模拟氮沉降条件下森林凋落叶释放单萜烯对土壤微生物和酶活性的影响

Nitrogen deposition increased continuously in recent years, which will influence the decomposition of litter, the soil microbial community structure and function. The decomposition of litter is the major source of monoterpenes and other volatile organic compounds in the soil, which has great impacts on soil ecological processes. The increasing of nitrogen deposition can influence the emission of monoterpenes from the decomposition of litter, and then they will influence the soil microbial communities and the soil enzymatic activities, which will finally change the cycles of soil carbon and nitrogen. In this project, three permanent nitrogen deposition fields located in Dinghushan Biosphere Reserve (DBR) in the low-subtropics will be selected. The impacts of the increasing nitrogen deposition on the emission of monoterpenes from the litter and soil will be studied in different forests in field, and their impacts on the soil microbial communities and the soil enzymatic activities will be measured synchronously. In the laboratory experiments, soil and different major individual litter in DBR will be selected, and the species and emission rates of monoterpenes from them will be monitored along the decomposition of litter under different levels of simulated nitrogen deposition. The change of soil microbial communities and soil enzymatic activities with the emission of monoterpenes will be measured at the same time. With the exogenous addition of monoterpenes in the soil, the change of soil microbial communities and soil enzymatic activities will be clarified at different species and concentration of monoterpenes. With the comparison of the field and the laboratory experiments, the objective of this project is to find out the impacts of simulated nitrogen deposition on the fluxes of monoterpenes from litter and soil, and then their impacts on soil microorganisms and enzyme. The influence of the increasing nitrogen deposition and the change of monoterpenes on the soil microbial communities and the soil enzymatic activities will also be distinguished in this project. The results from this project will be of significance to deeply understand the material cycles in forest ecosystems under global change.

近年来氮沉降持续增加，影响凋落物分解、土壤微生物群落结构和功能。凋落物分解是土壤单萜烯等挥发性有机化合物的重要来源，对土壤生态过程有重要影响。氮沉降增加可影响凋落物释放单萜烯，从而影响土壤微生物群落和土壤酶活性，并改变土壤碳氮循环。本项目选取南亚热带鼎湖山氮沉降样地为研究对象，野外测量氮沉降增加对不同森林凋落物和土壤单萜烯释放的影响，及其对土壤微生物群落和酶活性的影响。室内模拟不同氮沉降水平，分析鼎湖山土壤和主要树种凋落叶单萜烯释放随凋落叶分解的变化过程，以及土壤微生物群落和土壤酶活性随单萜烯释放的变化。向土壤中添加外源单萜烯，进一步阐明不同单萜烯种类和浓度对土壤微生物和酶活性的影响。通过野外和室内模拟对比，得到氮沉降增加条件下凋落物单萜烯释放对土壤微生物和酶的影响，并区分氮沉降增加和单萜烯改变对土壤微生物群落和酶活性的影响。结果对深入了解全球变化条件下森林生态系统物质循环有重要理论意义。

氮沉降影响凋落物分解、土壤微生物群落结构和功能，而凋落物分解是土壤单萜烯等BVOCs重要来源，氮沉降可通过影响凋落物释放单萜烯进而影响土壤微生物群落和土壤酶活性，进一步改变生态系统物质循环。本项目首选野外选取鼎湖山自然林为研究对象，分析了土壤和凋落叶单萜烯通量，进而以其长期氮沉降样地为研究对象，分析了森林地表单萜烯通量对氮沉降的响应；其次温室模拟不同氮沉降方式和沉降量对马尾松和荷木盆栽幼苗植物和土壤VOCs通量及土壤微生物的影响，在此基础上分析氮水交互对土柱栽培木荷、海南红豆、马尾松和杉木植物和土壤BVOCs的影响及其机理；最后室内运用自制TGCS系统，分析了氮添加对木荷、马尾松和杉木凋落叶分解过程中单萜烯等BVOCs释放的影响及其对土壤微生物和酶的影响，进而通过土壤添加实验，从机理上探讨了土壤微生物和酶与单萜烯吸收和释放的关系。结果表明，（1）氮沉降对不同森林地表BVOCs通量影响差异较大，氮沉降降低马尾松林地表部分BVOCs吸收或地表由汇变为源，抑制阔叶林地表部分BVOCs释放或使地表由源变为汇；（2）土壤施氮促进马尾松BVOCs释放但叶面施氮无显著效果，而两种施氮方式均导致木荷BVOCs释放量下降，且土壤表层施氮对土壤微生物量、群落结构和土壤细菌影响较大。施氮显著影响杉木异戊二烯释放，木荷、海南红豆和马尾松植物单萜烯和异戊二烯释放不同季节差异显著。（3）凋落叶分解释放BVOCs集中在前期，马尾松凋落叶释放烯烃量最大，氮添加促进了凋落叶单萜烯等BVOCs的释放，但外源氮导致除放线菌外的其他土壤微生物生物量降低，而促进纤维素酶和酚氧化酶活性而抑制了β-葡糖苷酶、脲酶、天冬酰胺酶、蛋白酶和酸性磷酸酶活性；（4）不同单萜烯对土壤微生物群落结构影响差异不一，暂未发现降解单萜烯的特异性微生物，但单萜烯对β-葡糖苷酶有显著抑制作用。研究结果对深入了解全球变化背景下森林物质循环有重要理论意义。项目发表论文16篇，18人次参加国际和国内会议，指导博士后1名，培养研究生10名。