疏勒河上游高寒草地斑块对生态系统碳交换及估算的影响研究

The landscape pattern with different patches mosaic coexisting is common in the alpine grassland on the Qinghai-Tibetan Plateau (QTP). Satellite remote sensing is usually used to estimate ecosystem carbon pool and flux at large scale. However, it is difficult to distinguish patches commonly existed in the alpine grassland on the QTP, which would influence the accuracy of remote sensing retrieval. This project proposes to investigate the effects of patches on ecosystem carbon exchange and estimation of alpine grassland based on the field observation at pixel scale of satellite remote sensing in Shule river basin. Ecosystem carbon stock, ecosystem carbon flux, abiotic and biotic factors of different patches will be observed in field to illuminate the response of ecosystem carbon exchange to patches. The effect of patches on the estimation of ecosystem carbon stock and flux will be analyzed quantitatively in conjunction with field observation data of ecosystem carbon stock and flux and satellite remote sensing index. This project is conducive to reducing the uncertainty of remote sensing retrieval and supplying base data for ecological, hydrological models. Meanwhile, this research is also important for alpine grassland protecting and the restoration of degraded grassland.

不同斑块镶嵌共存的景观格局在青藏高原高寒草地普遍存在。在大尺度上通常采用卫星遥感反演系统碳储量和通量，但其精度不足以分辨青藏高原高寒草地上普遍存在的斑块，因而影响反演的精度。本项目拟在卫星遥感像元尺度采用实地观测对疏勒河上游高寒草地斑块对生态系统碳交换及估算的影响进行研究。通过观测不同斑块生态系统碳储量和通量以及生物和环境因子的特征，阐明高寒草地生态系统碳交换对斑块的响应机制；同时基于不同斑块生态系统碳储量和通量的观测结果，结合卫星遥感指数，分析斑块导致的估算结果的不确定性。本项目的开展可以为生态、水文模拟提供基础资料，减少遥感反演的不确定性；同时为高寒草地生态系统保护和退化草地生态恢复提供科学依据。

本项目综合利用遥感反演、无人机航拍和野外观测等手段，开展了斑块破碎化对高寒草地生态系统碳碳储量和通量变化及估算结果的影响研究。研究结果表明：1）基于遥感反演，无人机航拍和样地调查的方法研究发现斑块破碎化加剧了高寒草地系统碳的空间异质性，不考虑这种空间异质性会引起对高寒草地生态系统碳储量和排放的高估；2）由于植被盖度的降低和地下根系的减少，斑块破碎化导致高寒草地生态系统蒸散发加强和土壤水分向深层下渗，不利于裸地斑块植被的生长和恢复；3）斑块破碎化和高原鼠兔的挖掘活动减少了呼吸底物供应和土壤含水量，从而导致高寒草地碳排放减少，但是生态系统呼吸作用的减弱无法抵消光合作用碳固定效应。本项目可以为生态、水文模式研究提供基础资料，同时为多年冻土区高寒草地生态系统保护和退化草地生态恢复提供科学依据。但同时目前关于斑块形成的驱动力还不明确，尤其是高原鼠兔在高寒草地斑块形成和发展过程中的作用。从而给高原鼠兔管理和退化草地恢复措施的实施带来了很大的不确定性。因此，在将来的研究中需要开展长期定点工作予以明确。