Effects of Stand Density on Soil Physicochemical Properties and Enzyme Activities in Robinia seudoacacia Plantations in the Loess Hilly-Gully Region
[Objective]The aims of this study are to determine the appropriate stand density,and to provide the reference for implementing effective restoration practices for improving soil quality of Robinia pseudoacacia plantation in the hilly and gully region of the Loess Plateau in China by analyzing the response of soil physicochemical properties and enzyme activities to stand density changes and the relationship between soil physicochemical properties and enzyme activities.[Methods]R.pseudoacacia plantations of three stand density classes-low density(900 trees/hm2),medium density(1 200 trees/hm2),and high density(1 500 trees/hm2)density-were sampled in the Xiannangou watershed of Ansai County in loess hilly-gully region of northern Shaanxi Province,China.We analyzed the effects of stand density on soil physicochemical properties,enzyme activities,and determined the relationship between soil physicochemical properties and enzyme activities by redundancy analysis.[Results](1)Compared to low-and high-density plantations,medium density plantations significantly increased soil water content,soil organic carbon,soil total nitrogen,soil available phosphorus,and soil nitrate nitrogen.(2)With the increasing in stand density,the soil enzyme activities,including β-glucosidase,cellulase,invertase,polyphenoloxidase,catalase,urease,leucine aminopeptidase,and N-acetyl-β-glucosaminidase decreased first and then increased,and were the lowest at medium density plantations.(3)Pearson analysis showed that soil enzyme activities related to carbon,nitrogen,and phosphorus cycle negatively were correlated with the content of the corresponding resource.(4)Results of redundancy analysis showed that soil organic carbon,total nitrogen,and total phosphorus had significant effects on soil enzyme activities.Soil organic carbon,total nitrogen,and total phosphorus explained 59.8％(p＜0.01),20.8％(p＜0.01),and 9.5％(p＜0.05)of the variation of soil enzyme activities,respectively.[Conclusion]Medium density(1 200 trees/hm2)can help to conserve soil nutrient and water of R.pseudoacacia plantation,and thus is a suitable stand density management strategy for R.pseudoacacia plantations to improve soil quality.Furthermore,managers should pay attention to the changes in soil organic carbon content to implement stand density controlling to improve soil enzyme activity and hence enhance soil nutrient availability and promote the improvement of R.pseudoacacia plantations.
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