| In this study,natural secondary oak-pine mixed forests in Shaanxi Xin Kuang Forestry were subjected to three thinning treatments,including control(CK),4a(4 years after thinning),and12a(12 years after thinning).Soil physicochemical properties(p H,soil water content: SWC,available phosphorus: AP,available nitrogen: AN,total phosphorus: TP,total nitrogen: TN),soil enzyme activities(β-glucosidase: BG,cellobiohydrolase: CBH,invertase: INV,peroxidase: PER,phenol oxidase: POX),soil organic carbon(SOC),and labile carbon fractions(microbial biomass carbon: MBC,easily oxidizable organic carbon: EOC,and dissolved organic carbon: DOC)in four aspects to study the effects of different thinning treatments on oak-pine mixed forests in the Qinling Mountains.The results showed that:(1)Thinning improved soil physicochemical properties and increased soil p H,total phosphorus,and available phosphorus content.Soil water content and total nitrogen decreased after 4 years of thinning and improved after 12 years of thinning,which gradually returned to the unthinning stage;Soil water content,total nitrogen,and available nitrogen were influenced by soil depth and decreased with increasing soil depth,while p H,total soil phosphorus and available phosphorus were not influenced by soil depth;Seasonal changes also affected the changes of soil physicochemical properties.(2)SOC,EOC,and MBC all showed a trend of decreasing first after 4 years of thinning and then increasing after 12 years of thinning.Thinning had little effect on DOC,but different trends were observed in the spring and summer: 12a>4a>CK in May and CK>4a>12a in August;SOC,MBC,EOC,and DOC all decreased with the increase of soil layers;There were significant seasonal differences in DOC activity,and DOC was significantly higher in August than in May among all treatments in all soil layers.Correlation analyses showed that SOC,MBC,and EOC were significantly positively correlated with soil enzyme activities(BG,CBH,INV)and TN.(3)Thinning significantly reduced BG and CBH activities in the spring(May),while soil BG and CBH activities increased in the summer(August)in the surface soil.The INV,POX,and PER activities did not differ significantly after thinning in the 0-20 cm soil layer;the BG,CBH,and INV activities decreased with increasing soil layer,while POX and PER activities were not affected by soil layer depth;the BG and CBH activities differed seasonally in the 12 a treatments in the 20-40 cm soil layer and were significantly higher in August than in May.The correlation showed that soil enzyme activities(INV,BG,and CBH)were significantly positively correlated with soil physicochemical properties(SWC,TP,and TN).In summary,through the study of oak-pine mixed forests in Qinling Mountains with different recovery times after thinning,it was found that soil organic carbon and some labile fractions(EOC,MBC)showed a complex change trend,that is,after thinning,they first decreased and then increased,and soil organic carbon could reach the pre-thinning level within the long-term recovery time after thinning(12 years after thinning).This can provide a theoretical basis for studying the long-term effects of forest management on the soil carbon cycle,and help relevant departments to optimize forest thinning schemes,so as to better manage natural secondary forests. |
