高寒草地沙化过程植被与土壤特征变化的生态阈值估算

Estimation of ecological thresholds in plant and soil properties during desertification in an alpine grassland

草地沙化是目前面临的重要环境问题,会对牧草生产与居民生活环境产生重要影响。目前关于草地沙化的研究主要集中在沙化过程植被特征与土壤性质的变化,选择何种敏感指标指示沙化过程以及如何量化沙化过程的生态阈值仍缺乏研究。本文利用空间代替时间的方法,在半干旱高寒草原区选择5种沙化梯度作为研究对象,系统研究沙化过程中植物、土壤及微生物特征的变化,并对沙化过程的生态阈值进行估算。结果显示,随着沙化程度的加深,群落盖度、地上和地下生物量表现出显著降低的趋势;土壤含水量呈现逐渐降低趋势,而土壤容重呈现逐渐升高趋势,极重度沙化草地的砾石比例显著高于其他沙化梯度。对土壤养分含量的分析显示,表层土壤(0~10cm)全碳、全氮含量逐渐降低,极重度沙化碳氮比显著高于其他沙化梯度。草地沙化过程中植被的生态阈值发生在轻度—中度沙化梯度,土壤和土壤微生物的生态阈值发生在中度—重度沙化梯度。从阈值估算来看,植物反应比土壤更加敏感,把植物群落特征变化作为指示草地沙化程度的指标更科学。同时,轻度到中度沙化梯度是沙化过程的关键时期,所以对沙化草地的早期防治至关重要。

Alpine grassland desertification is an important environmental problem,which have an important impact on grassland forage production and residents’living environment.The current studies on grassland desertification are mostly focused on the changes in vegetation and soil properties during desertification process,with no prior knowledge about which variables are more sensitive and can be used to indicate state transition in the desertification process,and how to quantify the ecological threshold of the desertification process.Using the method of space-for-time,five types of communities were selected to represent the different gradients of alpine grassland desertification to systematically study the changes in plants,soil properties,and microorganisms during the desertification process,and to identify the desertification thresholds.The results showed that plant community cover,above-ground,and underground biomass significantly decreased with the increase in desertification.Soil moisture concentration gradually decreased,and soil bulk density gradually increased with the increase in the extent of desertification.Gravel content was significantly higher in severely desertified grassland community than in other desertified community types.Soil total carbon and nitrogen concentrations in the soil surface(0-10 cm)gradually decreased,and the ratio of carbon to nitrogen was significantly higher in severely desertified community than in other types of grassland community.Abrupt changes in vegetation occurred in lightly to moderately desertified communities.Meanwhile,rapid changes in soil properties and soil microorganisms(desertification threshold)occurred in moderately to severely desertified communities.Such results suggest that the response of plants to desertification could be more sensitive than that of soil sub-systems,and plants could be treated as a more direct indicators of the gradients of grassland desertification.Moreover,mildly to moderately desertified communities could be the key stage of grassland desertification.Thus,it is very important to take the right methods to avoid further desertification of the grassland.