Objective To study the effects of different understory vegetation management measures on soil enzyme activities and quality in Cunninghamia lanceolata large-diameter industrial plantation.

Method Taking Cunninghamia lanceolata large-diameter industrial plantation as the research object, This study analyzed soil enzyme activities of plantation under three kinds of understory vegetation management measures, i.e. understory vegetation protection (UP), understory vegetation removal (UR) and understory interplanting (IP). The integrated quantitative evaluation on soil quality was made by principle components analysis taking soil enzymes as soil biological activity indexes combining with soil physical and chemical characteristics.

Result The IP increased the sucrase activity in the soils with the depth of 0-20 cm, and there was no obvious difference between the sucrase activity in the soils with the depths of 20-40 and 40~60 cm under these understory vegetation management measures. Compared with UR and IP, the UP showed better effect in increasing soil catalase activity and decreasing soil urease activity, and the soil urease and catalase activity under UR and IP showed no obvious difference. The ranking of soil acid phosphatase activity under the three kinds of understory vegetation management measures was IP>UR>UP, and the ranking of soil polyphenol oxidase activity was UP>IP>UR. The activities of urease, sucrase and polyphenol oxidase in soil under different understory vegetation management measures showed a big difference, and the response of polyphenol oxidase to understory vegetation management measures was more sensitive and was reflected in deeper soil layer. Except acid phosphatase activity, the activities of other soil enzyme showed a obvious property of surface-aggregation, and decreased with the deepening of soil layer. The contents of organic matter and hydrolyzed nitrogen showed extremely significant or significant positive correlation with the activities of the 5 kinds of soil enzyme, the content of available phosphorus showed extremely significant positive correlation with the activities of sucrase, urease and acid phosphatase, and the content of available potassium showed extremely significant positive correlation with the activities of sucrase, catalase and polyphenol oxidase, the activities of soil enzymes were less dependent on the soil physical properties. Soil enzyme activity was taken as one of soil quality indexes, combining with soil physical and chemical characteristics, three principal components were extracted through principal component analysis, reflecting 75.31% of the original information amount. The ranking of soil quality index among different understory vegetation management measures was IP>UP>UR.

Conclusion To sum up, in the large diameter Cunninghamia lanceolata plantation, the effect of planting Phoebe bourmei under the plantation is the best to maintain and improve the soil quality, followed by protecting understory vegetation, and the effect of understory vegetation removal is poor.