Abstract：
Recent droughts have strongly impacted forest ecosystems and are projected to increase in frequency, intensity, and duration in the future together with continued warming. While evidence suggests that tree diversity can regulate drought impacts in natural forests, few studies examine whether mixed tree plantations are more resistant to the impacts of severe droughts. Using natural variations in leaf carbon (C) and nitrogen (N) isotopic ratios, that is δ13C and δ15N, as proxies for drought response, we analyzed the effects of tree species richness on the functional responses of tree plantations to the pan-European 2018 summer drought in seven European tree diversity experiments. We found that leaf δ13C decreased with increasing tree species richness, indicating less drought stress. This effect was not related to drought intensity, nor desiccation tolerance of the tree species. Leaf δ15N increased with drought intensity, indicating a shift toward more open N cycling as water availability diminishes. Additionally, drought intensity was observed to alter the influence of tree species richness on leaf δ15N from weakly negative under low drought intensity to weakly positive under high drought intensity. Overall, our findings suggest that dual leaf isotope analysis helps understand the interaction between drought, nutrients, and species richness.
摘要：
最近的干旱严重影响了森林生态系统，预计频率会增加，强度,和未来的持续时间以及持续的变暖。虽然有证据表明树木多样性可以调节天然森林的干旱影响，很少有研究检查混合树木种植园是否对严重干旱的影响更具抵抗力。利用叶碳（C）和氮（N）同位素比的自然变化，也就是δ13C和δ15N,作为干旱响应的代理，在七个欧洲树木多样性实验中，我们分析了树木物种丰富度对树木种植园对泛欧洲2018年夏季干旱的功能响应的影响。我们发现叶片δ13C随着树种丰富度的增加而降低，表明干旱胁迫较少。这种影响与干旱强度无关，也不是树种的干燥耐受性。叶片δ15N随干旱强度增加，表明随着水的供应减少，向更开放的N循环转变。此外,观察到干旱强度将树种丰富度对叶片δ15N的影响从低干旱强度下弱负改变为高干旱强度下弱正。总的来说,我们的发现表明，双叶同位素分析有助于理解干旱之间的相互作用，营养素,物种丰富。
