Characteristics of soil enzyme activity and nutrient content and their correlations at different succession stages of broadleaf-Korean pine forest

We studied the enzyme activity in each soil layer (A1, B, and C) and its relationship with soil nutrient availability and active organic carbon to provide scientific proofs for soil fertility evaluation in the process of progressive succession (formation stage, development stage, stability stage, and climax community) in broadleaf and Korean pine mixed forest in the Xiaoxing’anling Mountains by using comparative analysis. The results showed that, the activities of soil enzymes of urease, invertase, catalase and polyphenol oxidase in A1 layer were all significantly higher than in B and C layers in the process of progressive succession. However, the activities of urease, invertase, catalase and polyphenol oxidase in A1 layer were higher to varying degrees in the formation stage than in the development stage. The variation in polyphenol oxidase activity presented a decreasing trend as succession stage progressed. There existed correlations between soil nutrients with activity of soil enzymes urease, invertase, and catalase and polyphenol oxidase. There were highly significant correlations between soil urease, invertase, and rapid K, available P, organic matter, and total N, respectively, but significant correlations between activity of catalase, polyphenol oxidase, and total N, rapid K, available P, and organic matter, respectively. In addition, there was a significant correlation between the activity of urease, catalase, polyphenol oxidase with labile organic carbon and microbial biomass carbon, respectively, but no significant correlation with dissolved organic carbon. The correlations of invertase activity with three types of organic carbon all reached significant level. Soil enzyme activity and nutrient characteristics can be used as comprehensive indexes, which indicate soil fertility levels of different succession in the Xiaoxing’anling region.