黄土高原藓类生物结皮对表层土壤水分运动参数的影响

Effects of moss-dominated biocrusts on surface soil-water movement parameters in the Chinese Loess Plateau

生物结皮普遍存在于干旱和半干旱地区土壤表层,对土壤水分有重要影响。为了进一步探究生物结皮对表层土壤水力学特性和水分运动过程的影响,该研究以黄土高原风沙土和黄绵土上发育的藓结皮为研究对象,通过野外采样与室内试验相结合,测定了藓结皮覆盖土壤和无结皮土壤的Boltzmann变换参数、土壤水分扩散率、入渗过程、比水容量和非饱和导水率,对比分析了有无藓结皮覆盖对表层土壤水分运动参数的影响。结果表明:藓结皮覆盖抑制了表层土壤水分的扩散,藓结皮覆盖土壤的Boltzmann变换参数和水分扩散率分别比无结皮土壤降低7.9%~27.3%和99.2%~99.6%;藓结皮覆盖后表层土壤渗透性显著降低,其水分入渗参数(初始入渗率、稳定入渗率、平均入渗率、累积入渗量)和非饱和导水率分别降低了17.1%~55.4%和84.8%~92.3%;藓结皮显著提升了表层土壤的持水和供水能力,藓结皮层的水分常数(田间持水量、萎蔫系数、重力水含量、有效水含量和易利用水含量)比无结皮土壤高40.9%~1233.3%,土壤水吸力在100 kPa时的比水容量比无结皮土壤高7.4%~1540.5%;相比黄绵土,藓结皮覆盖对风沙土的渗透性影响较小,而对土壤持水和供水性的影响较大。综上,黄土高原藓结皮覆盖降低了土壤渗透性,同时显著提高了表层土壤的水分有效性,这可能导致土壤表层在雨后截留较多水分,进而使土壤水分分布趋于浅层化,并改变该地区的土壤水分有效性和植物水分利用策略。

Biological soil crusts(biocrusts)are the common living skin of the land face in arid and semiarid regions.They greatly change the hydropedological features and soil-water movement of surface soil.But the influencing mechanism is still lacking,especially on water infiltration and retention.Taking the Loess Plateau of China as a study area,this study aims to explore the effects of moss-dominated biocrusts on the fundamental parameters in the surface soil-water movement,with emphasis on the characteristics of water infiltration and water retention.The moss biocrusts(naturally developed for>30 years)and uncrusted soil formed on the aeolian sandy and loess soil were firstly collected in the Liudaogou watershed in the northern Loess Plateau.Afterwards,four treatments were carried out to measure the parameters of Boltzmann transformation,soil water diffusivity,infiltration,specific water capacity,and unsaturated hydraulic conductivity on-site or in the laboratory after sampling.A comparison was finally made on the soil-water movement parameters between the biocrusts and uncrusted soil.The results showed that the biocrust layer impeded the horizontal movement of surface soil water both in the aeolian sandy and loess soil.Specifically,the Boltzmann transformation parameter and soil water diffusivity of biocrusts decreased compared with the uncrusted soil.Moreover,the biocrusts highly decreased the water infiltrability of surface soil,subsequently the whole soil profile.The initial,stable,and average infiltration rates of biocrusts,the cumulative infiltration amount and unsaturated water conductivity of biocrusts decreased compared with the uncrusted soil.Additionally,the mean values of soil water parameters(including saturated water content,field capacity,wilting point,gravitational water content,available water content,and readily available water content)and specific water capacity at soil suction of 100 kPa of biocrusts were 40.9%–1233.3%and 7.4%–1540.5%higher than that of the uncrusted soil,respectively,implying that the biocrusts greatly improved the soil water holding capacity and availability.Most importantly,the low infiltrability and high water holding capacity of moss biocrusts were closely related to the contents of sand and silt,as well as the organic matter in the biocrust layer.The biocrusts that developed on the aeolian sandy soil presented weaker effects on the soil infiltrability,but stronger effects on the water retention and availability,compared with the biocrusts on the loess soil.The reason was that there was a 1–2 cm thick layer with particular properties(e.g.,soil texture,organic matter content,and bulk density)in the moss biocrusts.Therefore,the availability of soil water increased greatly,whereas,the diffusivity and infiltrability decreased significantly in this case.Consequently,the biocrusts can possibly make the upper soil(such as 0–50 cm)retain more water,while inhibiting the water infiltration into the deep soils after rainfall.Subsequently,the availability of soil water can be altered for the water use strategy of vegetation in fragile arid and semiarid ecosystems of the Loess Plateau.