Patterns And Drivers Of Soil Physicochemical Properties In Xinjiang Temperate Steppe

In grassland ecosystem,soil physicochemical properties are one of the main factors that affect plant growth and soil nutrient availability.Studying the change of soil physicochemical properties is of great reference significance for deeply understanding the relationship between soil and grassland.A large number of studies have revealed that the soil physicochemical properties of grassland were influenced by topography,climate,vegetation and other factors.However,previous studies have focused on effects of these variables on surface soil,while our knowledge about their effects on soil physicochemical properties among different soil layers was still limited.To address this knowledge gap,we collected soil physicochemical properties(soil bulk density: SBD;volume ratio of rock to soil: RRS;soil p H,soil total nitrogen content: STN;soil organic matter: SOM)at the different soil layers of 0-5,5-10,10-20,20-30,30-50,50-70 and 70-100 cm among 86 sites in Xinjiang temperate steppe in 2011-2013.We also surveyed surface features(standing litter,litter,gravel,sand covering,wind and water erosion),topography(elevation,slope and aspect)and climate(mean annual temperature: MAT;mean annual precipitation:MAP)for each site.Finally,we explored effects of surface features on soil physicochemical properties as well as relationships between soil physicochemical properties and topography,climate and soil physicochemical properties.Our results showed :Characteristics of changes and internal relations in soil physicochemical properties:(1)With the increase of soil depth,soil p H is increasing gradually,STN and SOM are decreasing.while SBD and RRS have no significant change.(2)Soil p H in each soil layer showed weak variability,while the rest of soil physicochemical properties showed moderate variability.(3)Soil total nitrogen is positively correlated with organic matter in all soil layers,while soil bulk density is negatively correlated with total nitrogen in0-50 cm soil layers and organic matter in 0-30 cm soil layers.With the deepening of soil layer,the correlation coefficient gradually decreases.Effects of surface features on soil physicochemical properties:(1)Standing litter significantly increased SBD of 5-10 cm and 10-20 cm soil layers,but decreased the p H of 0-50 cm soil layers.(2)Litter has no significant influence on SBD,RRS,p H,STN and SOM.(3)Gravel significantly reduced RRS of70-100 cm soil layer,STN of 0-10 cm soil layers and SOM of 0-20 cm soil layers,but significantly increased SBD of 5-10 cm and 20-30 cm soil layers.(4)Sand covering significantly reduced the p H of70-100 cm soil layer,STN of 0-30 cm soil layers and SOM of 0-20 cm soil layers.(5)Wind erosion significantly reduced STN and SOM in 0-5 cm and 5-10 cm soil layers,but increased SBD of 0-30 cm soil layers.(6)Water erosion significantly increased RRS of 10-20 cm and 30-50 cm soil layers and the p H of0-20 cm soil layers.Effects of topography and climate on soil physicochemical properties:(1)With the increase of elevatio,the soil p H linearly increased in each soil layer,while RRS only increased in 30-50 cm and 50-70 cm soil layers.(2)With the increase of slope,only SOM linearly increased in 20-30 cm and 30-50 cm soil layers.(3)In 50-70 cm and 70-100 cm soil layers,RRS of shady slope is significantly higher than that of semi-shady slope,semi-sunny slope and sunny slope.Except for 0-5 cm and 70-100 cm soil layers,SOM in the shady slope is significantly higher than that in the sunny slope.(4)With the increase of MAT,RRS in 10-20 cm and 30-50 cm soil layers decreased significantly,while the soil p H in 0-5 cm and 5-10 cm soil layers increased significantly.(5)With the increase of MAP,soil p H in 0-30 cm soil layers decreased significantly.Except for the 50-70 cm and 70-100 cm soil layers,STN increased linearly in each soil layer,while SOM only increased significantly in the 0-5 cm topsoil.