Soil nutrients and enzyme activities in different types of forest plantations in karst degraded mountainous sites
Artificial vegetation restoration is one of the significant ways of ecological restoration in degraded karst mountainous areas.We investigated soil nutrient contents and soil enzyme activities and their correlations across three types of forest plantations,including Cupressus duclouxina forest,Robinia pseudoacacia forest,and C.du-clouxina-R.pseudoacacia mixed forest,with unplanted land(control).We aimed to provide a reference basis for selecting suitable planting species and methods to improve soil quality in this region.The results showed that:(1)soils of all four vegetation types were alkaline,and soil pH of plantations was significantly lower than that of the un-planted land.The contents of organic matter,total nitrogen,alkali-hydrolyzed nitrogen,and available phosphorus in the soil of plantations were significantly higher than that of the unplanted land,while the contents of total potassi-um and available potassium were significantly lower than that of unplanted land.(2)Except for alkaline phospha-tase,the activities of other four enzymes were the highest in C.duclouxina-R.pseudoacacia mixed forest.The acti-vities of urease,alkaline phosphatase,and catalase in plantations were higher than those in the unplanted land.(3)The main factors influenced by soil nutrients were different for urease,polyphenol oxidase,sucrase,and alkaline phosphatase,while the correlation between peroxidase activity and nutrient indicators was not significant.(4)Re-sults of redundancy analysis showed that soil total nitrogen and phosphorus contents had significant effects on soil enzyme activities in different types of plantations,which could explain 60.7％of the variation of enzyme activities.The cumulative contribution rate of variance of enzyme activity and nutrient characteristic relationship was 78.8％.Artificial vegetation restoration in degraded karst mountainous sites could improve soil nutrient contents and enzyme activities,thereby improving soil quality,and then lay the foundation for further improving the service functions and stability of plantation ecosystems and promoting the quality of regional ecological environment.
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