Conversion of pure Chinese fir plantation to multi-layered mixed plantation enhances the soil aggregate stability by regulating microbial communities in subtropical China

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 multilayered 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 responses 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 andα-diversity index values(Chao1 and Shannon)for fungi were all significantly higher under MP than under PP,while no marked difference was found in bacterialα-diversity between the two plantation types.Moreover,there were markedly greater abundance of three bacterial phyla(Verrucomicrobia,Chloroflexi,and Gemmatimonadetes)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,Mucoromycota,and Rozellomycota)under MP than under PP.The Chloroflexi 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.

Upgrade from aerated static pile to agitated bed systems promotes lignocellulose degradation in large-scale composting through enhanced microbial functional diversity

Composting presents a viable management solution for lignocellulose-rich municipal solid waste.However,our understanding about the microbial metabolic mechanisms involved in the biodegradation of lignocellulose,particularly in industrial-scale composting plants,remains limited.This study employed metaproteomics to compare the impact of upgrading from aerated static pile(ASP)to agitated bed(AB)systems on physicochemical parameters,lignocellulose biodegradation,and microbial metabolic pathways during largescale biowaste composting process,marking the first investigation of its kind.The degradation rates of lignocellulose including cellulose,hemicellulose,and lignin were significantly higher in AB(8.21%-32.54%,10.21%-39.41%,and 6.21%-26.78%)than those(5.72%-23.15%,7.01%-33.26%,and 4.79%-19.76%)in ASP at three thermal stages,respectively.The AB system in comparison to ASP increased the carbohydrate-active enzymes(CAZymes)abundance and production of the three essential enzymes required for lignocellulose decomposition involving a mixture of bacteria and fungi(i.e.,Actinobacteria,Bacilli,Sordariomycetes and Eurotiomycetes).Conversely,ASP primarily produced exoglucanase andβ-glucosidase via fungi(i.e.,Ascomycota).Moreover,AB effectively mitigated microbial stress caused by acetic acid accumulation by regulating the key enzymes involved in acetate conversion,including acetyl-coenzyme A synthetase and acetate kinase.Overall,the AB upgraded from ASP facilitated the lignocellulose degradation and fostered more diverse functional microbial communities in large-scale composting.Our findings offer a valuable scientific basis to guide the engineering feasibility and environmental sustainability for large-scale industrial composting plants for treating lignocellulose-rich waste.These findings have important implications for establishing green sustainable development models(e.g.,a circular economy based onmaterial recovery)and for achieving sustainable development goals.