Data from: Convergence in resource use efficiency across trees with differing hydraulic strategies in response to ecosystem precipitation manipulation

1. Plants are expected to respond to drought by maximizing the efficiency of the most limiting resource, the water use efficiency (WUE), at the expense of nitrogen and carbon use efficiencies (NUE and CUE). Therefore, plants resource use efficiencies are viewed as indicators of species drought tolerance. 2. We tested these predictions by measuring leaf-level intrinsic WUE (WUEi, the ratio of net assimilation to stomatal conductance), photosynthetic NUE (PNUE, the ratio of daily maximum net assimilation to leaf nitrogen content) and leaf-scale CUE (approached by the ratio of nighttime respiration to daytime net assimilation, Rd/An) in piñon pine and juniper, two tree species that differ in drought tolerance and vulnerability to drought-induced mortality. Variations in resource use efficiency in the two species were measured in response to seasonal drought and in response to an ecosystem-scale precipitation manipulation experiment comprising three precipitation treatments: ambient, irrigation (+30%) and partial rainfall exclusion (-45%). 3. Increasing water limitation, either seasonally or across treatments, resulted in increased WUE and decreased PNUE and CUE in both species. WUE, PNUE and CUE varied more strongly in response to water limitation than across species and converged to the same relationships against precipitation for piñon and juniper. 4. Plasticity in WUE, PNUE and CUE in response to water limitation was associated, in both species, with low carbon acquisition during drought. Our results exhibited a convergence in resource use efficiency across piñon and juniper which contradicts the paradigm that resource use efficiencies are indicators of species drought tolerance and ecological strategy.1. 植物应对干旱的策略通常为最大化最限制性资源的利用效率——水分利用效率（water use efficiency, WUE），同时以牺牲氮素利用效率（nitrogen use efficiency, NUE）与碳利用效率（carbon use efficiency, CUE）为代价。因此，植物的资源利用效率被视为物种耐旱性的指示指标。2. 本研究以耐旱性与干旱诱导死亡易感性存在显著差异的两种乔木——皮诺松（piñon pine）与杜松（juniper）为研究对象，通过测定叶片水平的内在水分利用效率（intrinsic WUE, WUEi，即净同化速率与气孔导度的比值）、光合氮素利用效率（photosynthetic NUE, PNUE，即日最大净同化速率与叶片氮含量的比值）以及叶片尺度碳利用效率（以夜间呼吸速率与日间净同化速率的比值Rd/An表征），对上述预测进行了验证。同时，本研究还测定了两种植物的资源利用效率对季节性干旱的响应变化，并结合一项包含三种降水处理的生态系统尺度降水调控实验开展分析：三种处理分别为自然对照、灌溉（增雨30%）与部分减雨（减雨45%）。3. 无论是季节性干旱还是不同降水处理下的水分限制加剧，均导致两种植物的WUE升高，同时PNUE与CUE降低。相较于物种间的固有差异，三种资源利用效率对水分限制的响应幅度更为显著，且皮诺松与杜松的资源利用效率随降水量变化的关系趋于一致。4. 两种植物的WUE、PNUE与CUE对水分限制的表型可塑性，均与其在干旱期间的碳获取能力降低显著相关。本研究结果显示，皮诺松与杜松的资源利用效率存在趋同现象，这与“资源利用效率可作为物种耐旱性与生态策略的指示指标”这一经典研究范式相悖。