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草地是陆地生态系统的重要组成部分,具有重要的生产和生态功能[1]。世界草地面积约占全球陆地面积的40%[2],它不仅是畜牧业重要的生产基地,且在调节气候、保持水土、改良土壤和维持生物多样性等方面发挥着巨大作用[1-3]。我国天然草地面积约在349×104392×104 km2,约占国土总面积的40%以上[1, 4]。近半个世纪以来,受全球气候变化及人类活动影响,我国草地面临水资源短缺、植被退化、生态功能和生产力持续下降等严峻的生态问题[3]。
水分是干旱半干旱地区植被生长和生态恢复的主要限制因子。目前,全世界80%的草地位于干旱半干旱地区,该地区具有降水稀少、蒸发量大、水资源储量低等特点[5]。降水格局变化首先对土壤水分分布有影响[2],进而影响草地植物个体和生态系统水分利用效率[6],最终影响草地生态系统水循环过程及生产力水平[7]。
前人对草地生态系统水文过程的研究,主要集中于运用传统水文学方法研究其水文过程的某一环节,如植被层对降水的截留和分配[8-9]、植被蒸散[10]、土壤水分蒸发[11]及土壤水分入渗[12]等方面,且缺乏将草地生态系统各水体作为一个整体进行综合研究并定量化;而稳定同位素技术具有较高的灵敏度与准确性,可将生态系统水循环过程(包括从大气降水到地表水、土壤水、地下水、植物水和蒸发水等整个迁移、转化与分配过程)作为一个整体来研究,系统和定量地阐明其过程与机制[13-14]。
本文综述了碳氢氧稳定同位素在草地生态系统水循环研究中的国内外进展,并展望其未来的应用前景,对我国草地资源保护、科学利用以及退化草地生态系统恢复等具有重要的指导意义。
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