植物群落中C3和C4植物的比例和组成对诸多生态系统过程具有重要影响.解析C3和C4植物碳同位素的环境驱动过程与调控因子,对于从土壤碳同位素的角度来预测C3/C4植被比和组成具有重要意义.本研究旨在评估草原植物碳同位素特征的种内变异将如何影响C3和C4植物的碳同位素组成以及C3/C4植被比的预测.沿中国北方草原的自然干旱梯度选择26个植物群落,通过分析植物和土壤的碳同位素组成,采用混合模型来预测C4植物对土壤有机碳的相对贡献.本研究对比分析了如下3种情境:(1)考虑C3和C4植物碳同位素的种内和种间效应;(2)仅考虑碳同位素的种间变异;(3)忽略碳同位素的种内和种间变异.研究结果表明,植物碳同位素组成沿中国北方草原自然干旱梯度的变化具有物种特异性.C3和C4植物的碳同位素组成与干旱指数之间呈显著负相关关系,但C3植物比C4植物对环境的干旱变化更为敏感.植物碳同位素特征的种内变异在驱动C3植物功能群碳同位素沿干旱梯度的分布格局中发挥着重要作用.如果忽略植物碳同位素特征的种内变异将会显著高估C4植物的相对贡献.本研究结果表明,草原植物碳同位素特征的种内变异对于准确预测C3/C4植被组成具有重要意义.“,”Aims Understanding the patterns and drivers of carbon isotope discrimination(13Δ)in C3 and C4 functional groups is critical for predicting C3/C4 vegetation ratio from the isotopic composition of soil organic matter.In this study,we aimed to evaluate how intraspecific variation will modify functional group-level 13Δ values and the associated prediction of C3/C4 vegetation ratio.Methods We investigated 13Δ of 726 individual plants(96 species;C3 and C4 functional groups)and topsoil organic matter in 26 grassland communities along an aridity gradient in northern China.The fraction of C4 contribution was calculated with mixing models that considered:(i)both intra-and interspecific effects on the 13Δ values of C3 and C4 functional groups;(ii)only interspecific effects;or(iii)none of these effects.Important Findings We found divergent responses of plant 13Δ at the intraspecific level to the changes of aridity across the gradient.The 13Δ of both C3 and C4 functional groups was negatively correlated with an aridity index,with higher sensitivity for C3 than for C4 functional groups.Intraspecific 13Δ variation played a key role in driving the total 13Δ variations of C3 plants.Overlooking such intraspecific effect in mixing models led to a greatly increased fraction of C4 contribution to soil organic carbon.A correction for the effects of intraspecific variation is therefore essential for correctly inferring C3/C4 vegetation ratio in the past.Our findings provide basic information for the reconstruction of past vegetation change from bulk materials in arid and semiarid biomes.