Study On Characteristics Of Soil Microbial Community And Response Mechanism Under Different Silvicultural Measures In Pinus Massoniana Plantations

There is a strong interaction between the aboveground and belowground of the forest,soil microorganisms of belowground of forest play an important role in biogeochemical cycling.So Microbial community is a sensitive index to characterize the material cycle,health status and ecological service function of forest ecosystem.The poor forest management will result in the decrease of forest productivity,the loss of nutrients and the decrease of biodiversity.Therefore,this study selected the typical subtropical of Masson pine plantation as the research object,in 2013 September in Jinglingtou of Zigui Province Masson pine plantation,set up 3 kinds of silvicultural measures and control plots,every forest plot 10m×10m,6 replicates per treatment,24 plots.The treatments as follows: Shrub moving(SM)-shrubs of plots were totally cleared;light harvesting(LH)-within the plot DBH over 4 cm non-Masson(mainly for Betula luminifera,sumac)and some tall shrubs(Litsea,Pyracantha etc.)were cleared,the cutting intensity was 15%.Severe Harvesting(HH)-Masson Pine with DBH over 17.9cm of plots were cleared,strength of 70%.This study used high-throughput sequencing technology to obtain the whole sequence of soil microbial community structure information,get the composition,structure and function of soil microbial community characteristics through the database,combining with the environmental factors,functional characteristics,molecular ecology network model and phylogenetic characteristics,to analysis of stability of soil microbial community structure under different silvicultural measures and response mechanism.The main conclusions are as follows:1)Based on the soil microbial biomass carbon and nitrogen analysis showed that soil microbial biomass carbon and nitrogen had a significant response to silvicultural disturbance,microbial biomass carbon and nitrogen decreased significantly in the forest disturbance;and fungi than bacteria had higher microbial biomass carbon and nitrogen ratio,indicating fungi than bacteria were more sensitive to forest disturbance.2)The high-throughput sequcencing got microbial community composition and structure,diversity characteristics of bacteria and fungi showed that a high abundance species dominated community characteristics;in more subdivision level could accurately reflected the microbial responsed characteristics;silvicultural measures reduced the total number of species(OTU),in addition shrub moving and severe harvesting had a higher percentage of unique species(OTU),but linght harvesting reduced the percentage of unique species(OTU);microbial community structure significant changed(p<0.05),linght harvesting of bacterial and fungal diversity and abundance of alpha decreased significantly(p<0.05)3)The PICRUSt prediction function of family characteristics of bacteria,FUNGuild prediction nutrition and functional characteristics of fungi,results show that forest disturbance function family of bacteria showed a downward trend,only the cell communication and sensing system was significantly decreased(p<0.05);functional group of fungi was significant difference.The results showed that the bacteria had some functional redundancy,so the response was not significant,but the fungi had slow growth and host specificity,so they were more sensitive to disturbance in forest management.4)Multiple stepwise regression analysis of soil microbial biological carbon nitrogen,microbial community structure and environmental factors showed that environmental factors were driving the soil microbial heterogeneity,main controlling factors of soil microbial heterogeneity;Biological and non-biological environment factor drived the heterogeneity of the microbial community,biological factors(fine root biomass and litter production)and abiotic factors(water content,PH,stability and ammonium nitrogen)was associated with a significant microbial biomass carbon,microbial biomass nitrogen and soluble carbon significant correlation.Above showed that the environment characteristics of microbial community played a decisive role,which conformed to the theory of ecological niche..5)Through the the weak interaction got microbial molecular ecology network model,it showed that the silvicultural measures changed the network structure characteristics of microbial environment,through microbial cooperation to deal with environment interference in the forest;the key species of bacteria inside the module(module hub)decreased significantly,the key bacterial species between the modules(connected)also decreased;at the same time,fungal network model(niche)had a decline in the number of modules within the species increase.In summary: forest disturbance significantly reduced the number of niche,the same niche of species richness increased,microbial community internal competition,when the disturbance of environment,microbial community structure was not stable;in the microbial network model of environmental factor played a key role,which was in line with the theory of ecological niche.6)Through the system of microbial community phylogenetic development characteristic analysis showed that: NRI index and NTI>0 of phylogenetic developmental index of microbial system,ecological niche theory played a leading role in the process of building a microbial community,the environment was the main controlling factor limiting the soil microbial community structure;light harvesting niche amount decreased significantly,which was attributed to the light harvesting leading to microbial survival needs nutrient and energy diversity decreased;but the environment certainty effects of severe harvesting decreased significantly,mainly severe harvesting provided a lot of niche for other species update,random distribution and diffusion of neutral theory strengthened.Conclusion the above main findings: soil microbial response factor was sensitive to forest disturbance;silvicultural measures in different degree changed the community characteristics of soil microbial community characteristics;at the same time,forest disturbance by changing environmental factors to change of soil microorganisms,environmental factors were the main control factors of the microbial community structure;silvicultural measures due to the change of soil microbial network model,reduced network structure stability of soil microorganisms,microorganisms affected by environmental change,the microbial community structure was more stable;silvicultural measures leaded to the phylogenetic index of soil microbial characteristics,ecological niche of soil microbial community changed significantly.Environmental factors were main controlling factors of the microbial community,that was the niche theory;light harvesting caused niche of microbial reduction,severe harvesting for shrub and grass provided niche,which tended to random distribution,diffusion.