天童栲树冠层叶片碳同位素组成特征及与光合参数关系

Characteristics of the Leaf Carbon Isotope in the Castanopsis fargesii Canopy and Their Relationship to Photosynthetic Parameters in the Tiantong Mountain

植物冠层叶片存在稳定性碳同位素贫化效应,反映了冠层光合能力的异质性。通过测试不同月份栲树冠层冠顶至冠下8m叶片δ^(13) C及叶片最大光合速率(A_(max))和单位质量叶片氮含量(N_(mass)),分析了冠层叶片δ^(13) C的时空分布特征及其与A_(max)和N_(mass)的相关关系,验证树高极限的水力限制假说。结果表明:不同月份和冠层高度对冠层叶片δ^(13) C存在极为显著的影响(p<0.01),从冠顶到冠下8m叶片δ^(13) C平均值的变化范围为-28.61‰^-31.67‰,冠层叶片δ^(13) C随冠层高度降低呈线性极为显著减小(R^2=0.727,p<0.001);冠层叶片δ^(13) C随A_(max)和N_(mass)的增大而增大,呈极为显著的对数曲线关系(R^2=0.514,R^2=0.610,p<0.000 1),不支持树高极限的水力限制假说。

Leaf carbon isotopic depletion exists in plant canopy,which indicates the photosynthetic heterogeneity of canopy.In order to study the temporal and spatial changes of leafδ-（13） C along canopy vertical gradient,and test whether the hypothesis of tree height limit from hydraulic limitation is true in the Castanopsis fargesii,the values of leafδ-（13）C,maximum assimilation rate（A_（max））,and leaf nitrogen content per unit mass（N_（mass））were measured from crown to 8mcrown below in different months.The results showed that the different months and canopy heights significantly affected on canopy leafδ-（13） C（p0.01）.The mean value of leafδ-（13）C ranged from-28.61‰to-31.67‰ along canopy vertical gradients from crown to 8mcrown below,and significantly linearly decreased with the decrease of canopy heights（R-2=0.727,p0.001）.Canopy leafδ-（13）C significantly increased with the increase of A_（max）and N_（mass）（p0.000 1）,and their relationship followed the logarithmic curve very well（R-2=0.514 for A_（max）,and R-2=0.610 for N_（mass））,which proved that the hypothesis of tree height limit from hydraulic limitation seems to be unlikely in the Castanopsis fargesii.