Diciphering The Mechanisms For Bacterial Community Assemblage In Fire-altered Forest Soil With Regard To Pyrogenic Organic Matter

Pyrogenic Organic Matter(PyOM)is a broad continuum of carbon-enriched substances characterized by semi-charred biomass,charcoal and soot generating in vegetation fires.Current studies on anthropogenic PyOM(i.e.biochar)show its porous structure and recalcitrance to degradation provide lasting habitat for species,and addition of PyOM has substantial impact on the structure of soil microbiome.They lead to the hypothesis of the present study that natural PyOM generated in wild fires is also micro-habitats distinct to fire-altered soil,resulting in alterations onmicrobial assemblage processesSoil and soil-like habitats,such as plant rhizosphere and sediment,harbor the highest microbial diversity in our planet-an extreme richness that has been long recognized in fields such ecology,microbiology and soil science,however,our knowledge and understandings towards the mechanisms behind species coexistence in soil are limited.In co-existence theory,the niche-difference stabilized the coexistence of species and heterogeneous environment condition could provide extra niche dimensions and promote co-existence of species.Thus,we further suppose that the spatial assemblage of microbiome with regard to soil-PyOM habitat difference would prompt the microbial diversity in fire-altered soil.Soil and PyOM samples used in the present study were from two typical fire-altered forest sites in Fuyang,Zhejiang province and Yingtan,Jiangxi province.We focus on the heterogeneity of PyOM and adjacent soil and discuss on the contribution of spatial assemblage and coexistence to soil microbial diversity.The global ubiquity of forest wildfires results in the generality of forming PyOM.The component difference of PyOM to soil also makes it an ideal material to study microbial assemblage.Therefore,this study aims to:(1)develop an effective and reliable method to isolate PyOM from fire-altered soil in order to characterize the physiochemical properties and microbial communities in PyOM(as well as fire-altered soil and unburnt soil),(2)analyze the assemblage processes of soil microbial community,select specialists and generalists of PyOM-soil heterogeneity and describe the specialists,and(3)develop a new phylogenetic algorithm to analyze the coherent lineages of specialists,analyze the niche of the lineages by literature reviews,and use simulations to verify the contribution of spatial assemblage and co-existence of specialists to biodiversity.The main results are as follows:(1)Burnt soil had higher biodiversity than unburnt soil and they had different microbial community structure.Soil pH increased and dissolved organic matter decreased after wildfires,but there was no difference in soil organic matter.The PyOM particles(habitat patches)were separated from burnt soils with a typical diameter ranging from 0.1mm to 10mm.They had distinct environmental pH and microbial community structure from adjacent burnt soil.Unconstraint ordination(based on generalized UniFrac and Non-metric MultiDimensional Scaling,NMDS)showed there was a significant gradient between unburnt soil,burnt soil and PyOM.(2)Specilists of soil and PyOM were selected using differential abundance analysis and they made up of 69%and 82%of the PyOM-soil gradient at Fuyang and Yingtan sites,respectively,as measured by a sensitivity analysis.Co-occurring network showed that soil and PyOM specialists were connected with each other by strong negative relations while the specialists of the same types were clustered as some modules.Phylogenetic analysis showed that specialists had very siginificant phylogenetic signals.(3)Further analysis of phylogenetic coherence showed that optimum growth pH of operational specialists was globally convergent.Coherent clusters of PyOM specialists were neutrophilic to slightly alkaliphilic but those for soil specialistswere usually acidophilic and occasionally neutrophilic.Procrustes analysis showed there were strong relations between PyOM patch and its adjacent soil.Further simulations based on PyOM-soil mosaic model yielded microbial community structures and biodiversity indices similar to the real burnt soil samples.