Effect Of Shrubification On Rainfall Interception And Storage Capacity Of Enclosed Grasslands On The Loess Plateau

Shrub encroachment is widespread in the arid and semi-arid grasslands of northern China.With the shrub encroachment,the plant community composition,litter and soil physical and chemical properties have been changed,which directly affects the interception and storage rainfall function of grassland ecosystem.This study assessed the characteristics of potential vegetation interception,litter and soil water holding capacity of the primary grassland and shrub-encroached grassland（including grass patch,sub-shrub patch and shrub patch）on the Loess Plateau.We further observed the relationship between plant community,litter biomass and soil physicochemical property with these grassland ecohydrological characteristics.The main results are as follows:（1）Shrub encroachment increased the grassland vegetation interception of precipitation,but decreased the vegetation interception efficiency.The capacity of vegetation interception in subshrub and shrub patches were increased by 68.4%and 179.0%,respectively.Compared with primary grassland,the efficiency of vegetation interception in herb-,subshrub-and shrub patches were decreased by 30.2%,31.7%and 22.5%,respectively.The enhanced vegetation interception was mainly derived by increasing aboveground biomass,especially plant stem biomass,while the reduction in vegetation interception efficiency was attributed to decreasing plant richness.（2）The water holding capacity of litter layer is related to the litter biomass and its decomposition status.The water holding capacity was significantly positively correlated with the litter biomass and thickness.Compared with primary grassland,the total litter biomass decreased by 64.9 g·m^-2 of shrub patch,which is mainly caused by the reduction in semi-decomposed component.The litter water holding capacity and its efficiency of shrub patch were 0.5 mm and 20.8%lower than those of primary grassland,respectively.Compared with primary grassland,the litter water holding efficiency decreased by 14.7%in undecomposed litter,and decreased by 21%in semi-decomposed in shrub patches.（3）Shrub encroachment improved the soil physicochemical properties and soil water holding capacity of shrub patch.Compared with the primary grassland,the soil bulk density of shrub patch decreased by 6.7%,the total porosity increased by 3.8%,the content of meso-aggregates increased by 12.5%,and the organic matter increased by 22.2%of 0-20 cm layer.Compared with primary grassland,the soil water holding capacity of shrub patch increased by5.3 mm,respectively.However,in sub-shrub patches,the total porosity decreased by 2.8%and the soil water holding capacity decreased by 3.3 mm,respectively.（4）The soil accounts for 98.9-99.4%of the grassland ecosystem rainfall interception and storage,which is the major regulator for grassland to mediate precipitation redistribution.Plant patches have different interception and storage effects.Under the present shrub coverage（43.3-48.5%）,the total rainfall interception and storage of grass and sub-shrub patches eroded by 3.6 mm and 3.2 mm,respectively,while the shrub patch improved by 5.1 mm compared with the primary grassland.Although shrub encroachment promoted the grassland precipitation vegetation interception,the effects of shrub and sub-shrub expansion on the water holding capacity of grassland litter and soil were contrasting.Sub-shrub expansion led to a decrease in soil water storage capacity,while shrub expansion weakened the litter water holding capacity,but increased soil water storage capacity.Therefore,it is necessary to distinguish between sub-shrub and shrub expansion in order to accurately evaluate the effect of shrubification on ecological precipitation interception and holding capacity of grassland ecosystems.