根系去除改变了毛竹林土壤酶活性对氮磷添加的响应

亚热带是我国氮和磷沉降的热点地区，森林生态系统碳（C）、氮（N）、磷（P）循环对N和P沉降的响应受到广泛关注。根系作为森林土壤碳和养分持续供给的重要来源，其输入变化在N和P沉降下通过影响土壤酶活性进而调控土壤碳和养分循环过程。以毛竹林为研究对象，选择硝酸铵和磷酸二氢钠分别进行N和P添加，共设置4个处理：对照、N添加、P添加和N+P添加，并结合壕沟处理，探究毛竹林土壤C、N、P循环相关酶活性对氮磷添加和根系去除的响应，并分析它们与土壤和细根化学性质之间的关系。结果表明：土壤C、N循环相关酶活性整体上对根系去除的响应比氮磷添加更敏感，这主要是因为根系去除显著降低土壤全氮和铵态氮含量，但短期氮磷添加并未显著改变调控土壤酶活性分异的土壤有机碳、全氮和铵态氮含量。与C、N循环相关酶活性不同，土壤P循环相关酶对根系去除和磷添加处理均呈现负响应，这可能是因为阻断根系P吸收和补充土壤P元素降低了微生物的P开采作用。但研究区土壤微生物仍受到P限制作用，这是因为在P缺乏毛竹林生态系统，根系比微生物具有更强的P吸收利用能力。研究结果强调了不同功能土壤酶活性对土壤养分添加和根系输入变化响应的敏感性差异，为预测低P毛竹林生态系统土壤C和养分循环提供依据。

Root exclusion changed the response of soil enzyme activity to the nitrogen and phosphorus addition in Phyllostachys edulis forest

As the hot spot of nitrogen (N) and phosphorus (P) deposition in the subtropical of China, the response of forest ecosystem carbon (C), N and P cycle to N and P deposition has got more and more concerns. As an important source of supplying of soil C and nutrients in forests, root input variations regulated the process of soil C and nutrient cycle by affecting soil enzyme activity under N and P deposition. Ammonium nitrate and sodium dihydrogen phosphate were added in moso bamboo forest as N and P addition to simulate N and P deposition in our study, respectively, and a total of four treatments were set up:control, N addition, P addition, and N+P co-addition. Combined with root exclusion treatment, the effects of root exclusion and N and P addition on soil C, N and P related enzyme activities were explored, and their relationships between soil C, N and P related enzyme activities and soil and fine root chemical properties were analyzed for further. The results showed that the response of soil C and N related enzyme activities to root exclusion was more sensitive than those to N and P addition in general, which caused from the negative response of soil total nitrogen and ammonium nitrogen to root exclusion, but the neutral response of soil organic carbon, total nitrogen and ammonium nitrogen to short-term N and P addition. Different from the activities of C and N related soil enzyme to root exclusion and N and P addition, soil P related enzyme activities showed a negative response to root exclusion and phosphorus addition, respectively, which may be attributed to decline in microbial P mining effect. Because preventing of root P absorption caused from root input variations in trench plots and supplementing of soil P under P addition and N+P co-addition treatments may reduce the utilization of soil P by microorganisms in our study site. Despite all this, soil microorganisms are still suffering from P limitation under P addition treatment in our study area, and the main reason is that the underground root system has stronger P absorption and utilization capacity than microorganisms in the P-deficient moso forest ecosystem. Our results highlight the discrepancy of the responses of multiple functional soil enzyme activities to soil nutrients addition and root input variations, and provide a basis for predicting soil C and nutrient cycling in low-P moso bamboo forest ecosystem.