高寒草甸草地退化对土壤水热性质的影响及其环境效应

Alpine Meadow Degradation Effect on Soil Thermal and Hydraulic Properties and Its Environmental Impacts

青藏高原高寒草甸草地的大面积退化,将改变浅层土壤的水热性质,影响地表水热交换,甚至导致区域生态环境的变化。本文通过系统分析典型原生高寒草甸与中度退化高寒草甸的植物群落特征、地上地下生物量和土壤理化特征的差异,研究高寒草甸草地退化对土壤水热性质的影响及其环境效应。结果表明:随着高寒草甸草地退化,植被覆盖度显著降低(p<0.01),适应旱生、深根系的杂草侵入适应湿润生境、浅根系的以莎草科植物为主的原生植被,生物多样性显著增加(p<0.01);草毡表层(0~10cm)地下生物量显著减少(p<0.01),30~50cm地下生物量显著增加(p<0.01)。草毡表层变薄降低了土壤容重的垂向异质性,使表层土壤容重显著增加(p<0.01),土壤颗粒显著变粗(p<0.01)。受浅层土壤有机质降低和土壤容重增加的影响,中度退化高寒草甸土壤的持水量和饱和导水率降低,土壤导热率升高。高寒草甸草地植被退化,土壤持水量、饱和导水率降低和导热率增加将加速地表水热交换,对高寒草甸草地退化和下伏多年冻土消融都可能是正反馈。

Widely distributed degradation of alpine meadow in the Qinghai-Tibet Plateau changes water retention capacity,hydraulic conductivity,and thermal conductivity in the shallow soil layer,which could affect surface water and heat fluxes and feedback to regional ecological environment.We compared plant community characteristics,above and underground biomass,and soil physical and chemical properties between typical native and moderately degraded alpine meadow to understand the effect of land degradation on soil thermal and hydraulic properties and environment.The results showed that vegetation coverage reduced significantly(p<0.01)in moderately degraded alpine meadow.Forbs with deep roots replaced the native sedges which have shallow roots to ensure the ecosystem acclimate the drier environment.Under moderate degradation,biodiversity of alpine meadow ecosystem significantly increased(p<0.01).Underground biomass in mattic epipedon(0-10 cm)significantly decreased(p<0.01),however,it significantly increased(p<0.01)in 30-50 cm soil layer.Mattic epipedon thinning decreased vertical heterogeneity in soil bulk density,and bulk density of surface soil significantly increased(p<0.01).The soil tended to coarsen with degradation(p<0.01).Surface soil water retention capacity and saturated hydraulic conductivity decreased,and soil thermal conductivity increased in moderately degraded alpine meadow because surface soil organic matter significantly decreased and soil bulk density increased.The results of this research suggest that the grassland degradation in alpine meadow results in decreases in soil water retention capacity and increases in soil thermal conductivity,which could accelerate land surface water and heat exchange.In addition,the decrease in vegetation coverage and mattic epipedon could lead to a potential positive feedback to permafrost thawing and regional climate warming.