中国北方农牧交错带C3草本植物δ^(13)C与温度的关系及其对水分利用效率的指示

Relationship between temperature and δ^(13)C values of C3 herbaceous plants and its implications of WUE in farming-pastoral zone in North China

由于植物稳定碳同位素组成(δ13C)综合反映了植物光合过程中C、H2O交换的信息,因而从理论上讲它可以作为植物长期水分利用效率的潜在指标,并揭示与植物生理生态过程相联系的一系列气候环境信息。通过对中国北方农牧交错带400 mm等降水样带上28个科的118种C3草本植物叶片δ13C值的测定,探讨了C3草本植物δ13C和水分利用效率(WUE)对环境温度梯度变化的响应以及气候环境因素对其产生的影响,揭示了样带控制植物δ13C变化的主要环境因子。结果显示:在400 mm降水带上C3植物δ13C分布区间为-31.5‰--23.0‰,平均值为-27.6‰,分布范围与黄土区干旱-半干旱区C3草本植物一致。整体C3植物δ13C随年均温度和夏季均温升高分别变重0.14‰/℃和0.27‰/℃,指示植物WUE随大气温度升高而增加。但这仅是一种表象,温度与植物碳同位素的这种关系实质上是温度升高导致的土壤相对湿度(或湿润指数)降低造成水分胁迫进而影响植物碳同位素分馏的结果,植物可利用的有效水分是本样带植物碳同位素分馏的控制因子。5种C3广适性植物δ13C均随温度升高而变重,但变化幅度不同,而且它们之间平均δ13C值有显著差异,表明不同物种的水分利用状况对温度的响应不同,说明不同物种有不同适应环境变化的策略。此外,本结果还显示不同寿命的草本植物δ13C值以及用碳同位素表征的WUE表现出多年生草本>2年生草本>1年生草本(可能与不同寿命草本植物的根系分布和吸水能力有关),这与Ehleringer等在沙漠地区研究的结果一致,而与湿润气候区的结果相反,表明不同寿命的草本植物δ13C值和WUE的变化可能与当地水分条件有关。

Plant carbon isotope composition（δ13C） comprehensively reflects the information of C and H2O exchange in the process of plant photosynthesis,thus,in theory it could serve as a potential indicator of long-term water use efficiency（WUE） of plants.In addition,it could also be used to reveal a series of climatic and environmental information related to plant physiology and ecology.In this paper,through the systematical measurements of δ13C values of samples representing 28 families and 118 C3 herb species along the isohyet of 400 mm in farming-pastoral zone in northern China,the responses of δ13C values and WUE for C3 plants to temperature gradients were analyzed.This study shows that,along the isohyet of 400 mm,the δ13C values of C3 plant species in farming-pastoral zone range between-31.5 ‰ and-23.0 ‰,with an average value of-27.7‰.The distribution range of plant δ13C values in this study is consistent with that of C3 plants grown in arid and semi-arid area on the Loess Plateau obtained by previous study.Statistical analyses for the whole C3 plants show that the δ13C values of C3 plants and the mean annual temperature were significantly and positively correlated with an increase in δ13C of about 0.14 ‰ per 1.0℃ increase,and that the δ13C values of C3 plants also significantly and positively relate to the summer temperature,with a increasing rate of 0.27‰ per 1.0℃ increase.The results indicate that plant WUE increases with rising air temperature.However,the phenomenon above is only a false appearance,the variations in δ13C values of C3 herbaceous plants with temperature are actually controlled by the water stress induced by the lower soil relative humidity（or humidity index） which is closely related to temperature increment.The available water for plant species growing in this belt transect is a controlling factor of plant carbon isotope fractionation.In addition,this study shows that the δ13C values of 5 C3 eurytopic plants also increase with increasing temperature,but both the slope variations and the average δ13C values among species are significantly different,which suggests that different species have different strategies to adapt to environmental changes.Also,this study shows that,for different life-span herbaceous plant,δ13C values and WUE denoted by carbon isotope ratio present the following patterns： the δ13C of biennial herbs is smaller than that of perennial herbs,and larger than that of annual herbs（This could be associated with the root distribution and water absorption ability of different life-span herbs）,and the finding is consistent with the results reported by Ehleringer in desert regimes,while opposite to the results from humid climate zone.This indicates that the δ13C values and WUE of different life-span herbs are likely related to local moisture condition.