亚热带次生林外生与丛枝菌根树种对土壤氮循环的影响及其作用机制

土壤氮循环对森林生态系统结构、功能及其对全球变化的响应都具有重要的影响。菌根能帮助植物获取氮素从而调节土壤氮循环过程，但不同类型菌根树种影响土壤氮循环的特征及作用机制尚不明确。本项目以亚热带典型次生林为研究对象，以丛枝菌根（AM）与外生菌根（EcM）树种对土壤氮循环的影响为切入点，（1）通过野外菌根调查构建AM和EcM树种优势及梯度变化样地，研究不同菌根类型树种丰度变化对土壤氮循环的影响及规律；（2）通过凋落物原位分解及土壤氮矿化试验，并结合凋落物质量、酶动力学、氮转化功能基因丰度及微生物多样性，阐明“菌根树种-土壤-自由微生物”相互作用驱动凋落物分解及土壤氮转化的机制；（3）通过随机区组-15N同位素示踪试验，并结合根际酶谱及分泌物特征，揭示不同菌根类型树种的“根际效应”对不同形态氮吸收的影响。研究结果可为森林土壤氮循环预测、模型发展及评估全球变化背景下森林结构与功能的响应提供科学依据。

Soil nitrogen (N) cycling has an important influence on structure and function of forest ecosystem and its response to global changes. Mycorrhizas can enhance plant nitrogen acquisition and thus affect the soil N cycling. However, the effects of mycorrhizal tree species on soil N cycling and the underlying mechanisms are remaining unclear. Hence, this proposal was designed to investigate the effects of arbuscular (AM) and ectomycorrhizal (EcM) tree species on soil N cycling in subtropical forests. This will be approached by combination of field and laboratory experiment. The main content of this research includes: (1) Plots with mycorrhizal trees gradients will be established in field to investigate the effects of relative abundance of AM and EcM tree species on soil N cycling. (2) The experiments of litter decomposition and soil N mineralization, together with the analysis of litter quality, enzyme kinetics, nitrogen functional gene abundance and microbial community diversities, will be conducted to clarify the mechanisms of “mycorrhizal trees-soil-micrograms” driving the litter decomposition and nitrogen transformation. (3) the experiment of random blocks design-15N isotope labeling, together with the analysis of zymogram and secretion in rhizosphere, will be conducted to reveal the “rhizosphere effects” of mycorrhizal trees quantitative on uptake of N forms. Findings from the project will helpful in the prediction of soil nitrogen cycling, the development of models and the assessment of the responses of structure and function of forest ecosystem to global changes.