高氮低磷沉降背景下亚热带常绿阔叶林粗木质残体的分解机制

Coarse woody debris is very important carbon and nutrient pools in forest ecosystems, where its decomposition rate is limited by low nitrogen and phosphorus availabilities. Currently, there is high nitrogen and low phosphorus depositions in the subtropical evergreen broad-leaved forest, which may exacerbate phosphorus limitation in wood decomposition. Therefore, it will affect nitrogen and phosphorus availabilities in coarse woody debris and its microbial decomposition processes. This proposal will select coarse woody debris of 8 tree species, covering four angiosperms and four gymnosperms, with different initial nitrogen and phosphorus concentration for a decomposition experiment in a subtropical evergreen broad-leaved forest. The nitrogen and phosphorus addition will be controlled in-situ during the experiment period. We will regularly investigate the changes of wood chemical properties, wood-inhabiting fungal communities, extracellular enzyme activities and decomposition rates. We will also look at the relationships between nitrogen and phosphorus availabilities and wood-inhabiting fungal communities or wood decomposition rates. Based on stoichiometric decomposition theories, we will explore the effect of phosphorus limitation on wood decomposition rates. Meanwhile, we will also compare effects of nitrogen and phosphorus additions on wood decomposition rates between angiosperms and gymnosperms. In the end, we will reveal the dynamic of nitrogen and phosphorus availabilities on coarse woody decomposition in subtropical evergreen broad-leaf forests. The results of this proposal will set a solid theoretical basis for ecosystem models to predict carbon fluxes, and supply information to farmers on how to manage subtropical forests, restore fertility in forest soils and improve forest productions.

粗木质残体是森林生态系统中重要的碳库和养分库，但是氮磷有效性低常常限制了粗木质残体的分解。现今亚热带常绿阔叶林面临高氮低磷的沉降问题，可能加剧磷对粗木质残体分解的限制，从而影响粗木质残体的氮磷有效性和微生物分解过程。本项目拟以亚热带常绿阔叶林不同初始氮磷含量的粗木质残体(4个被子和4个裸子植物)为研究对象，采用野外控制实验模拟氮磷沉降，在分解过程中定期采样监测，围绕氮磷添加对粗木质残体的养分含量、木栖真菌群落组成、胞外酶活性以及其分解速率等关键过程的影响开展研究，结合化学计量分解理论探讨磷限制对粗木质残体分解的影响机理，并对比氮磷输入对两类群树种分解的影响，揭示亚热带常绿阔叶林氮磷有效性对粗木质残体分解的影响机制。为气候变化背景下森林碳过程模拟、维持和恢复森林土壤肥力、提高森林生产力提供理论支撑。

粗木质残体是森林生态系统中重要的碳库和养分库，因此其分解对森林碳排放具有重要的影响。以亚热带森林四种被子植物和四种裸子植物的粗木质残体为研究对象，通过野外氮磷添加模拟大气氮磷沉降，分析粗木质残体分解三年期间的养分有效性、木栖真菌群落组成、分解速率和碳排放，研究氮磷添加对不同树种属性粗木质残体分解影响的微生物机制。结果表明：1）被子植物粗木质残体的氮磷养分有效性高于裸子植物的，被子植物粗木质残体的真菌多样性高于裸子植物的，被子植物以子囊菌占主导地位，而裸子植物以担子菌占主导地位，被子植物粗木质残体的分解速率和碳通量分别较裸子植物高2和3.1倍；2）相比氮限制，粗木质残体分解主要受磷限制，虽然氮磷添加对粗木质残体真菌多样性和群落组成影响显著，但氮添加对其分解速率的影响不显著，而磷添加显著增加分解速率和碳通量；3）磷添加提高被子植物粗木质残体真菌多样性和子囊菌与担子菌的比例，进而促进分解，而磷添加降低裸子植物粗木质残体真菌多样性和子囊菌与担子菌的比例，进而促进分解。这些结果最终揭示了树种属性调控氮磷添加对粗木质残体分解的影响及其微生物机制，有利于准确估算氮磷沉降背景下亚热带森林粗木质残体的碳排放量，为提高森林生态效应和服务“碳达峰碳中和”国家战略提供了科学依据。