| The Loess Plateau is the region in China where soil erosion is the most severe.With the implementation of the "returning farmland to forests and grasslands" strategy,the increase in soil organic matter resulting from vegetation restoration may strengthen soil water repellency(SWR),causing interference with rainfall infiltration and an increase in the risk of soil erosion.In order to understand the performance of soil water repellency during grassland restoration on the Loess Plateau and its influencing factors,this study conducted field investigations and laboratory studies on five different restored grasslands(13 years,22 years,31 years,39 years,and 50 years)in the Yunwu Mountain Protected Area,Ningxia.Through vegetation investigation and in-situ measurement of soil water droplet penetration time(WDPT),SWR was characterized.Then,soil physical and chemical properties and microbial characteristics of grassland were studied by collecting soil samples from 0～3 cm and 3～10 cm depths.Linear correlation analysis,redundancy analysis,and path analysis were used to analyze the differences in water repellency and explore the key influencing factors of SWR in the region,providing scientific support for vegetation restoration in the loess hilly area.The results showed that(1)In the study area,the soil water repellency(SWR)of the restored grassland soil was absent at 13 years and slightly present at 22-50 years.The subsoil at depths below 3 cm did not display any SWR.The WDPT distribution range of the grassland topsoil varied from 3.71 to 54.13 s across different restoration periods.The average WDPT sequence was as follows:13 years < 22 years < 31 years <39 years < 50 years.(2)In the study area,a total of 14 families,23 genera,and 32 species of plants were recorded,mainly belonging to Asteraceae,Rosaceae,Lamiaceae and Poaceae.Plant species diversity showed little correlation with SWR,and there was no significant correlation between aboveground biomass and SWR(P>0.05).However,underground biomass was significantly negatively correlated with SWR(P<0.05),indicating that roots have an important influence on SWR.(3)Different restoration years of grasslands showed an extremely significant positive correlation(P<0.01)between SWR and soil water content,and a significant positive correlation(P<0.05)with the content of aggregates with particle sizes of 0.5～1 mm.In addition,total nitrogen and nitrate nitrogen were significantly positively correlated with WDPT index(P<0.05),but their effect on SWR weakened when the concentration was too high.Soil organic carbon,available potassium and available phosphorus,p H and ammonium nitrogen had a weak impact on SWR.(4)The SWR of the restored grasslands was highly negatively correlated with soil microbial biomass carbon(P<0.01)and significantly negatively correlated with soil microbial biomass nitrogen(P<0.05).The activity of catalase was highly negatively correlated with SWR(P<0.01),while urease activity was highly positively correlated(P<0.01).The alpha diversity index of bacterial communities in the soil was highly positively correlated with SWR(P<0.01),indicating that the higher the richness and diversity of bacterial communities,the greater the SWR.At the phylum level,the Gemmatimonadetes and Patescibacteria phyla were highly positively correlated with SWR(P<0.01).At the genus level,Sphingomona and Bryobacter were significantly negatively correlated with SWR(P<0.05),indicating that the bacterial community also has a significant impact on SWR.(5)The factors that explained the variance by more than 10% in redundancy analysis were soil moisture content(72%),total nitrogen(63.6%),nitrate nitrogen(12.7%),underground biomass(12.4%),the Simpson diversity index of bacterial communities(71.4%),Gemmatimonadetes(44.6%),and Patescibacteria(29.2%).The path analysis decision coefficient results revealed that important factors affecting SWR in the region were the Simpson diversity index of bacterial communities,Patescibacteria,total nitrogen,soil moisture content,and nitrate nitrogen.These factors can help evaluate and predict changes in SWR during grassland restoration,providing a basis for vegetation restoration and soil erosion control in the Loess Hilly Region. |
