毛乌素沙地生物结皮对水分入渗和再分配的影响

Effects of Biological Soil Crust on Water Infiltration and Redistribution in the Mu Us Sandland,Inner Mongolia,Northern China

生物结皮的发育影响着干旱半干旱区小尺度土壤水文过程。对两种自然降雨条件下(降雨量为8.5 mm和14.8 mm)的3种放牧管理类型(持续放牧地、围栏5 a禁牧区、围栏15 a禁牧区)有、无生物结皮土壤的降雨入渗速率和再分配规律进行了测定。结果如下:(1)入渗速率禁牧5 a和禁牧15 a样地的有结皮土壤的入渗速率极显著低于无生物结皮土壤。持续放牧样地上,生物结皮发育很差,其对土壤的入渗速率无显著影响。(2)入渗深度自然降雨为8.5mm的次日在持续放牧区能入渗到15～20 cm,而在禁牧5 a和禁牧15 a围栏区仅能入渗到10～15 cm。自然降雨为14.8 mm的次日在持续放牧区能入渗到30～40 cm,在禁牧5 a和禁牧15 a围栏区能入渗到20～25 cm。在无雨条件下,禁牧15 a围栏区50 cm以下土壤水分状况较禁牧5 a和持续放牧区更差。测定结果表明:生物结皮的形成降低了水分的入渗速率和自然降雨的下渗深度,使下渗水分减少,渗透深度变浅,由此可见当地高频率(84.6%)的小降雨(<10mm)事件只能对浅根系的草本有效,这将使得草本植物生长旺盛而深根系半灌木油蒿生长不良,逐渐衰退。

In arid and semiarid environments,microbiotic soil crust on the soil surface plays the major role in ecosystem processes,particularly in soil water flows,and therefore,is very important for landscape structure and function.In this paper,we examined three grazing treatments such as continuous year-long livestock grazing（grazing）,grazing excluded for 5 years（5-yr exclosure） and grazing excluded for 15 years（15-yr exclosure）,the effects of soil crust on water infiltration and redistribution were analyzed.The water infiltration rate for both in 5-yr and 15-yr exclosures is as follows：bare areasoil with microbiotic crust,which showed that the presence of microbiotic soil crust reduced infiltration.The microbiotic soil crust cover had a significant negative influence on the infiltration for rainfall events（〈14.8 mm）,restricting the infiltration depth to less than 40 cm and increasing soil moisture content just beneath the soil profile of 40 cm,whereas it was not as strong or clear for larger rainfall events.The high frequencies（84.6%） of small rainfall events（10 mm） in the Mu Us Sandland and the inhibition effect on rainfall infiltration caused by the microbiotic soil crust result in the decreased soil moisture in deeper soil layers,which makes deep-rooted subshrub Artemisia ordosica decline and facilitates shallow-rooted herbaceous species.These encouraging results imply that grazing exclusion may be efficient to reduce the existing Artemisia encroachment and facilitate the recovery toward the potential climax steppe grassland in the Mu Us Sandland.