Functionally dissimilar neighbors improve tree water use efficiency through increases in leaf phosphorus concentration

Water use efficiency (WUE) is central to the global cycles of water and carbon. However, whether increasing tree diversity in plantation can increase WUE remain poorly understood. Here, we conduct a forest biodiversity experiment with 32 tree species spread in 14 ha in subtropical China to assess the effects of neighboring tree diversity on foliar WUE of Cunninghamia lanceolata, a widespread tree plantation species in China. We measure foliar δ13C as the proxies of changes in intrinsic WUE. Folia P concentrations of focal trees increase with trait dissimilarities between focal trees and neighbors, and the increased foliar P concentrations improve foliar WUE of focal trees. This neighborhood complementarity effect on WUE is stronger under more shaded neighborhood. However, neighborhood biodiversity did not significantly affect foliar δ18O, a surrogate for stomatal conductance. These findings suggest that tree biodiversity increases WUE through the complementary usages of soil P between neighboring tree species.

水分利用效率（Water Use Efficiency, WUE）是全球水、碳循环的核心环节。然而，人工林内提升树木多样性是否能够提高水分利用效率，目前仍缺乏足够的研究认知。本研究在中国亚热带地区14公顷的实验样地中开展森林生物多样性实验，共纳入32个树种，旨在探究邻体树木多样性对中国广泛种植的人工林优势树种杉木（Cunninghamia lanceolata）叶片水分利用效率的影响。我们以叶片δ¹³C作为内在水分利用效率变化的替代表征指标。研究发现，目标树的叶片磷浓度随其与邻体树木的功能性状差异增大而升高，而叶片磷浓度的提升可显著改善目标树的叶片水分利用效率。这种邻体互补效应对水分利用效率的增益作用，在邻体遮阴程度更高的生境中更为突出。不过，邻体树木多样性并未对叶片δ¹⁸O——气孔导度的替代指标——产生显著影响。上述研究结果表明，树木多样性可通过邻体树种间对土壤磷资源的互补利用，提升整体水分利用效率。