氮沉降对土壤团聚体周转与有机碳稳定性的影响

Under the background of increasing global change, the stability of soil carbon pool is the key process for evaluating the future global change. As the main component of soil structure, the response of soil aggregates under nitrogen deposition will affect the dynamic of soil carbon pool. The mechanism of the formation, stability and slaking of aggregates on the stability of organic carbon will be an important basis for predicting the stability of soil carbon storage. Based on the Xinyang Forest Ecosystem Research Station located at climate transition zone station in Henan province, nitrogen was spread to simulated nitrogen deposition in a broad-leaved forest soil. Field investigation and experimental analysis will be used to trace the dynamic and turnover of soil aggregates, and the SOC content in aggregate fractions. The results of our project will comprehend how N deposition impacts on soil aggregate turnover, and then SOC stability. These findings could provide basic data and theoretical basis for evaluating the stability of soil carbon pool and improving biogeochemical model in small scale simulation.

在全球变化愈演愈烈的背景下，土壤碳库稳定性对评估未来全球变化趋势具有重要的指导意义。土壤团聚体作为土壤结构的主要支架，其对氮沉降的响应情况影响着土壤碳库的动态变化。团聚体的形成、稳定和裂解对有机碳稳定性的影响机理，必将是预估土壤碳库稳定性的重要基础。本项目以位于气候过渡区的河南省信阳森林生态系统定位研究站为实验平台，以阔叶落叶林土壤为研究对象，通过野外喷施氮素模拟氮沉降，结合野外调查和室内模拟实验分析土壤团聚体的动态与周转和有机碳含量，科学研究氮沉降对土壤团聚体周转的影响机制，进而评估研究区土壤有机碳的稳定性。为评估我国气候过渡区土壤碳库稳定性及其影响因素，以及小尺度生物地球化学模型提供基础数据和理论基础。

土壤团聚体和其包裹的土壤有机碳是调节土壤碳固存和土壤功能的重要因子。然而氮(N)沉降对土壤有机碳的稳定性的影响是多样的，且氮沉降和团聚体粒径对土壤有机碳稳定性的影响目前仍知之甚少。通过对六年野外氮添加试验，调查了团聚体分布、根系特征、土壤性质和多种有机碳稳定性(包括异养呼吸，δ13C， δ15N和微团聚体含量)。结果表明氮添加显著降低了土壤超大团聚体(2-8 mm)的含量，从而导致了团聚体平均重量直径(MWD)的显著降低。主要原因是细根长度密度(RLD)和根重密度(RWD)的升高。根据异养呼吸的降低和δ13C的升高说明团聚体内有机碳的稳定性在施氮之后有所增强，但mM和δ15N并无显著变化。结构方程模型结果表明细根、MWD和N可利用性对超大团聚体中碳稳定性具有显著的负作用，但对中等大团聚体内的碳稳定性无显著影响。这些结果表明氮添加增强了土壤碳稳定性受到土壤团聚体粒径的影响，主要是增加了团聚体内矿物结合碳的含量。本项研究对深入了解未来氮沉降对土壤碳库的影响具有重要科学意义。