草毡表层演化对高寒草甸水源涵养功能的影响

Mattic Epipedon Impact on Water Conservation in Alpine Meadow

高寒草甸占青藏高原面积的60%,是高原水源涵养功能发挥的主体基质。近几十年来高寒草甸呈现多模式、多途径、重危害的退化特征,已对我国水资源安全造成威胁。因此,在青海省果洛州和海北州,以典型高寒矮嵩草(Kobresia humilis)草甸为研究对象,采取时空互代的方法,对其草毡表层厚度对土壤持水功能的影响进行研究,并分析影响水源涵养功能发挥的土壤因子,明晰人类活动干扰对高寒草甸水源涵养功能的作用。结果表明:随着高寒矮嵩草草甸由禾草-嵩草群落向矮嵩草群落、小嵩草(Kobresia pygmaea)群落和杂类草-"黑土型"次生裸地的演替,其土壤饱和持水量和田间持水量均呈单峰变化曲线,最高值出现于小嵩草群落时期(草毡表层开裂期),分别为117.08%和105.75%,最低值出现于杂类草-"黑土型"退化草地时期,分别为70.00%和60.92%;在自然条件下,草地自然含水量表现出随退化演替持续降低的趋势,土壤持水能力和草地自然含水量呈现出不同的行为分异特征。土壤容重、孔隙度、活根/土体积比、草毡表层厚度和地表生物结皮发育程度均是影响高寒矮嵩草草甸土壤持水能力发挥的主要因子,持水量与土壤孔隙度和活根/土体积比成正比,与土壤容重成反比,土壤中牧草活根对水分的吸附是高寒矮嵩草草甸水源涵养的主要机制。土壤降水入渗速率与土壤持水量无关,但却与草地自然含水量成显著相关关系。草毡表层的加厚,有利于土壤持水能力的提高,但伴随着生物结皮扩张与老化,会导致降水入渗速率的降低。保持适度厚度的草毡表层是保障高寒矮嵩草草甸水源涵养生态功能发挥的关键。

Alpine meadow covering about 60% of the area in the Tibetan plateau is a main component for water conservation.Alpine meadow presents the degraded features of multi-pattern,multi-gateway,serious danger during recent decades,while safety of water resource in our country has been challenged.Alpine Kobresia humilis meadow was selected as the research target in this study.The degraded succession of alpine meadows was divided into four stages： Graminoids ＋ Kobresia humilis community,Kobresia humilis community,Kobresia pygmaea community and forb-＂black soil type＂ grassland.The coupling process and mechanism between the capacity of water conservation and Mattic epipedon（M.E.） of alpine meadow were investigated to understand the influence of soil factors on water conservation using spatial-time metathesis research methods.Result indicted that the change of soil saturation and field moisture capacity appeared a single peak curve.The maximum was in K.pygmaea stage and was 117.08% and 105.75%,respectively.However,the minimum was in forb-＂black soil type＂ grassland stage and was 70.00% and 60.92%,respectively.Soil bulk density,soil porosity,volume ration of live root and soil mineral substance（R.M.）,M.E.and biological crust（B.C） had influence on soil water conservation.Soil water conservation had a significant positive correlation with soil porosity or the volume ration of R.E.,whereas it had a negative correlation with soil bulk density.The adsorption of live root to moisture was an important mechanism of soil moisture entreasure in alpine meadows.Thickening of M.E.was helpful to increase water conservation.The extreme development of B.C.prevented water infiltration.A suitable depth of M.E.（about 4.3 cm） is the suggested optimal stage for water conservation of alpine meadow.