Background:Soil aggregates are the basic units of soil structure,and their stability is a key indicator of soil quality and capacity to support ecosystem functions.The impacts of various environmental factors on soil aggregates have been widely studied.However,there remains elusive knowledge on the synergistic effects of changing forest stand structure on soil aggregate stability(SAS),particularly in subtropical China where soil erosion remains a critical issue.Methods:We investigated variations in the components of soil humus(HS),including humic acids(HAs),fulvic acids(FAs),and humins(HMs),under pure Chinese fir(Cunninghamia lanceolata)plantation(PP)and multi-layered mixed plantation(MP)comprising C.lanceolata,Castanopsis hystrix,and Michelia hedyosperma.The state of soil aggregate stability,was determined by three separate methods,i.e.,dry-sieving,wet-sieving,and the Le Bissonnais.High-throughput sequencing was used to determine the diversity and composition of microbial communities under PP and MP.We then built partial least squares path models(PLS-PM)for assessing the re-sponses of SAS to the variations in soil microorganisms and HS components.Results:The MP stands had significantly greater SAS(P＜0.05),higher content of HAs and more rapid organic matter humification within aggregates,than the PP stands.High-throughput sequencing confirmed that the Pielou and α-diversity index values(Chaol and Shannon)for fungi were all significantly higher under MP than under PP,while no marked difference was found in bacterial α-diversity between the two plantation types.Moreover,there were markedly greater abundance of three bacterial phyla(Verrucomicrobia,Chloroflexi,and Gemnmnatimonadetes)and three fungal phyla(Ascomycota,Kickxellomycota,and Glomeromycota),and significantly less abundance of two bacterial phyla(Planctomycetes and Firmicutes)and four fungal phyla(Basidiomycota,Mortierellomycota,Mucor-omycota,and Rozellomycota)under MP than under PP.The Chlorofllexi and Ascomycota phyla appeared to be the primary drivers of soil aggregate distribution.Our findings revealed that the promotion of SAS under MP was mainly driven by increased soil organic matter(SOM)content,which altered bacterial communities and enhanced fungal diversity,thereby increasing HAs content and the rate of organic matter humification.Conclusions:Considering the combined effects of enhanced soil quality,productivity,and relevant economic costs,introducing broadleaved tree species into Chinese fir plantations can be an effective strategy for stabilizing soil structure against erosion in subtropical China.Our study elucidated the controls on variations of SAS in Chinese fir-dominated plantations and demonstrated the benefit of converting pure Chinese fir plantation to multi-layered mixed plantations in increasing soil structural stability and improving site quality.

Guannv Gao;Xueman Huang;Haocheng Xu;Yi Wang;Weijun Shen;Wen Zhang;Jinliu Yan;Xiaoyan Su;Shushou Liao;Yeming You

Guangxi Key Laboratory of Forest Ecology and Conservation,State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources,College of Forestry,Guangxi University,Nanning 530004,China;Guangxi Youyiguan Forest Ecosystem Research Station,Pingxiang,532600,Guangxi,China;School of Agriculture,Shenzhen Campus of Sun Yat-sen University,Shenzhen,518107,Guangdong China;Institute of Resources and Environment,Key Laboratory of National Forestry and Grassland Administration/Beijing for Bamboo&Rattan Science and Technology,International Centre for Bamboo and Rattan,Beijing 100102,China;Experimental Centre of Tropical Forestry,Chinese Academy of Forestry,Pingxiang 532600,Guangxi,China

森林生态系统（英文版）

[1]Guannv Gao;Xueman Huang;Haocheng Xu;Yi Wang;Weijun Shen;Wen Zhang;Jinliu Yan;Xiaoyan Su;Shushou Liao;Yeming You-.Conversion of pure Chinese fir plantation to multi-layered mixed plantation enhances the soil aggregate stability by regulating microbial communities in subtropical China)[J].森林生态系统（英文版）,2022(06):823-837

humins,hedyosperma,Gemnmnatimonadetes,Kickxellomycota,omycota,Chlorofllexi

Conversion,pure,Chinese,multi,layered,mixed,enhances,soil,stability,regulating,microbial,communities,subtropical,China,Background,Soil,aggregates,basic,units,structure,their,key,indicator,quality,capacity,support,ecosystem,functions,impacts,various,environmental,factors,have,been,widely,studied,However,remains,elusive,knowledge,synergistic,effects,changing,forest,SAS,particularly,where,erosion,critical,issue,Methods,We,investigated,variations,components,humus,HS,including,humic,acids,HAs,fulvic,FAs,HMs,under,Cunninghamia,lanceolata,PP,MP,comprising,Castanopsis,hystrix,Michelia,state,was,determined,three,separate,methods,dry,sieving,wet,Le,Bissonnais,High,throughput,sequencing,used,diversity,composition,then,built,partial,least,squares,path,models,PLS,PM,assessing,sponses,microorganisms,Results,stands,had,significantly,greater,higher,content,more,rapid,organic,matter,humification,within,than,confirmed,that,Pielou,values,Chaol,Shannon,fungi,were,all,while,difference,found,bacterial,between,two,types,Moreover,markedly,abundance,phyla,Verrucomicrobia,Chloroflexi,fungal,Ascomycota,Glomeromycota,less,Planctomycetes,Firmicutes,four,Basidiomycota,Mortierellomycota,Mucor,Rozellomycota,appeared,primary,drivers,distribution,Our,findings,revealed,promotion,mainly,driven,increased,SOM,which,altered,enhanced,thereby,increasing,Conclusions,Considering,combined,productivity,relevant,economic,costs,introducing,broadleaved,tree,species,into,plantations,effective,strategy,stabilizing,against,study,elucidated,controls,dominated,demonstrated,benefit,converting,structural,improving,site

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