The Research On Soil Microorganisms And Key Functional Microbes Of Nitrogen Transformation In Different Forest Land Use Types

In recent years,with the rapid increase demand of economic products such as oil,fruit and wood,a larger area of subtropical natural secondary forests have been converted into commercial forest and timber plantations,forming a variety of forest land use types.The changes in soil properties,plant species and management practices caused by the change of forest land use type affect the diversity and structure of the soil microbial community.However,how forest land use types affect soil microbial communities and key driving factors remains unclear.Therefore,we investigated soil physicochemical and biological properties of five forest land use types(secondary forest,Camellia oleifera,Amygdalus persica,Myrica rubra and Cunninghamia lanceolata plantations)in the subtropical region,selected the minimum data set,calculated the soil quality index and identified the key soil quality indicators.Besides,we analyzed the diversity and composition of soil bacterial,fungal and Ntransformation microbial communities of five forest land types by the high-throughput sequencing and qPCR techniques.Moreover,we revealed key driving factors of microbial communities’ differences by constructing structural equations model(SEM)and multiple regression model(MRM).These results were helpful to further understand the soil microbe functions,and provided the scientific basis for soil quality improvement,management and sustainable development in subtropical forests.The main conclusions are as follows:(1)There were significant differences in soil quality index(SQI)among five forest types.The SQI was in the order of secondary forest>A.persica>M.rubra>C.lanceolata>C.oleifera plantations.Soil organic carbon(SOC),glutaminase(GLS)and total phosphorus(TP)were the key indicators of the SQI.The highest SQI was observed in secondary forest,due to the higher SOC contents and GLS activities than other plantations(p<0.05).Fertilization increased total phosphorus(TP)contents in A.persica plantation,and thus improved soil quality.(2)Forest land use types affected the diversity and composition of soil bacterial communities.The a diversity of bacterial communities in A.persica,M.rubra and C.oleifera plantations were higher than others(p<0.05).The bacterial community structure of the secondary forest was different from the four plantations.The community structures of and M.rubra,C.lance olata and C.oleifera plantations were similar,respectively.Acidobacteria,Proteobacteria,Planctomycetes,Chloroflexi and Bacteroidetes were dominant taxa in five forest types.Forest land use type altered the relative abundances of Acidobacteria,Proteobacteria and Chloroflexi,and the abundances of homologous genes of amino acid,nucleotide and coenzyme function.Soil pH,carbon(C)and nitrogen(N)contents were the main driving factors for the composition and diversity of the bacterial community.(3)The diversity and composition of soil fungal communities in five forest land use types were significantly different.The α-diversities of fungal communities in A.persica and M.rubra plantations were higher than others(p<0.05).The fungal community structure of the secondary forest was different from the four plantations.The community structure of A.persica and C.lanceolata plantations were similar.Ascomycetes,Basidiomycetes and Zygomycetes were dominant taxa in five forest types.Forest land use type changed the relative abundance of C-S-R strategies fungi.For example,the relative abundance of Basidiomycetes(C-strategies)was the highest in the secondary forest,Ascomycetes(S-strategies)abundances were higher in C.oleifera,A.persica and M.rubra plantations,and the relative abundances of Zygomycetes(R-strategies)were higher in C.lanceolata,A.persica and M.rubra plantations.The alternations of fungal growth strategies may affect the decomposition ability and substrate competitiveness of soil fungi.FUNGuild results indicated that the forest land use type changed the relative abundances of functional groups,including ectomycorrhizal fungi,arbuscular mycorrhizal fungi,endophytic fungi and pathogenic fungi,and thus affected the nutrient transformation,parasitism functions and stress resistance of the fungal community.Soil pH,C and N contents were the key factors shaping the fungal community.(4)Forest land use types affected the diversity and composition of soil N2-fixing bacteria communities.The nifH gene abundance and the a diversity of N2-fixing bacteria communities were the highest in the secondary forest.The community structures of the M.rubra plantation and secondary forest were similar,indicating that the N2-fixing tree species plantation was effective to reduce the impact of forest disturbance on the community.Proteobacteria was the dominant taxa of N2-fixing bacteria communities.The change of forest land use type altered the relative abundances of dominant taxa.At the phyla level,the relative abundance of Proteobacteria was the highest in secondary forest,Cyanobacteria abundance was the highest in A.persica,and Verrucomicrobia was only presented in the M.rubra plantation.At the genera level,the relative abundances of Bradyrhizobium were higher in C.oleifera,A.persica and M.rubra plantations.Soil SOC,NH4+,total nitrogen(TN),phosphorus(P)and potassium(K)contents were the main driving factors of the soil N2-fixing bacteria community.(5)Among soil ammonia-oxidizing microbial communities in five forests,AOB played a dominant role.Forest land use type had a greater impact on gene abundance and a diversity of AO A than AOB.The a diversity of the AO A community was higher in A.persica and M.rubra plantations than the other three,while the a diversity of the AOB community was the highest in secondary forest.The community structures of AOA and AOB in the secondary forest were different from the other plantations,and the community structures of AOA and AOB in A.persica and M.rubra plantations were similar.It suggested that the similarity of the community structure of soil ammonia oxidizers may be affected by the management practices.Crenarchaeota and Thaumarchaeota were the dominant taxa of AOA.The relative abundance of Crenarchaeota was the highest in the secondary forest,and Thaumarchaeota abundances of A.persica and M.rubra plantations were higher than others.Proteobacteria was the dominant taxa of the AOB community,and its’ abundance was the highest in the secondary forest.Forest land use type altered the composition of the ammonia-oxidizing microbial community,and soil pH,NH4+ and SOC were the main driving factors.(6)Soil pH,SOC and GLS were the main factors driving the differences in soil fungal and bacterial communities among five forest land use types.Soil SOC,TN,NH4+and GLS were the main factors affecting the difference of soil N2-fixing bacteria community.Soil SOC,TN,NH4+,UR and GLS were the key factors driving the differences of the ammonia-oxidizing microbial community.(7)Land reclamation and removal of litter and understory vegetations accelerated the loss of soil C and N contents,resulting in the degradation of soil quality,and affecting the growth strategies and community of soil microbes.Thus,the SOC content could be increased by increasing litter cover and soil organic matter input,the GLS activity and phosphorus content of soil could be increased by applying N fertilizer and mineral compound fertilizer,which was beneficial to the improvement of soil quality of plantations.The application of organic fertilizer and mineral compound fertilizer can increase exogenous microbes and soil nutrients(P,K et.al),which is beneficial to improve soil microbial diversity.The planting of N2-fixing tree species was conducive to the community construction of soil N2-fixing bacteria community.