝结水(W5)以及正常浇水(W), 每种处理7个重复。正常浇水(W), 保持土壤含水量约为18% (土壤最大持水量的30%左右), 不发生凝结水。试验共进行4周。
试验中凝结水是在暗室中通过超声波加湿器来产生。根据野外试验结果表明, 浑善达克沙地草地凝结水通常在20:00左右发生, 到22:00左右凝结水量开始显著增加, 直到第二日6:00-7:00达到最大值(Wang et al., 2017), 因此在室内试验中选择该时间段为凝结水喷施的时间。处理日的夜间22:00开始产生凝结水, 直到第二天早晨6:00, 共持续8 h。在凝结水发生期间, 用空气温度和湿度探头同步记录温室中暗室内外的温度和湿度(图1)。数据表明, 试验期间暗室内大气相对湿度保持在95%-100%, 暗室内外的温度差值小于1 ℃, 所以可以忽略温度差异对试验结果产生的影响。凝结水发生期间为防止水分流入土壤, 每个花盆用锡纸包裹覆盖。在试验进行的第三周选择晴朗天气的上午测定叶片的净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)以及水势(Ψleaf), 连续测定两天; 相对含水量(RWC)的测定从试验开始前第一次测定, 试验第二周和第四周选取晴朗天气的上午测定, 共测定3次。试验结束之前, 计数每株植物叶片中黄叶数和绿叶数, 并取W0、W3以及W处理的植物叶片进行电镜扫描观察叶片的表面结构。待以上指标测定完毕, 将植株收获, 分别测定地上和地下生物量。
显示原图|下载原图ZIP|生成PPT图1试验期间暗室内外的温度和湿度动态。
-->Fig. 1Dynamics of temperature and humidity in and outside of the dark chamber during the experiment.
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1.3.2 测定方法
1.3.2.1 叶片相对含水量(RWC)和叶片水势(Ψleaf)的测定 RWC和Ψleaf的测定时间为10:00左右, 待叶片上的凝结水完全消退后, 采集植物成熟叶片, 装入手提冰箱里, 迅速带回实验室进行测定。Ψleaf用WP4C露点水势仪(LI-COR, Lincoln, USA)测定。RWC用称质量法测定, 取完全展开的成熟叶片2-3片, 称其鲜质量(M), 之后在蒸馏水中浸泡24 h使其达到恒质量后测定叶片的饱和鲜质量(M0), 再将植物叶片置于烘箱中在65 ℃下烘48 h至恒质量后称其干质量(M1), 用以下公式计算相对含水量。
RWC = (M - M1) / (M0 - M1) × 100%
1.3.2.2 净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)的测定 Pn、Gs和Tr采用LI-6400便携式光合作用测定系统(LI-COR, Lincoln, USA)选择红蓝光源来测定。每株植物选择3片完全展开的成熟叶片于每个测定日10:00左右测定, 每个处理7个重复。用Pn与Tr之比表示植物水分利用效率(WUE)。
1.3.2.3 生物量的测定 在试验进行4周后, 对羊草和冰草4个处理的每株植物分别统计其黄叶数与绿叶数, 计算黄叶数与总叶数的比值。之后将两种植物4个处理的每个重复分别进行收获, 花盆中取出植物时尽量减少对根的损失, 将地上部分剪下, 并对根进行冲洗, 然后将每株植物的地上和地下部分分别在65 ℃下烘48 h至恒质量, 称质量后得到地上生物量和地下生物量干质量。
1.3.2.4 叶片表面结构 对W0、W3以及W三个处理下的成熟叶片进行取样, 用刀片将叶片切成约2 mm × 2 mm的小块(切块时要避开叶片的中脉, 以免影响电镜下的观察), 然后将切成小块的叶片放入FAA固定液中固定, 保存3天, 之后将固定的小叶片取出用不同浓度的酒精和乙酸异戊酯进行脱水、置换, 然后用CO2临界点干燥法进行干燥、粘台、镀膜后在S-4800日立场发射扫描电镜(Hitachi, Tokyo, Japan)下进行观察和拍摄。
1.4 数据处理
数据前期整理使用Excel 2016, 对Pn、Gs、Tr、Ψleaf以及生物量等的测定结果进行汇总, 之后用SPSS 22.0软件对不同处理下的植物光合指标、水分生理指标和生长指标的数据进行单因素方差分析, 显著性水平α = 0.05。作图采用Excel 2016。2 结果和分析
2.1 凝结水对叶片RWC和Ψleaf的影响
干旱胁迫下, 两种植物叶片RWC都显著低于正常浇水处理(p < 0.05), 且干旱胁迫的时间越长, 叶片RWC越低; 凝结水发生的频率越高, RWC降低得越少。试验第四周, 羊草W3 (50%)和W5 (54%)处理与W0 (46%)相比, 叶片RWC分别提高了8%和16%, 处理间差异不显著(p > 0.05)(图2A); 冰草W3 (47%)和W5 (57%)处理与W0 (33%)相比, 叶片RWC分别提高了41%和71%, 差异显著(p < 0.05) (图2B)。
显示原图|下载原图ZIP|生成PPT图2凝结水对羊草和冰草叶片相对含水量(RWC)的影响(平均值±标准误差)。W0, 干旱胁迫无凝结水; W3, 干旱胁迫每周3次凝结水; W5, 干旱胁迫每周5次凝结水; W, 正常浇水无凝结水。
-->Fig. 2Effects of dew increase on leave relative water content (RWC) of Leymus chinensis and Agropyron cristatum (mean ± SE). W0, no dew under drought; W3, simulated dew increase three times a week under drought; W5, simulated dew increase five times a week under drought; W, well watering no simulated dew.
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统计分析数据表明, 与W处理相比, 干旱胁迫显著降低了羊草和冰草的Ψleaf (p < 0.05); 干旱胁迫下, 凝结水可以提高两种植物的Ψleaf, 但是与凝结水发生的频率有关,凝结水发生次数越多,叶片水势提高也越多, 越能有效地减缓植物受到的干旱胁迫。对于羊草, 处理W3 (-2.51 MPa)和W5 (-2.27 MPa)与W0 (-2.88 MPa)相比, Ψleaf显著提高了13%和21% (p < 0.05), 但是W3和W5处理间差异不显著; 冰草W3 (-1.82 MPa)和W5 (-1.67 MPa)处理与W0 (-2.13 MPa)相比, Ψleaf分别提高了14%和22%, 其中, W5处理与W0达到显著差异(p < 0.05) (图3)。
显示原图|下载原图ZIP|生成PPT图3凝结水对羊草和冰草叶片水势(Ψleaf)的影响(平均值±标准误差)。W0, 干旱胁迫无凝结水; W3, 干旱胁迫每周3次凝结水; W5, 干旱胁迫每周5次凝结水; W, 正常浇水无凝结水。2.2 凝结水对植物光合生理的影响
-->Fig. 3Effects of dew increase on leaf water potential (Ψleaf) of Leymus chinensis and Agropyron cristatum (mean ± SE). W0, no dew under drought; W3, simulated dew increase three times a week under drought; W5, simulated dew increase five times a week under drought; W, well watering no simulated dew
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处理W0、W3以及W5与W相比, 羊草和冰草的Pn、Gs和Tr都显著降低(p < 0.05)。对于冰草, 干旱胁迫下, 凝结水对其Pn、Gs与Tr都有显著提高(p < 0.05); 凝结水发生的频率越高, Pn、Gs与Tr越大, 处理W3和W5与W0相比, Pn分别提高了0.58倍和1.73倍, Gs分别提高了0.73倍和1.44倍, 差异显著(p < 0.05)。干旱胁迫下, 羊草Pn对凝结水的响应趋势与冰草类似, 处理W3和W5与W0相比, Pn分别提高了0.37倍和1.33倍, W3和W0处理间差异不显著, 其他处理差异均显著(p < 0.05); 干旱胁迫下, 羊草的Gs和Tr随凝结水的变化基本没有提高, 这一点与冰草的变化趋势不同(图4A、4B、4C)。
显示原图|下载原图ZIP|生成PPT图4凝结水对羊草(●)和冰草(○)净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)与水分利用效率(WUE)的影响(平均值±标准误差)。W0, 干旱胁迫无凝结水; W3, 干旱胁迫每周3次凝结水; W5, 干旱胁迫每周5次凝结水; W, 正常浇水无凝结水。
-->Fig. 4Effects of dew increase on photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) and water use efficiency (WUE) of Leymus chinensis (●) and Agropyron cristatum (○) (mean ± SE). W0, no dew under drought; W3, simulated dew increase three times a week under drought; W5, simulated dew increase five times a week under drought; W, well watering no simulated dew.
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显示原图|下载原图ZIP|生成PPT图5凝结水对羊草(A)和冰草(B)地上和地下生物量的影响(平均值±标准误差)。W0, 干旱胁迫无凝结水; W3, 干旱胁迫每周3次凝结水; W5, 干旱胁迫每周5次凝结水; W, 正常浇水无凝结水。同种植物不同小写字母表示在p < 0.05水平上各处理间差异显著。
-->Fig. 5Effects of dew increase on biomass of Leymus chinensis (A) and Agropyron cristatum (B) (mean ± SE). W0, no dew under drought; W3, simulated dew increase three times a week under drought; W5, simulated dew increase five times a week under drought; W, well watering no simulated dew. Different lowercase letters indicate the difference is significant among the treatments at p < 0.05 level.
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干旱胁迫下, 两种植物WUE对凝结水的响应趋势不同(图4D)。凝结水发生频率的增加显著提高了羊草的WUE, 其中W5处理下的WUE最高; 冰草的WUE对凝结水发生频率的增加变化不显著。
2.3 凝结水对生物量的影响
与W处理相比,干旱胁迫显著降低了两种植物的地上生物量和根系生物量(p < 0.05); 处理W3和W5与W0相比, 羊草的地上生物量分别提高了9%和12%, 冰草的地上生物量分别提高6%和14%, 差异不显著(p > 0.05)。干旱胁迫下, 处理W3和W5与W0相比, 羊草的根系生物量分别提高了20%和23% (p < 0.05); 而凝结水的发生对冰草的根系生物量影响不显著(p > 0.05)。
2.4 凝结水对黄叶数与总叶数的影响
与正常浇水处理相比, 干旱胁迫下, 羊草和冰草的总叶数和绿叶数逐渐下降, 黄叶数逐渐增加(图6)。干旱胁迫下, 随着凝结水发生频率的提高, 植株总叶数和绿叶数增加, 而黄叶数减少, 最终导致黄叶数与总叶数的比值有所降低。对于羊草, 处理W3 (35%)和W5 (32%)与W0 (37%)相比, 黄叶数与总叶数的比值分别降低了5%和14% (p > 0.05); 对于冰草, 处理W3 (26%)和W5 (21%)与W0 (31%)相比, 黄叶数与总叶数的比值分别降低了16%和32%, W5和W0处理间差异显著(p < 0.05), 其他各处理间差异不显著。
显示原图|下载原图ZIP|生成PPT图6凝结水对羊草和冰草黄叶数与总叶数比值的影响(平均值±标准误差)。W0, 干旱胁迫无凝结水; W3, 干旱胁迫每周3次凝结水; W5, 干旱胁迫每周5次凝结水; W, 正常浇水无凝结水。同种植物不同小写字母表示在p < 0.05水平上各处理间差异显著。
-->Fig. 6Effects of dew increase on the ratio of yellow leaves to total leaves of Leymus chinensis and Agropyron cristatum (mean ± SE). W0, no dew under drought; W3, simulated dew increase three times a week under drought; W5, simulated dew increase five times a week under drought; W, well watering no simulated dew. Diffferent lower case letters indicate the difference is significant among the treatments at p < 0.05 level.
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2.5 凝结水对叶片表面结构的影响
在电镜下观察羊草和冰草的叶片表面结构发现, W处理下, 两种植物的叶片表面结构光滑、完整, 可以清晰地观察到叶片表面的气孔、毛状突起等(图7A、7D); W0处理下, 两种植物叶片表面粗糙, 有不同程度的损伤(图7B、7E), 且观察发现羊草的叶片表面气孔下陷, 冰草的叶片表面毛状突起减少, 两种植物是通过不同的保护措施来减少水分蒸发并降低由于干旱缺水造成的叶片表面破坏; W3处理下, 羊草和冰草的叶片表面仍有不同程度的损伤(图7C、7F), 但是相对于W0处理, 叶片表面破损程度大大减小, 说明干旱胁迫下, 凝结水的发生对植物叶片表面有一定的保护作用, 凝结水可以有效地缓解干旱对植物叶片表面造成的损伤。
显示原图|下载原图ZIP|生成PPT图7凝结水对羊草和冰草叶片表面结构的影响。A、B、C分别是羊草W、W0以及W3处理的叶片表面结构电镜扫描图; D、E、F分别是冰草W、W0以及W3处理的叶片表面结构电镜扫描图。W0, 干旱胁迫无凝结水; W3, 干旱胁迫每周3次凝结水; W, 正常浇水无凝结水。
-->Fig. 7Effects of dew increase on leaf structures of Leymus chinensis and Agropyron cristatum. A, B and C were TEM micrographs of the leaf structures for Leymus chinensis at treatments of W, W0 and W3, respectively. D, E and F were TEM micrographs of the leaf structures for Agropyron cristatum at treatments of W, W0 and W3, respectively. W0, no dew under drought; W3, simulated dew increase three times a week under drought; W, well watering no simulated dew.
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3 讨论
研究者在不同生态系统中对凝结水是否能够补充植物生长所需水分进行的研究已经证实, 地中海气候区的植物、热带雨林植物、针叶树、需水量少的地衣、苔藓以及附生植物都可以吸收叶片表面的凝结水来补充植物生长过程中对水分的需求。早期的研究发现, 凝结水的发生可以减弱甚至避免干旱胁迫下植物光合速率的下降(Grammatikopoulus & Manetas, 1994); 凝结水可以提高干旱胁迫下Melissa officinalis的含水量, 并且对受到干旱胁迫的植物代谢有重要的恢复作用(Munné-Bosch & Alegre, 1999)。并且Munné-Bosch等(1999)在模拟凝结水的研究中发现, 干旱胁迫下, 凝结水发生3天和6天后, Melissa offuinalis的水势分别提高了18%和76%。Limm等(2009)的研究证实, Sequoia sempervirens的叶片可以通过吸收凝结水来减轻植株受到的水分胁迫, 并且使叶片的相对含水量增加了2%-11%; Zhuang和Sophia (2012)的研究发现, 凝结水的发生增加了雾冰藜(Bassia dasyphylla)枝条的相对含水量、水势以及总生物量, 并且可以使叶片的气孔导度和光合速率达到干旱胁迫下的最大值。我们的研究表明, 干旱胁迫下, 每周发生3次和5次凝结水与无凝结水处理相比, 羊草的叶片相对含水量分别提高了8%和16%, 冰草的叶片相对含水量分别提高了41%和71%; 相应地, 相同处理下羊草的叶水势分别提高了13%和21%, 冰草的叶水势分别提高了14%和22%, 这一点与前人的研究结果类似, 表明凝结水的发生可以适当地缓解植物因干旱胁迫导致的叶片水分亏缺状况。羊草和冰草相比, 干旱胁迫下, 叶水势随凝结水发生的变化趋势基本一致; 而在相对含水量方面, 冰草叶片含水量变化受到凝结水影响较大, 说明冰草吸收的这些凝结水主要是用来提高碳同化等代谢作用, 而不是用来维持水细胞膨压, 这一点可以通过冰草净光合速率、气孔导度和蒸腾速率都显著增加得以证实; 与冰草不同的是, 羊草的气孔导度和蒸腾速率随凝结水的发生没有显著提高, 但是水分利用效率变化显著。我们的研究发现, 干旱胁迫下, 凝结水对羊草和冰草光合生理影响不同, 表明两种植物是通过不同的调节机制来维持体内的水分, 保持细胞内环境的相对稳定, 羊草水分利用效率的提高表现出更强的抗旱性, 而冰草气孔导度和蒸腾速率的提高可以更好地吸收凝结水, 更好地缓解干旱胁迫造成的大量缺水。本试验测定的净光合速率和气孔导度都低于野外自然状态下羊草和冰草的净光合速率和气孔导度,主要是由于温室的光照以及花盆种植的影响, 但是这种条件对试验中所有植物的影响是一致的, 所以并不影响试验结果。观察羊草和冰草叶片的电镜扫描图发现, 凝结水对叶片表面结构有一定的保护作用。本研究表明, 干旱胁迫下, 每周发生3次凝结水和每周发生5次凝结水与无凝结水处理相比, 羊草的地上生物量分别提高了9%和12%, 冰草的地上生物量分别提高了6%和14%; 羊草的根系生物量分别提高了20%和23%, 冰草的根系生物量分别提高了3%和9%, 凝结水对两种植物生物量影响的变化趋势与前人的研究结果一致(Boucher et al., 1995; 庄艳丽和赵文智, 2009, 2010)。羊草和冰草相比, 在地上生物量和根系生物量方面都有相对较大比例的提高, 而在气孔导度和蒸腾速率方面没有显著的变化, 充分地表明了羊草和冰草两个物种之间具有不同的干旱适应策略。干旱胁迫下, 凝结水的发生虽然增加了冰草的净光合速率和气孔导度, 但是光合作用积累的生物量运输以及分配会受到水分的限制。在相同水分胁迫下, 羊草光合产物传输到根部的生理过程受到的影响较小。干旱胁迫下, 羊草主要通过调节气孔导度降低蒸腾失水的过程保持体内细胞水分的相对稳定; 而冰草在干旱胁迫下, 只要有少量凝结水发生, 就可以吸收利用来维持体内水分的相对稳定。羊草和冰草生物量对凝结水的响应说明, 干旱胁迫下, 羊草和冰草都能够吸收利用凝结水, 提高光合和水分生理代谢效率, 进而促进其生物量的积累。本研究发现, 干旱胁迫下, 羊草和冰草的总叶数和绿叶数逐渐下降, 黄叶数逐渐增加, 随着凝结水发生频率的提高, 植株总叶数和绿叶数增加, 而黄叶数减少, 最终导致黄叶数与总叶数的比值有所降低。Duvdevani (1964)在野外研究豆类、黄瓜(Cucumis sativus)、玉米(Zea mays)等发现凝结水的发生不仅可以增加植物的果实数目与质量, 同时可以增加植物的绿叶数。本研究表明植物对凝结水的响应因物种不同而差异较大, 而且不同物种对凝结水的响应策略与物种本身的抗逆性有很大关系。
4 结论
通过研究干旱胁迫下羊草和冰草生理生态特征和叶片表面结构对凝结水的响应, 可以得出以下结论:(1)干旱胁迫下, 羊草和冰草的叶片可以吸收并利用凝结水; 植物对凝结水的响应因物种不同而差异较大。
(2)干旱胁迫下, 凝结水的发生可以提高羊草和冰草的叶片相对含水量和叶水势。每周发生3次凝结水和5次凝结水与无凝结水处理相比, 羊草的叶片相对含水量分别提高了8%和16%, 冰草的叶片相对含水量分别提高了41%和71%; 羊草的叶水势分别提高了13%和21%, 冰草的叶水势分别提高了14%和22%。
(3)干旱胁迫下, 凝结水显著地提高了冰草的净光合速率、气孔导度和蒸腾速率; 而羊草的气孔导度和蒸腾速率随凝结水的变化不显著。
(4)干旱胁迫下, 凝结水的发生可以减缓植物叶片衰老变黄的速率, 并且对植物叶片表面结构的完整性有一定的保护和修复作用。
The authors have declared that no competing interests exist.
作者声明没有竞争性利益冲突.
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| [1] | . We investigated the effects of foliar absorption of dew by eastern white pine (Pinus strobus L.) seedlings on midday shoot water potential, as well as on other water relations variables and growth. Two-year-old container-grown eastern white pine seedlings were subjected to contrasting watering regimes (normal and deficient) and three frequencies of artificial dew (none, once and three times per week) for 10 weeks in a greenhouse. Midday shoot water potential was measured on four occasions during the study. Other water relations variables (relative water content, stomatal conductance, pressure-volume curves) and growth (hypocotyl diameter, aboveground dry mass, root dry mass) were also measured. Artificial dew significantly increased shoot water potential, stomatal conductance and seedling root growth, with greater responses observed for seedlings subjected to a deficient watering regime than for well-watered seedlings. Because dew can be a frequent microclimatic event in some areas, this finding has practical implications for field studies of water relations of eastern white pine and possibly of other coniferous species. |
| [2] | . An abstract is unavailable. This article is available as a PDF only. |
| [3] | . |
| [4] | . . |
| [5] | . The ecophysiology of tropical montane cloud forest (TMCF) trees is influenced by crown-level microclimate factors including regular mist/fog water inputs, and large variations in evaporative demand, which in turn can significantly impact water balance. We investigated the effect of such microclimatic factors on canopy ecophysiology and branch-level water balance in the dry season of a seasonal TMCF in Veracruz, Mexico, by quantifying both water inputs (via foliar uptake, FU) and outputs (day- and night-time transpiration, NT). Measurements of sap flow, stomatal conductance, leaf water potential and pressure–volume relations were obtained in Quercus lanceifolia, a canopy-dominant tree species. Our results indicate that FU occurred 34% of the time and led to the recovery of 9% (2465±659.165L) of all the dry-season water transpired from individual branches. Capacity for FU was independently verified for seven additional common tree species. NT accounted for approximately 17% (4665L) of dry-season water loss. There was a strong correlation between FU and the duration of leaf wetness events (fog and/or rain), as well as between NT and the night-time vapour pressure deficit. Our results show the clear importance of fog and NT for the canopy water relations of Q.65lanceifolia. |
| [6] | . |
| [7] | . We investigated the possible use of dew as a water source for three desert plant species native to the Negev Desert: an annual Salsola inermis , and two perennials Artemisia sieberi and Haloxylon scoparium, with different rooting depths of 15, 30 and 9002cm, respectively. We quantified dew-water inputs and used stable isotope analyses to determine the proportion of dew as compared to the proportion of soil water each species utilized. Dew was isotopically enriched (δD values ranged from 6125 to 502‰), relative to rainfall with δD values that ranged from 6140 to 612002‰ and relative to soil water with δD values that ranged from 6165 to 613502‰. Using a two-source isotope mixing model, we found that S. inermis, A. sieberi and H. scoparium used, on average, 56, 63 and 4602% of their water from dewfall, respectively. Our results suggest that dew-water utilization by Negev Desert plants is highly significant ecologically and thus may be more common than previously thought. In light of future predicted climate change, it may be increasingly important for plants of the Negev Desert to make use of dew as a water resource as it may play an important role in their ability to cope with the associated hydrological constraints predicted for the Negev region. |
| [8] | . This conclusion is supported by dew measurements al 40 cm above ground. Dew measurements at 40 cm above ground at the south-facing midslope station and at both wadi beds were significantly higher ( p < 0.05) than at 0.7 cm above ground. Facilitating an efficient radiational cooling, and beyond the impact of the surface temperatures, dew measurements at this height correspond to the classical model, highlighting the important impact of surface temperatures and ventilation upon near-ground dew condensation in an arid drainage basin. |
| [9] | . Evaluations of plant water use in ecosystems around the world reveal a shared capacity by many different species to absorb rain, dew, or fog water directly into their leaves or plant crowns. This mode of water uptake provides an important water subsidy that relieves foliar water stress. Our study provides the first comparative evaluation of foliar uptake capacity among the dominant plant taxa from the coast redwood ecosystem of California where crown-wetting events by summertime fog frequently occur during an otherwise drought-prone season. Previous research demonstrated that the dominant overstory tree species, Sequoia sempervirens , takes up fog water by both its roots (via drip from the crown to the soil) and directly through its leaf surfaces. The present study adds to these early findings and shows that 80% of the dominant species from the redwood forest exhibit this foliar uptake water acquisition strategy. The plants studied include canopy trees, understory ferns, and shrubs. Our results also show that foliar uptake provides direct hydration to leaves, increasing leaf water content by 2 11%. In addition, 60% of redwood forest species investigated demonstrate nocturnal stomatal conductance to water vapor. Such findings indicate that even species unable to absorb water directly into their foliage may still receive indirect benefits from nocturnal leaf wetting through suppressed transpiration. For these species, leaf-wetting events enhance the efficacy of nighttime re-equilibration with available soil water and therefore also increase pre-dawn leaf water potentials. |
| [10] | . Epidermal hydathodes were found on leaves of 46 of 48 species of Crassula collected from the Namib Desert in southern Africa. The possibility that these structures might allow the absorption of surface water was investigated in 27 species (including subspecies). The presence of hydathodes on leaf epidermi correlated, in most cases, with increases in leaf thickness and enhanced rates of nocturnal, and sometimes diurnal, CO_2 uptake following wetting of the leaves during the night. The precise nature of these responses varied depending on the species. In addition, wetting only the older leaves on the lower portion of the shoot of C. tetragona ssp. acutifolia not only resulted in increased thickness of these leaves, but also effected an increase in leaf thickness and stimulation of CO_2 uptake rates in the distal, younger portion of the shoot that was not wetted. Overall, foliar hydathodes were implicated in the absorption of surface water in many species of Crassula such that the ecophysiology of these desert succulents was positively affected. Although rainfall in the Namib Desert is infrequent, surface wetting of the leaves is a more common occurrence as a result of nighttime dew or fog deposition. Presumably, species with hydathodes benefit directly from this source of moisture. These findings have important implications in understanding a relatively unexplored adaptation of some xerophytes to an extremely arid environment. |
| [11] | . This study investigates the extent to which seed production in Schinus molle is dependent upon pollinators and outcrossing with the objective of understanding whether pollination and seed set could be a barrier to the spread of S. molle in arid savannas of South Africa. Pollination experiments demonstrated that seed set was greater in female flowers exposed to natural pollinators than in those from which pollinators were excluded. However, the fact that a few seeds were also found in treatments protected from pollinators and not treated with pollen may indicate that some S. molle flowers might be bisexual and capable of self-pollination. The results Suggest that S. molle fruit set is mainly affected by insect pollination, but there is also the possibility of self-pollination and apomixis. (C) 2009 Elsevier Ltd. All rights reserved. |
| [12] | . |
| [13] | . The effects of summer drought, dew deposition on leaves and autumn rainfall on plant water relations and diurnal variations of photosynthesis were measured in two evergreen shrubs, rosemary ( Rosmarinus officinalis ) and lavender ( Lavandula stoechas ), grown in Mediterranean field conditions. Withholding water for 40 d caused a similar decrease in predawn shoot water potential (ψ pd ) from c. 610.4 to c. 611.3 MPa in both species, but a 50% decrease in the relative leaf water content in L. stoechas compared with 22% in R. officinalis . A similar decrease in CO 2 assimilation rates by c. 75% was observed in water-stressed plants of both species, although L. stoechas showed smaller photosynthesis: stomatal conductance ratio than R. officinalis (35 vs 45 μmol CO 2 :mol H 2 O). The relative quantum efficiency of photosystem II photochemistry also decreased by c. 45% at midday in water- stressed plants of both species. Nevertheless, neither L. stoechas nor R. officinalis suffered drought-induced damage to photosystem II, as indicated by the maintenance of the ratio F v : F m throughout the experiment, associated with an increase in the carotenoid content per unit of chlorophyll by c. 62% and c. 30%, respectively, in water-stressed plants. Only L. stoechas absorbed dew by leaves. In this species the occurrence of 6 d of dew over a 15-d period improved relative leaf water content by c. 72% and shoot water potential by c. 0.5 MPa throughout the day in water-stressed plants, although the photosynthetic capacity was not recovered until the occurrence of autumn rainfall. The ability of leaves to absorb dew allowed L. stoechas to restore plant water status, which is especially relevant in plants exposed to prolonged drought. |
| [14] | . In order to better understand the effect associated with global climate change on Iran’s climate condition, it is important to quantify possible shifts in different climatic types in the future. To this end, monthly mean minimum and maximum temperature, and precipitation from 181 synoptic meteorological stations (average 1970–2005) have been collected from the meteorological organization of Iran. In this paper, to study spatial changes of Iran’s climatic zones affected by climate changes, Extended De Martonne’s classification (originally formulated by De Martonne and extended by Khalili ( 1992 )) was used. Climate change scenarios were simulated in two future climates (average conditions during the 2050s and the 2080s) under each of the SRES A1B and A2, for the CSIRO-MK3, HadCM3, and CGCM3 climate models. Coarse outputs of GCMs were downscaled by delta method. We produced all maps for three time periods (one for the current and two for the future) according to Extended De Martonne’s classification. Finally, for each climatic zone, changes between the current and the future were compared. As the main result, simulated changes indicate shifts to warmer and drier zones. For example, in the current, extra arid-cold ( A1.1m2 ) climate is covering the largest area of the country (21.402%), whereas in both A1B and A2 scenarios in the 2050s and the 2080s, extra arid-moderate ( A1.1m3 ) and extra arid-warm ( A1.1m4 ) will be the climate and will occupy the largest area of the country, about 21 and 3802%, respectively. This analysis suggests that the global climate change will have a profound effect on the future distribution of severe aridity in Iran. |
| [15] | . Over the last 20 years, dew harvesting has evolved to fruition because of a better understanding of its physics, thermodynamics, and the radiative cooling process of condensing substrates. Although resultant yields are relatively small, dew positions itself as a viable water resources supplement because it occurs naturally and frequently in many locations globally, particularly in the absence of precipitation or when more traditional water sources are subject to depletion. Moreover, dew water is generally potable, especially in rural locations, where it is most beneficial. This review summarizes dew harvesting research achievements to date including formation processes, collection in various environments, prediction models, water quality, and applications. The paper concludes with outlining existing gaps and future research needs to improve the understanding and performance of dew harvesting in the context of adaptation to climate change. |
| [16] | . Dew is a significant source of available water in arid and semi-arid regions, and it is considered as being the primary water source that supports living things in extreme arid regions. The objective of the present study was to determine temporal and spatial variation and the influencing factors of dew in natural sparse elm woods and grassland in Hunshandak Sandland, Inner Mongolia. One of the goals of this study was to quantify dew accumulation and duration in different types of vegetation based ecosystems. Dew formation, duration, accumulation, and environmental factors were continuously measured from the end of July to early October, 2014 during the growing season utilizing the weighing method and condensation surface technique. Leaf surfaces of the natural ecosystem were used as the condensation surfaces and served as a tool to determine the atmospheric condensation water on the plant leaves. PVC tubes with undisturbed soil were weighed before being placed into the soil at night and were reweighed before sunrise the next morning to determine dew formation in the soil from both atmospheric and deep soil layer condensation. The experiment was conducted from July 22 to October 10, 2014 and there were 4302days of dew formation during this time. Daily dew duration was averagely 4.0402h and 5.6902h in sparse elm woods and grassland, respectively, and daily dew accumulation was 0.1202mm and 0.2402mm, respectively. The total dew accumulation was 1.4402mm in sparse elm woods and 5.9502mm in the grassland ecosystem. Dew accumulation was significantly higher in grassland than in sparse elm woods ( p 02=020.029). Daily dew accumulation was the highest in July, with a value of 0.1102mm, followed by 0.10 mm and 0.0302mm in August and September, respectively, for sparse elm woods, while the highest value for grassland was 0.2602mm in July, followed by 0.2202mm, 0.1602mm, and 0.1202mm in August, September, and October. Soil dew mainly depended on the water vapor arising from the deep soil layers, rather than atmospheric water vapor. The highest values occurred in September and were 0.2902mm and 0.3502mm in sparse elm woods and grassland. Soil displayed water vapor lost to the atmosphere and the evaporation of soil was larger than the amount of condensation even at night, which was due to higher soil temperature in the upper 502cm soil layer than that of the air temperature. Soil water evaporation also provided a large amount of water vapor for atmospheric dew, and enhanced by increasing relative air humidity near the ground surface. Dew was largely affected by air temperature and relative air humidity in both sparse elm woods and grassland, followed by wind speed. Dew accumulation increased with rising relative air humidity. In conclusion, dew was a variable water source and was affected by multiple factors, not only climatic factors but also vegetation coverage. Dew accumulation and duration were lower under sparse elm wood canopies than in grassland. |
| [17] | . . 采用蒸馏水喷雾(模拟雾)法, 测定了西双版纳地区干季中10种附生植物和非附生植物叶片水势(Φ)、相对含水量(RWC)和吸水量的变化,探讨了不同类型植物叶片的吸收雾水的能力.结 果表明,随喷雾时间的延长,植物叶片Φ、RWC和吸水量均升高,说明附生植物和非附生植物叶片都能吸收雾水,但附生植物叶片吸水后Φ升高明显快于非附生植 物.附生植物附着实蕨和爬树龙叶片吸水快、RWC变化大,表明其叶片吸收雾水的能力强;贝母兰和掌唇兰叶片吸水能力低于非附生植物中的穿鞘花和野靛稞,但 高于其它4种非附生植物.傍晚雾生之前附生植物叶片Φ显著低于清晨,表明夜间附生植物叶片吸收了雾水;而非附生植物傍晚叶片Φ与清晨水势差异不显著,夜间 几乎不吸收雾水.除贝母兰外,附生植物叶生物量分数高于非附生植物,利于其吸收雾水.由于西双版纳地区干季多雾,该区植物叶片最低水势均在-0·8MPa 以上,水分胁迫不严重. |
| [18] | . |
| [19] | . . 凝结水是维系干旱、半干旱地区主要食物链的水分来源之一，具有重要的生态意义。较详细地列举了目前国内外在干旱区测定凝结量及其持续时间所采用的研究方法，从凝结水的数量特征以及时间格局两方面阐述了不同地域凝结水的时空差异性，并从气象因素、凝结面的类型及其位置、周边植被对其作用等方面综合分析了影响凝结水发生的主要因素，探讨了干旱区凝结水的生态作用及其意义，展望了干旱区凝结水未来的研究趋势。提出在未来的干旱区凝结水研究中应加强与气象学、生态学等多学科的交叉，从能量平衡角度加强对凝结水量的研究；同时，改进和规范凝结水的测量方法，开展荒漠植被对凝结水的生理响应研究以及凝结水对极端干旱胁迫植物的作用研究。 |
| [20] | . . |
| [21] | . . 通过模拟凝结水实验,研究了荒漠被毛植物雾冰藜和无毛植物沙米的叶片是否吸收凝结水。试验设计无模拟凝结水、偶尔发生凝结水以及频繁发生凝结水3个处理,每个处理又分干旱条件和人工浇水两组控制试验,研究了模拟凝结水对雾冰藜和沙米枝条相对含水量、水势、净光合速率、气孔导度、基径、地上和地下生物量的影响。结果表明,对于被毛植物雾冰藜而言,模拟凝结水显著提高了人工浇水和干旱条件下的气孔导度和地上生物量,仅提高了干旱条件下植株的水势、相对含水量、净光合速率以及地下生物量;而对于植株的基径有较小的效应。对于无毛植物沙米而言,模拟凝结水对两种水分条件下的枝条相对含水量、水势、净光合速率、气孔导度、基径、地上和地下生物量影响不大。因此,有毛植物雾冰藜的叶片可以吸收凝结水,并且其植株的光合作用、水分关系以及其生长都会对凝结水的发生产生响应,而无毛植物沙米叶片不吸收凝结水。 |
1
1995
... 本研究表明, 干旱胁迫下, 每周发生3次凝结水和每周发生5次凝结水与无凝结水处理相比, 羊草的地上生物量分别提高了9%和12%, 冰草的地上生物量分别提高了6%和14%; 羊草的根系生物量分别提高了20%和23%, 冰草的根系生物量分别提高了3%和9%, 凝结水对两种植物生物量影响的变化趋势与前人的研究结果一致(
Dew in Israel and its effect on plants
1964
Foliar uptake of fog water and transport belowground alleviates drought effects in the cloud forest tree species,Drimys brasiliensis(Winteraceae)
1
2013
... 凝结水是指大气或土壤孔隙中的水汽在地面或物体表面温度低至露点时凝结生成的液态水(
半湿润沙地凝结水的初步研究
1
1995
... 凝结水是指大气或土壤孔隙中的水汽在地面或物体表面温度低至露点时凝结生成的液态水(
Foggy days and dry nights determine crown-level water balance in a seasonal tropical montane cloud forest
1
2014
... 凝结水是指大气或土壤孔隙中的水汽在地面或物体表面温度低至露点时凝结生成的液态水(
Direct absorption of water by hairy leaves of Phlomis fruticose and its contribution to drought avoidance
1
1994
... 研究者在不同生态系统中对凝结水是否能够补充植物生长所需水分进行的研究已经证实, 地中海气候区的植物、热带雨林植物、针叶树、需水量少的地衣、苔藓以及附生植物都可以吸收叶片表面的凝结水来补充植物生长过程中对水分的需求.早期的研究发现, 凝结水的发生可以减弱甚至避免干旱胁迫下植物光合速率的下降(
The role of dew in Negev desert plants
1
2015
... 凝结水是指大气或土壤孔隙中的水汽在地面或物体表面温度低至露点时凝结生成的液态水(
Dew variability within a small arid drainage basin in the Negev Highlands, Israel
1
2000
... 凝结水是指大气或土壤孔隙中的水汽在地面或物体表面温度低至露点时凝结生成的液态水(
Foliar water uptake, a common water acquisition strategy for plants of the redwood forest
2009
Leaf epidermal hydathodes and the ecophysiological consequences of foliar water uptake in species of Crassula from the Namib Desert in southern Africa
2000
Direct foliar absorption of rainfall water and its biological significance in dryland ecosystems
1
2010
... 凝结水是指大气或土壤孔隙中的水汽在地面或物体表面温度低至露点时凝结生成的液态水(
Role of dew on the recovery of water-stressed Melissa officinalis L. plants
2
1999
... 凝结水是指大气或土壤孔隙中的水汽在地面或物体表面温度低至露点时凝结生成的液态水(
... 研究者在不同生态系统中对凝结水是否能够补充植物生长所需水分进行的研究已经证实, 地中海气候区的植物、热带雨林植物、针叶树、需水量少的地衣、苔藓以及附生植物都可以吸收叶片表面的凝结水来补充植物生长过程中对水分的需求.早期的研究发现, 凝结水的发生可以减弱甚至避免干旱胁迫下植物光合速率的下降(
Diurnal variations of photosynthesis and dew absorption by leaves in two evergreen shrubs growing in Mediterranean field conditions
1999
Spatial changes of extended De Martonne climatic zones affected by climate change in Iran
1
2013
... 凝结水是指大气或土壤孔隙中的水汽在地面或物体表面温度低至露点时凝结生成的液态水(
Dew as a sustainable non-conventional water resource: A critical review
1
2015
... 凝结水是指大气或土壤孔隙中的水汽在地面或物体表面温度低至露点时凝结生成的液态水(
Formation and influencing factors of dew in sparse elm woods and grassland in a semi-arid area
1
2017
... 试验中凝结水是在暗室中通过超声波加湿器来产生.根据野外试验结果表明, 浑善达克沙地草地凝结水通常在20:00左右发生, 到22:00左右凝结水量开始显著增加, 直到第二日6:00-7:00达到最大值(
西双版纳地区附生与非附生植物叶片对雾水的吸收
2006
Relationship between dew presence and Bassia dasyphylla plant growth
2012
干旱区凝结水研究进展
1
2008
... 凝结水是指大气或土壤孔隙中的水汽在地面或物体表面温度低至露点时凝结生成的液态水(
凝结水对温带荒漠一年生植物生态作用研究
1
2009
... 本研究表明, 干旱胁迫下, 每周发生3次凝结水和每周发生5次凝结水与无凝结水处理相比, 羊草的地上生物量分别提高了9%和12%, 冰草的地上生物量分别提高了6%和14%; 羊草的根系生物量分别提高了20%和23%, 冰草的根系生物量分别提高了3%和9%, 凝结水对两种植物生物量影响的变化趋势与前人的研究结果一致(
荒漠植物雾冰藜和沙米叶片对凝结水响应的模拟实验
1
2010
... 本研究表明, 干旱胁迫下, 每周发生3次凝结水和每周发生5次凝结水与无凝结水处理相比, 羊草的地上生物量分别提高了9%和12%, 冰草的地上生物量分别提高了6%和14%; 羊草的根系生物量分别提高了20%和23%, 冰草的根系生物量分别提高了3%和9%, 凝结水对两种植物生物量影响的变化趋势与前人的研究结果一致(
