黄土高原人工刺槐林树木生长和导水功能的解耦特征-基于树木年轮学证据

Aims The decoupling of tree growth and hydraulic conduct efficiency has been widely reported recently,probably as a result of accelerated climatic warming scenarios.Most of related studies were based on the measurements of tree-ring stable isotopes,whereas there was few studies based on the information of anatomical vessel structure.Here we present the time series of growth rings and earlywood vessel parameters for the black locust(Robinia pseudoacacia)plantations in the Loess Plateau,in order to determine the temporal decoupling pattern between tree growth and hydraulic conduct functions and identify different climatic sensitivities of these two processes. Methods Site chronologies of ring width and earlywood vessel parameters(theoretical hydraulic diameter and potential hydraulic conductivity)were obtained from three sample sites across the north-south transect for the black locust plantations in the Loess Plateau.Several statistic were used to identify common patterns interannual growth variability of those chronologies,and correlation analyses were used to evaluate different climatic information embedded in tree-ring widths and earlywood vessel parameters. Important findings Ring widths of black locust trees revealed a significantly increasing trend during the lifetime,whereas hydraulic vessel parameters had an evidently decreasing trend,indicating temporal decoupling between tree growth and hydraulic conduct processes.Substantial difference in the decoupling were further confirmed by contrasting climatic sensitivities of the two processes.Tree growth of black locust trees was mostly limited by the condition of water availability,representing the strong correlations between ring widths with drought index,whereas hydraulic conduct of black locust trees was mostly limited by the thermal condition,representing the strong correlations between earlywood vessel parameters and temperature variables.Under the background of warm-dry climatic trends developed in the Loess Plateau,the limitation of drought stress on tree growth of black locust plantations will be strengthened and the situation of the decoupling of tree growth-hydraulic functions will even more acute in near future,consequently resulting in forest growth decline and tree mortality.This study will provide a scientific basis for the sustainable development of the large-scale ecological restoration projects for the black locust plantations in the Loess Plateau of China.