穿透雨减少和氮添加对毛竹叶片和细根化学计量学的影响

全球气候变化导致的干旱和人类活动引起的大气氮沉降升高，将会直接影响森林生态系统的结构与功能。叶片和细根作为植物最重要的资源获取功能器官，其化学计量学特征可指示其资源利用、生存适应策略。在当前气候变化背景下，了解植物的化学计量特征和适应特征将有助于预测未来森林生态系统功能的变化。通过为期1年的双因素交互实验，探讨了穿透雨减少和氮添加影响下，我国亚热带重要森林类型毛竹林的叶片及细根碳（C）、氮（N）、磷（P）元素化学计量比的响应特征，对于认识毛竹林生态系统对全球变化的适应和养分利用策略具有重要意义。研究表明：（1）穿透雨减少处理显著降低叶片N、P含量，显著增加细根N含量，对叶片C含量和细根C、P含量无显著影响；氮添加处理显著增加土壤N含量和叶片N含量，对叶片C、P含量及细根C、N、P含量无显著影响。（2）穿透雨减少、氮添加处理及两者交互作用对土壤C：N：P均无显著影响。（3）穿透雨减少处理显著增加叶片C：N、C：P和N：P；氮添加处理显著降低叶片C：N，对叶片C：P、N：P无显著影响；穿透雨减少、氮添加交互作用显著降低叶片C：N和C：P，对叶片N：P无显著影响。（4）穿透雨减少处理显著降低细根C：N，对细根C：P及N：P无显著影响；氮添加处理及穿透雨减少、氮添加交互作用对细根C：N：P无影响。综上短期处理的研究结果，穿透雨减少处理产生的水分胁迫对毛竹产生了关键限制作用，毛竹采取了降低叶片N和P含量、增加细根N含量，提高叶片的N和P利用效率、保持细根稳定的P利用效率的策略。氮添加未能缓解穿透雨减少对毛竹产生的干旱胁迫，毛竹通过改变地上部分叶片和地下部分细根之间的N素分配格局和N、P利用效率以应对水分胁迫。氮添加处理下叶片N含量显著增加，C：N显著降低，而细根C、N、P含量及化学计量比没有显著变化。由此可知毛竹地上部分叶片和地下部分细根对穿透雨减少、氮添加及两者交互作用表现出不同的响应策略。本研究可为全球变化背景下毛竹人工林可持续经营提供理论依据。

Effects of throughfall reduction and nitrogen addition on stoichiometry of leaf and fine root in Phyllostachys edulis forests

The drought caused by global climate change and the increased atmospheric nitrogen deposition caused by human activities will directly affect the structure and function of forest ecosystems. Leaves and fine roots are the most important resource-obtaining functional organs of plants, whose stoichiometry characteristics can indicate their resource utilization and survival adaptation strategies. Under the background of climate change, understanding the stoichiometry and adaptive characteristics of plants will be beneficial to predict future changes in the forest''s ecosystem functions. Through a two-factor interaction experiment for one year, this study explored the response characteristics of the stoichiometry ratio of carbon (C), nitrogen (N), and phosphorus (P) elements in leaves and fine roots of Moso bamboo (Phyllostachys edulis) forest (an important subtropical forest type in China) under the dual influences of throughfall reduction and nitrogen addition. It is of great significance for understanding the adaptation of Moso bamboo forest ecosystem to global changes and nutrient utilization strategies. The results showed that (1) the throughfall reduction significantly decreased N and P contents in leaves, but significantly increased N content in fine roots, and had no significant effect on C content in leaves as well as C and P contents in fine roots. Nitrogen addition significantly increased N content of soil and N content in leaves, but had no significant effect on C, P contents in leaves and C, N, P contents in fine roots. (2) The throughfall reduction, nitrogen addition and their interaction had no significant effect on the ratio of C:N:P of soil. (3) The throughfall reduction significantly increased the ratios of C:N, C:P, and N:P in leaves. Nitrogen addition significantly decreased the ratio of C:N in leaves, but had no significant effect on the ratios of C:P and N:P in leaves. The interaction of throughfall reduction and nitrogen addition significantly decreased the ratios of C:N and C:P in leaves, but had no significant effect on the ratio of N:P in leaves. (4) The throughfall reduction significantly decreased the ratio of C:N in fine roots, but had no significant effect on the ratios of C:P and N:P in fine roots. Nitrogen addition and the interaction of throughfall reduction and nitrogen addition had no effect on the ratio of C:N:P in fine roots. Our study indicated that Moso bamboo adopted strategies to reduce N and P contents in leaves, increase N content in fine roots, improve N and P utilization efficiency in leaves, and maintain fine roots'' stable P utilization efficiency. Nitrogen addition failed to alleviate drought stress caused by the throughfall reduction on Moso bamboo. Moso bamboo coped with drought stress through changed N distribution pattern and N, P utilization efficiency between the aboveground (leaves) and the underground (fine roots). Under the treatment of nitrogen addition, N content in leaves increased significantly, and the ratio of C:N decreased significantly. However, C, N, and P contents in fine roots as well as the stoichiometric ratio did not change significantly. It can be seen that the aboveground (leaves) and the underground (fine roots) of Moso bamboo have different response strategies to the throughfall reduction, nitrogen addition and their interaction. This study can provide theoretical basis for the sustainable management of Moso bamboo plantation under the background of global change.