冠层模拟氮沉降对杉木林林下植被及其生态功能的影响

Understory plants in forest ecosystem play an important role in affecting ecosystem processes and properties. However, little is known about the responses of these understory plants and their ecological function to nitrogen deposition, which hinders our comprehensive understanding for the responses of forest ecosystem and its feedbacks to nitrogen deposition. In this project, we set up experimental plots in the field site of a young Cunninghamia lanceolata plantation and separated the plants into overstory and understory functional groups. A simulated canopy nitrogen deposition experiment (the main treatments: 0 and 25 kg N ha-1yr-1) was conducted to investigate the effects of nitrogen addition on Chinese fir. Under the main treatments, four sub-treatments were applied as understrory removal, trenching with understrory plant, trenching without understory plants and control will be nested. Trenching method is used to eliminate the effects from overstory plants (Chinese fir). We will measure the growth and community composition of overstory and understory plants, diversity and community composition of soil microorganisms, litter decomposition and dynamics of soil available nutrients. The aim is to understand the ecological function without understory plants in response to nitrogen deposition. Based on the work of this project, the responses of ecosystem functions and processes to nitrogen deposition will be clarified for subtropical forests. This proposal theoretically helps predict the responses of terrestrial ecosystem and provide adaptation strategies to the increasing nitrogen deposition.

森林中林下灌草植物群落对生态系统过程与性质有重要的影响，但有关大气氮沉降增加背景下林下灌草植物的响应及其生态功能变化的研究比较缺乏，阻碍了全面理解氮沉降对森林生态系统的影响及其反馈。为此，本项目以亚热带广泛分布的杉木人工林为研究对象，把植物分为杉木功能群和灌草功能群，在实测大气氮沉降量的基础上开展模拟冠层氮沉降野外控制实验(2个主处理：0和25 kg N ha-1yr-1)。主处理下嵌套4种亚处理，即灌草去除、切根+灌草去除、切根+保留灌草、对照。在监测乔木和灌木生长及群落动态、土壤真菌/细菌多样性及土壤微生物群落结构、凋落物分解动态和土壤碳氮磷有效养分周转的基础上，从乔木-灌草-土壤微生物功能群相互联系的角度，探讨氮沉降背景下林下灌草植物缺失对生态系统功能的影响，揭示亚热带人工林生态功能和过程对氮沉降响应的潜在机制。为预测氮沉降增加背景下陆地生态系统响应及其生态功能的维持提供科学依据。

森林中林下灌草植物群落对生态系统过程与性质有重要的影响，但有关大气氮沉降增加背景下林下灌草植物的响应及其生态功能变化的研究比较缺乏，阻碍了全面理解氮沉降对森林生态系统的影响及其反馈。为此，本项目以亚热带广泛分布的杉木人工林为研究对象，把植物分为杉木功能群和灌草功能群，在实测大气氮沉降量的基础上开展模拟冠层氮沉降野外控制实验(2个主处理：0和25 kg N ha-1yr-1)。主处理下嵌套4种亚处理，即灌草去除、切根+灌草去除、切根+保留灌草、对照。在监测乔木和灌木生长及群落动态、土壤真菌/细菌多样性及土壤微生物群落结构、凋落物分解动态和土壤碳氮磷有效养分周转的基础上，从乔木-灌草-土壤微生物功能群相互联系的角度，探讨氮沉降背景下林下灌草植物缺失对生态系统功能的影响。结果表明，相对于对照处理（CK），N和UR处理明显地提高了叶片氮、磷内吸收率，而N×UR处理降低了叶片氮、磷的吸收率；各处理均促进凋落物叶的分解，分解周期减少1-2.8年；N处理减少了土壤含水量、土壤有机碳和全磷含量；UR处理促进土壤净氮矿化、净硝化和净氨化速率，氮素的淋溶作用增强；UR处理提高了土壤各类群微生物PLFAs量，N和N×UR处理在一定程度上降低了土壤总微生物PLFAs量，冗余分析表明N和UR处理可能通过土壤可利用性养分的变化而影响土壤微生物群落组成。季节效应对土壤理化性质，凋落物分解和养分矿化的影响通常表现出显著。通过本项目的开展，初步揭示了亚热带人工林生态功能和过程对氮沉降响应的潜在机制。为预测氮沉降增加背景下陆地生态系统响应及其生态功能的维持提供了一定的科学依据。