树木叶片稳定碳同位素分馏对环境梯度的响应

Changes in leaf stable carbon isotope fractionation of trees across climatic gradients

除了自身的遗传因素外,植物对稳定碳同位素的分馏还受温度、水分状况、光照等多种环境因素的影响。通过对生长在中国北热带、亚热带和温带的13个气候区树木的稳定碳同位素分馏与环境要素的关系的研究得出,不同气候条件下树木叶片稳定碳同位素比率(δ13C)和稳定碳同位素分辨率(Δ)差异明显,分别在-23.759‰--33.914‰和14.581‰-24.354‰的范围内。且由南向北,δ13C值呈现逐渐加重的趋势、而Δ值逐渐减小。年均温度、相对湿度、降雨量及无霜期等与δ13C值呈显著负相关、与Δ值显著正相关;年均日照时数、气温年较差、蒸发量、纬度及海拔等与δ13C值呈显著正相关、而与Δ值显著负相关;而经度、年极端最高气温等与δ13C和Δ值的相关性较弱。δ13C和Δ值的变化幅度和趋势在年均温度、年较差、无霜期、活动积温分别达到约19℃、23℃、309d、6000℃出现转折,这些指标在此基础上继续增加反而使叶片δ13C值增大、Δ值减小。而当年均降雨量和相对湿度分别超过1105mm、75%以及蒸发量小于约1700mm后,δ13C和Δ值随之变化的幅度也变小。结果表明在亚热带和温带的分界线以南,水热条件均能满足植物正常生理活动的需要,环境条件的相对改变对植物生理活动及叶片稳定碳同位素分馏的影响较小;而在北方,干旱、低温等极端的外界环境条件加剧了对植物生长和生理指标的影响、造成了不同环境梯度下叶片稳定碳同位素分馏的差异。

Stable carbon isotope discrimination occurs in photosynthetic carbon assimilation process. Stable carbon isotope fractionation （Δ） in plants is determined by genetic characteristics and photosynthetic styles,while also greatly influenced by many environmental elements such as temperature,water status,irradiance condition,and atmospheric CO2 concentration. The relationship between leaf stable carbon isotope ratio （δ^13C） and temperature or rainfall continues to be a controversial and unresolved problem in the field of plant eco-physiology. In this study,we determined the correlations of leaf δ^13C and Δ of tree species with environmental factors across different climate gradients in China using Mass Spectrometry Methods and statistical analysis. The one-way ANOVA results showed that there was a significant difference in the leaf δ^13C and Δ values between the different climate zones. Both leaf δ^13C and Δ value had strong correlations with the most climatic and other environmental factors. In each sample place,annual average temperature,including annual lowest temperature and annual highest temperature,annual relative humidity,annual rainfall and annual frostless periods were all significantly negatively correlated with leaf δ^13C values,whereas,the climatic factors were significantly positively correlated with leaf Δ values. δ^13C values had significantly positive relationships with annual sunshine hours,annual sunshine percentage,annual temperature range,annual evaporation,altitude and elevation,whereas Δ value had significantly negative relationships with annual sunshine hours,annual sunshine percentage,annual temperature range,annual evaporation,altitude and elevation. Change trend of leaf δ^13C and Δ values in each site did not significantly vary until annual temperature,temperature range,annual frostless periods and annual ≥10℃ accumulated temperature respectively reached to 19℃,23℃,309d,6000℃,and then the Leaf δ^13C values increased and Δ values decreased with the increase of the above temperature indices. When annual rainfall,annual relative humidity and annual evaporation were more than 1105mm,75% and less than 1700mm,changes in leaf δ^13C and Δ values at different places were slowing down with the changing of water status. The influences of topographic factors such as latitude,longitude,elevation on leaf Δ values are indirect,as the topographic factors are mainly correlated with the climatic factors including water,temperature and irradiance conditions,and they together affect leaf Δ values. There was no significant relationship between leaf δ^13C and Δ values with longitude,or annual extreme maximum temperature. The above results suggested that the water and caloric requirement of plants was basically satisfied in sub-tropical and tropical area,therefore relatively environmental change in these areas had to a less degree influence on tree physiological behaviors and leaf stable carbon isotope fractionation. However,in northern part,the exterior environmental factors,such as lower moisture and lower temperature,all significantly limited plant growth and physiological performance,and these extreme climatic factors caused the variation in leaf carbon isotope fractionation in the 13 sampling places across different climatic gradients.