生物土壤结皮对毛乌素沙地油蒿群落土壤水分的影响

为进一步探究毛乌素沙地油蒿群落内结皮对土壤水分的影响，研究了结皮(地衣结皮和苔藓结皮)未受干扰和移除处理下的土壤水分入渗、蒸发及含水量状况。结果显示:1)两种结皮均对土壤水分入渗具有抑制作用，移除两种结皮后，土壤水分初渗速率、稳渗速率以及累积入渗量均显著增大(P < 0.05)；2)结皮对土壤蒸发的影响与结皮类型及蒸发阶段有关，地衣结皮对整个蒸发过程中日蒸发量及蒸发总量无显著影响(P>0.05)，而苔藓结皮对土壤日蒸发量的影响在模拟蒸发前期表现为抑制(第1~5天)，后期表现为促进(第6~15天)，但对总蒸发量的影响不显著(P>0.05)；3)总体来看，地衣结皮覆盖区0~40cm土层含水量高于地衣结皮移除区，而苔藓样地规律则相反。从不同土层来看，相比于移除结皮，地衣结皮覆盖区40cm深度以上各层土壤含水量均较高，苔藓结皮覆盖区土壤含水量在5和10cm深度较高，20和40cm较低。研究结果表明，地衣结皮提高了油蒿群落土壤水分有效性，应对其进行保护；苔藓结皮降低了油蒿种群土壤水分有效性，却提高了浅根系草本土壤水分有效性，这是驱动油蒿群落演替的重要因素之一。研究在为毛乌素沙地油蒿群落提供水分管理依据的同时，也从土壤水分方面为该群落的演替提供一定解释。 

Influence of biological soil crusts on soil moisture in Artemisia ordosica community in Mu Us Desert,northwestern China

Biological soil crusts ( BSCs ) are widely distributed in Artemisia ordosica community in Mu Us Desert, northwestern China. They have been proved to play vital hydrological and ecological roles in desert ecosystems. However, the influence of BSCs on soil hydrological processes remains uncertain and controversial. In this study, we conducted a field experiment with two treatments ( undisturbed and removed) for two biological soil crusts ( lichen crusts and moss crusts) in A. ordosica community in the Mu Us Desert. We compared soil infiltration, evaporation and soil water volume in crust-covered and crust-removed soil. The initial infiltration rate, stable infiltration rate and cumulative infiltration significantly increased under crust-removed treatment ( P<0. 05 ) , suggesting that lichen and moss crusts had inhibitory effects on soil water infiltration. The effect of BSCs on soil evaporation was related to the type of BSCs and the evaporation stage. The lichen crusts had no effect on daily soil evaporation and total soil evaporation(P>0. 05). The influence of moss crusts on total soil evaporation was similar to that of lichen crusts. The moss crusts inhibited daily soil evaporation in early soil evaporation stage ( 1--5th day), and promoted it in the late stage (6--15th day). Generally, the soil moisture above 40 cm depth under crust-covered soil was higher than that in crust-removed soil, but opposite in moss soil. The soil moisture at each layer above 40 cm depth in crust-covered soil was higher than that in crust-removed soil. Compared with the crust-removed soil, soil moisture in crust soil was higher at 5 and 10 cm, but lower at 20 and 40 cm. The results indicated that lichen crusts should be reserved with no disturbance. Whether the moss crusts should be reserved or disturbed need further discussion. Our results highlight the different hydrological roles of lichen and moss crusts and provide important implications for the management of soil water resource in semiarid areas of northwestern China.