Characterization Of Soil Microbial Communities In Cunninghamia Lanceolata Plantations Of Different Ages

Cunninghamia lanceolata is one of the major fast-growing timber species in Southern China.The area and stocking volume of pure Cunninghamia lanceolata plantation forests ranked first in the country in terms of tree plantation forests,respectively.Cunninghamia lanceolata plantations can not only increase the supply of timber,it also plays an important role in ecosystem service functions such as carbon sequestration and sink,water harvesting,etc.The long-term plantation mode of pure artificial forest,coupled with the coniferous species itself,Cunninghamia lanceolata plantation forests face a more common phenomenon of ground strength decline.Therefore,it is important to identify the soil evolution pattern and its internal mechanism during the development of Cunninghamia lanceolata plantation forests for different development stages.In the present study,7-,15-,and 26-year-old pure Cunninghamia lanceolata plantations were selected from a Cunninghamia lanceolata plantation in Lutou Forest in Yueyang,Hunan Province,in the central subtropical region.Stand description factors were investigated,and soil samples from different soil layers were collected,and the effects of stand age on soil physicochemical factors,microbial load carbon,nitrogen,phosphorus and soil enzyme activity as well as soil bacterial and fungal community characteristics were analyzed.To study the main factors affecting the structural changes of soil microbial communities through RDA redundancy analysis,and to elucidate the main patterns of soil fertility changes and their interrelationships with soil microbial communities during the development of Cunninghamia lanceolata plantation forests from 0 to 30 years,so as to reveal the main drivers of soil microbial changes during the development of Cunninghamia lanceolata plantations and their mechanisms and to provide a theoretical basis for the management and sustainable development of Cunninghamia lanceolata plantation forests in the central subtropical region.The results of the study showed that:(1)With the increase of forest age,Soil carbon(TOC),nitrogen(TN)and phosphorus(TP)contents showed an overall trend of Cunninghamia lanceolatast decreasing and then increasing.The mean values of TOC,TN and TP in young stands(7a)were 15.71 g·kg-1,1.96 g·kg-1 and 0.41 g·kg-1,respectively,while the TOC content in middle-aged stands(15a)was lower than that in young stands and significantly lower than that in mature stands(26a).Soil microbial biomass carbon(MBC)and microbial biomass phosphorus(MBP)content followed the same trend as TOC and TP content,while microbial biomass nitrogen(MBN)content gradually decreased with increasing stand age(190.44 mg·kg-1>124.08 mg·kg-1>101.74 mg·kg-1).C:N,C:P,MBC:MBN,and MBC:MBP gradually increased with the age of the forest,and N:P and MBN:MBP showed a trend of increasing and then decreasing.(2)Soil sucrase(SUC),urease(URE),acid phosphatase(ACP)and catalase(CAT)activities showed a significant decrease with increasing stands age.A two-way ANOVA of stand age and soil depth on soil enzyme activity in Cunninghamia lanceolata forests showed that the effects of stand age and soil depth on the activities of all four soil enzymes were significant(p<0.01),and soil layer× stand age had significant effects on SUC and URE(p<0.01),while the effects on ACP and CAT were not significant.The Cunninghamia lanceolatast two axes of RDA redundancy analysis explained a total of 93.79%of the variance in the variables,where MBC:MBN,Silt,MBN,Soil moisture content(MC),MBP,TN,TOC,and C:P were the main influences affecting SUC,URE,CAT,and ACP.(3)There are significant variability of Alpha diversity index of soil bacterial community in Cunninghamia lanceolata plantation forest between different stand ages.Chao 1,Shannon index showed significantly higher in middle-aged and mature stands than in young stands,while the difference between middle-aged and mature stands were not significant.The changes in Chao1 and Shannon index of soil fungal communities in Cunninghamia lanceolata plantations of different ages were not significant.Adonis analysis of Beta diversity of soil bacterial and fungal communities showed that the similarity of soil bacterial and fungal community structure between different forest ages was low,and the differences in community structure were significant(R2=0.3505,Stress=0.1118;R2=0.23 42,Stress=0.097),indicating that stand age has an important effect on the structure of both soil bacterial and fungal communities in Cunninghamia lanceolata plantations forests.The main dominant bacteria in the soil bacterial community were the dominant taxa Proteobacteria,Chloroflexi,Planctomycetes and Elusimicrobia of the main dominant groups of the soil bacterial community at the phylum level showed significant differences between the different stand ages.The dominant phylum Ascomycota and Rozellomycota of the soil fungal community differed significantly between stand ages,while Basidiomycota did not differ significantly between stand ages.(4)RDA redundancy analysis of soil microorganisms with soil nutrients,microbial load carbon,nitrogen and phosphorus,enzyme activity and stoichiometric ratios showed,MC,TP,MBC,MBC:MBN,MBC:MBP,MBN:MBP,Silt and Clay were the main factors affecting the variation of soil bacterial communities.Therefore,the main factors affecting the change of soil bacterial community and fungal community during the development of Cunninghamia lanceolata plantations were different.Changes in the soil bacterial community were influenced by more soil factors than the fungal community.Soil nutrients showed a large decreasing trend in the middle-aged Cunninghamia lanceolata plantation forest stage,and some dominant taxa of soil microorganisms also showed significant differences in the middle-aged forest stage,which may be related to the intense nutrient competition relationship in the middle-aged forest stage.Therefore,in the process of Cunninghamia lanceolata plantation management,we should pay attention to the management of the middle-aged forest to improve the release and absorption of active oxygen elements in the soil of Cunninghamia lanceolata plantation at the middle-aged stage.