气温升高与氮沉降增加联合作用对高寒草地碳循环关键过程的影响机制研究

In this study, two types of open-top chambers (OTCs) with the height of 0.4m(T1) and 0.8m(T2), and different concentrations of NH4NO3 aqueous solution, are utilized to simulate global warming and nitrogen deposition. On this basis, an orthogonal experiment with two factors and three levels is designed in the alpine grassland ecosystem on the Qinghai-Tibetan Plateau. Two typical alpine grassland ecosystem, alpine meadow and swamp meadow, are selected as the research objects. Through the long-term observation (3 to 5 years), the community structure and biomass dynamics of alpine grassland are studied, on this basis, response characteristics and its internal mechanism of the community structure and net primary productivity (NPP) to elevated temperatures, increased nitrogen deposition, and their combined action are revealed. . Meanwhile, the soil samples in different depth ( 0-10cm, 10-20cm, 20-30cm) are collected and analyzed, including total organic content, microbial biomass carbon, and dissolved organic carbon. Furthermore, the effects of the elevated temperatures, increased nitrogen deposition, and their combined action on the soil organic carbon content, fractions, and profile distribution of alpine grassland ecosystem could be clearly grasped.. In addition, the seasonal and daily variations of CO2 emission fluxes are obtained by the observation of the ecosystem respiration and soil respiration under different manipulations. On this basis, the response characteristics of the CO2 emission fluxes to elevated temperatures, increased nitrogen deposition, and their interaction could be analyzed. At the same time, the regulation factors of CO2 emission fluxes could be realized.. Finally, under the background of global climate change, the interrelations and interaction between the key processes of carbon cycle which were represented by biomass dynamics and net primary productivity (NPP), soil organic carbon content and fractions, and CO2 emission fluxes, are analyzed synthetically.

采用高度分别为0.4m和0.8m的开顶式增温小室，并以不同浓度NH4NO3水溶液为外加氮源，对青藏高原高寒草地生态系统进行模拟增温和氮沉降增加的两因素三水平正交实验。通过长期定位观测（3-5年），了解两种典型高寒草地群落结构特征和生物量季节动态，明确生物量动态及净初级生产力（NPP）对增温、氮沉降增加以及二者联合作用的响应特征和内在机制；采集不同深度土壤样本进行分析，指标包括总有机碳、微生物量碳、水溶性有机碳，掌握高寒草地土壤有机碳含量、组分和分布状况，分别对两种气候要素变化及其交互作用的响应规律；在不同处理内进行全年生态系统呼吸与土壤呼吸速率观测，确定CO2排放通量的日变化和季节变化特征，及其对增温、氮沉降增加及其交互作用的响应特征，掌握其内在调控因素；最终综合分析气候变化条件下，以生物量与净初级生产力、土壤有机碳含量和组分、CO2排放通量为代表的碳循环关键过程之间的彼此联系与相互作用。

本研究探讨了气候变化条件下青藏高原高寒草地生态系统CO2排放、群落生物量生产、土壤有机碳组分的动态特征和调控机制，并试图阐明各碳循环过程间的内在联系。结果表明短期增温、施氮及其交互作用对高寒草地生态系统呼吸均有较显著的促进作用，气温和土壤温度两因素可共同解释不同处理内大部分生态系统呼吸的变异。植被群落生物量积累和分配方式的变化也是决定生态系统呼吸变异的重要因素，短期增温使地上及地下生物量均显著增加，但地下生物量分配比例呈上升趋势；短期施氮仅对地上生物量产生明显的促进作用，表明氮输入导致植物将更多的生物量分配至地上部分；增温与施氮交互作用显著的促进地上及地下生物量的积累，但对生物量的分配格局并未产生显著的影响。而土壤有机碳含量随增温幅度提高明显下降，原因与增温加速表层有机质分解、促进微生物代谢有关；相反，施氮则通过刺激植物生长尤其是地上生物量的积累，从而促进生态系统碳蓄积，最终导致土壤有机碳含量的增加；增温同时施氮显著提高了土壤有机碳含量，且两因素交互方式表现为明显的协同作用，这可能源于施氮使得地上生物量显著增加，导致土壤水分、温度对增温的响应不敏感，因此施氮对有机碳的促进作用被突显。