高寒草甸土壤呼吸对模拟氮沉降的响应

As a result of human activities, the amount of nitrogen compounds in the atmosphere has been increased more and more globally over the past century, which has developed into one of the main nitrogen source in ecosystem. Alpine meadow ecosystem has developed in extremely high altitude and cold environment, which is extremely vulnerable and lack in quick-acting nitrogen. It responds to nitrogen addition sensitively. As the key link in carbon cycle in terrestrial ecosystem, so it is necessary to explore the responses of soil respiration to nitrogen deposition. In this study, nitrogen addition experiment will be conducted in Kobresia humilis alpine meadow in Maqu county, Gansu province, which is in the east of Qinghai-Tibetan Plateau. Ammonium nitrate (NH4NO3) will be added at four rates: control (0 kg N/(haoa)), low nitrogen (10 kg N/(haoa)), medium nitrogen (20 kg N/(haoa)), and high nitrogen (40 kg N/(haoa)). Each plot has an area of 9 m2(3m×3m) and a 3m isolation band is set between adjacent plots. Each nitrogen treatment has four plots. In both warm season (soil temperature is above zero when is growing season from May to October) and cold season (soil temperature is below zero from November to the next April)，soil respiration diurnal change will be measured monthly using the LI-8100 Automated Soil CO2 Flux System from 2013 to 2015. The soil respiration will be separated to microbial respiration and root respiration according to root biomass extrapolation method. Parallel to the flux measurements, soil temperature and moisture at 5 cm depth will be measured. We will estimate the contribution of microbial respiration and root respiration to soil respiration for each nitrogen treatment. The proportion of warm season and cold season soil respiration to all year round will be estimated, and its responses to nitrogen deposition will be explored. Additionally, related soil characteristics, such as soil microbial biomass carbon and nitrogen, ammonium and nitrate contents, organic matter, total nitrogen and pH value will be analyzed monthly during growing season (May to October). In the meantime, the related characteristics of vegetation, such as height, coverage, diversity, aboveground and belowground biomass will be investigated. Responses of above soil and vegetation characteristics to nitrogen deposition will be explored. Finally, relations among soil respiration and its components, related soil and vegetation characteristics, and meteorological factors will be analyzed to determine the key factors driving soil respiration, microbial respiration and root respiration, and to reveal response mechanisms of soil respiration and its components to nitrogen deposition in alpine meadow. This study can offer theoretical basis and data base for soil carbon dynamic in alpine meadow ecosystem, which will help to forecasting the responses and acclimations of carbon and nitrogen cycle to nitrogen deposition.

大气氮沉降日益增加，已成为生态系统氮素的主要来源之一。高寒极端环境下所形成的高寒草甸生态系统极其脆弱，土壤速效氮贫乏，对不断增加的氮素响应敏感。土壤呼吸作为生态系统碳循环的主要环节，研究其对氮沉降的响应有重要意义。本项目以玛曲矮嵩草草甸为研究对象，通过野外控制试验模拟氮沉降（对照、低氮、中氮和高氮），对其土壤呼吸进行动态监测，采用根生物量外推法将土壤呼吸分为根系呼吸和微生物呼吸两个组分，揭示土壤呼吸及其组分的日变化和季节变化对氮沉降的响应；并同步测定相关的土壤特征（微生物量和理化性质）与植被特征（高度、盖度、多样性和生产力），阐明其季节变化对氮沉降的响应；结合气象因子，分析不同氮沉降水平下土壤呼吸及其组分同相关土壤和植被特征的关系，明确土壤呼吸及其组分的主要驱动因子，揭示高寒草甸土壤呼吸对氮沉降的响应机制，以期为预测在大气氮沉降持续增加情况下高寒草甸土壤碳动态的响应与适应提供理论依据。

大气氮沉降日益增加，已成为生态系统氮素的主要来源之一。高寒极端环境下所形成的高寒草甸生态系统极其脆弱，土壤速效氮贫乏，对不断增加的氮素响应敏感。土壤呼吸作为生态系统碳循环的主要环节，研究其对氮沉降的响应有重要意义。利用LI6400XT观测了青藏高原东缘高寒草甸生态系统的土壤呼吸及其组分对模拟氮沉降（对照、低氮、中氮和高氮）的响应。结果表明，指数模型能够较好的描述土壤呼吸月动态与温度之间的关系，高寒草甸土壤呼吸对温度的响应Q10值为3.896，高寒草甸土壤呼吸对温度响应敏感；高寒草甸生态系统的土壤微生物呼吸对土壤呼吸的贡献为70.3-80.0%；氮沉降对土壤呼吸有微弱的促进作用，但是氮沉降对微生物呼吸表现出抑制作用，对根呼吸有促进作用，而且随着氮沉降处理时间的延长，根呼吸对土壤呼吸的贡献逐渐增强。高氮添加处理对高寒草甸表层0-10cm土壤可溶性碳和亚表层10-20cm土壤微生物量碳有明显的促进作用。