基于同位素示踪的高寒草甸碳氮分配格局对草毡表层加厚的响应

Overgrazing made the mattic epipedon thicken of alpine meadow, then dehisced and denuded, these phenomenons were the typical alpine meadow degeneration, According to some statistics, this appeard aboat 60 percent on alpine meadow. The study of “relation between mattic epipedon thickening and stability of the grass ”have not got proper attention, caused degradation mechanism and process of uncertainty. The study of carbon and nitrogen cycle in the mattic epipedon thickening process is the key to understanding the mechanism of mattic epipedon thickening. Stable isotope technique can make up for the long-term field experiment in the time scale, inaccuracy. In this study two periods of degraded alpine meadow meadow types are set as the research object. Using the 13C、15N stable isotope technique to make certain How C and N distribution and fixation in the ecosystem units, and response to mattic epipedon thickening. model the mattic epipedon thickening time with redundancy analysis(Borcard, 2011) and strengthen the regression tree (Elith, 2008). We study from the perspective of the geochemical cycle to clear the machanism of mattic epipedon thickening process and mechanism.This study will not only contribute to advance the the carbon and nitrogen cycle theory, but also benefit to grassland management and renovation.

超载放牧下，高寒草甸草毡表层的加厚、开裂、剥蚀是其退化的代表性特征，据统计有60%的高寒草甸出现草毡表层剥蚀。草毡表层发育与草地稳定性丧失的关联这一科学问题没有得到足够重视，造成高寒草甸退化过程与机制不确定性。草毡表层加厚过程中C、N积累的研究是理解草毡表层加厚机理的关键，稳定同位素技术能弥补长期田间实验在时间尺度、精确性上的不足，本研究以正常小嵩草草甸和小嵩草加厚期草甸为研究对象，利用13C、15N同位素示踪技术，分析C、N在高寒草甸生态系统关键构件（植被、凋落层、植物根系、土壤）中的分配、流通对于草毡表层加厚的响应，并通过冗余分析(Borcard, 2011)和增强回归树(Elith, 2008)构建草毡表层形成时间与根系生物量、植被盖度、土壤养分、降水、年均温间模型。本研究从地球化学循环角度明晰高寒草甸草毡表层加厚引起草地稳定性丧失的发生过程和机理，为完善草地C、N循环提供理论支持。

本研究在位于青海省祁连山地区的中国科学院海北高寒草甸生态系统定位站进行，以不同退化程度高寒草甸为研究对象，利用样方调查、土壤养分分析结合同位素示踪技术，主要开展了草地退化过程植被特征演替、草地退化过程水热条件差异分析实验、草毡表层加厚与草地生产力、干旱处理下高寒草地固态能力研究，以及通过这些实验进行了影响草地退化关键因子分析，研究了不同退化程度高寒草地生态系统植被生境调查分析，揭示了高寒草地退化演替过程中植被生物量、盖度、功能群变化、土壤物理性状、养分特征、水热条件和固碳能力变化情况，发现了草毡表层过度发育严重影响草地生产力、储水能力和碳氮固定能力的现象，比较了不同植物类群对于放牧压力和干旱胁迫的反应，提出了莎草科植物更具放牧和干旱忍耐性的理论，为高寒草地的适应性管理提供科学理论支撑。