Study On Soil Microbial Diversity In Jianfengling Tropical Montane Rainforest On Hainan Isand

Microorganisms are the most widely distributed group of life on earth and live in all parts of the biosphere.Soil microbes,as an important part of the ecosystem,play an major role in regulating nutrient cycling in nature,the succession of ecosystems,and the maintenance of biological diversity.Soil bacteria and fungi are the two most important groups of soil microorganisms.The estimation results of their species richness in most studies are in large differences,due to low resolution molecular methods and limited number of samples and less parametric and nonparametric estimators.More notably,there is a critical knowledge gap that few studies try to estimate the total species richness of soil bacterial and fungal in a fixed area of local habitat.In addition,a large body of envidences showed that the microbial community structure and diversity present a certain distribution pattern and which is mainly driven by environmental properties and geographical isolation.Since the relative importance of these two factor are scale dependent,it is necessary to comparing their relative importance in structuring local soil bacterial and fungal diversity.Furthermore,the current large number of soil microbial biogeographic studies is mostly focused on the description of the spatial distribution pattern of microbial communities,however,little is known about the mechanisms of soil microbial community assembly.Here,a 60 ha dynamics plot in the tropical montane rainforest in Jianfengling,Hainan Island was selected as the study site,the whole plot was divided into 500?40 m×30 m?regular grids and then each grid was further partitioned into 12 cells.Soil samples were collected from each cell?total 12 soil samples?at 0-10 cm depth and homogeneously mixed together as a single sample.Finally,total of 500 soil samples throughout the whole plot were collected.Illumina MiSeq sequencing platform was used to measure the bacterial 16S rRNA and fungal ITS2 rRNA gene sequences of 500 soil samples for quantification of soil microbial species richness,uncovered the diversity distribution and community assembly mechanisms.We aim to understand how biotic and abiotic factors determine the spatial distribution pattern of soil microbes in the tropical montane rainforest and identify and quantify community assembly process.The main conclusions in this paper are as follows:?1?We used 5 parameters and non-parameters estimators to refer OTUs?Operational Taxanomic Unit?number of soil bacterial and fungal in the plot.The analysis results show that non-parametric Chao2 estimator was the best estimator for estimating the soil bacterial and fungal OTU richness.There were at least 42828 bacterial OTUs?95%CI:42914⁴2946?and23137 fungal OTUs?95%CI:23104²3176?in the plot.?2?Based on the abundance and incidence data of OTU in all samples,use iNEXT package in software R to analyze the sample coverage.We suggest that at least 281 samples and 742767 sequences are need to estimate the soil bacterial OTU richness in 60 ha plot.However,for soil fungal,required at least 386 samples and 383189 sequences to estimate the total OTU richness in our plot.?3?Stepwise multiple regression on both soil bacterial and fungal OTU richness??diversity?were conducted.The analysis results showed that nitrate nitrogen contributed a larger proportion of the variation in soil bacterial OTU richness?15%?than that in soil fungal OTU richness?1.8%?.On the contray,spatial variables(i.e,2^nd spatial trend terms)explained a larger proportion of the variation in soil fungal OTU richness?27%?than that in soil bacterial OTU richness?19.3%?.Therefore,the spatial distribution of soil bacterial and fungal OTU richness is influenced by different factors and the distribution of them is uniform and aggregated,respectively,in 60 ha plot.?4?Stepwise multiple regression of the soil bacterial and fungal beta diversity analysis showed analogous results,indicating that nitrate nitrogen occupied a larger proportion of the variation in soil bacterial beta diversity?17.7%?than that in soil fungal OTU richness?5.8%?.On the contrary,spatial paremeters?i.e.,geographic distance?made a larger proportion of the variation in soil fungal beta diversity?13.6%?than that in soil bacterial beta diversity?9.3%?.Synthesiz these results suggest that soil environmental parameters,especially nitrate nitrogen is the main driver of diversity distribution of bacterial.In contrast,the local-scale distribution pattern of soil fungal communities is predominantly mediated by spatial distance.?5?This study further found that there was a significant positive correlation between the OTU richness of soil bacterial community and that of plant community on the ground.However,fungal OTU richness were not correlation to plant richness.Interestingly,both soil bacterial and fungal beta diversity were significant positive correlation with that of plants,and this relationship is still exist after excluding the effect of covariant environmental factors.Indicating the similar soil microbial composition was along with similar plant community composition in our plot.These results collectively mean that belowground and aboveground biodiversity are closely linked.?6?Bacterial and fungal community assembly processes were assessed by beta-mean-nearest taxon distance?betaMNTD?and beta-nearest taxon index?betaNTI?.Our results found that homogeneous selection and dispersal limitation are the main process driving the community assembly of soil bacterial?72%?and fungi?67.8%?,respectively,in our plot.Dispersal limitation also contribute 26%to the community assembly of soil bacteria.Variable selection explained 23.4%to the community assembly of soil fungi.Moreover,1.8%and 8.3%of community assembly of soil bacterial and fungi were contributed by ecological drift.These results further indicated that distinct mechanisms driving the community assmbly of soil bacteria and fungi.To sum up,our uniform and intensive sampling studies in 60 ha dynamics plot in the tropical montane rainforest accurately estimate the enormous soil bacterial and fungal OTU richness,uncovered the spatial distribution of their diversity and and its drivering factors,as well as community assembly mechnisms.This study provided a basis for the future study of relating belowground microbial communities to aboveground plant communities,functional diversity.