Microbial Community Characteristics Of Main Forest Types At Huoditang Forest Region In The Qinling Mountains

Taking microbial communities in soils of five main forest types and in fallen woods under the sharptooth oak(Quercus aliena var. acuteserrata) and Chinese pine(Pinus tabulaeformis) forests at Huoditang forest region on the south-facing slope of the Qinling Mountains as objects, we explored the microbial diversity, distribution patterns and community characteristics of soils and fallen woods, and the relationships between microbial communities and physical and chemical properties of soils and fallen woods by combining field investigation, laboratory analyses with multivariate statistical analyses to provide a theoretical basis for protecting microbial resources and managing the forests of the Qinling Mountains. The main results are as follows:1. The wilson spruce(Picea wilsonii) forest soils had the highest microbial biomass carbon and basal respiration, the highest microbial biomass nitrogen was found in the sharptooth oak soils. The sharptooth oak-Chinese pine mixed and spruce forest soils had higher metabolic quotient. Otherwise, the highest ratio of microbial biomass carbon and nitrogen was in the spruce forest soils, while the greatest ratio of microbial biomass carbon and organic carbon and ratio of microbial biomass nitrogen and total nitrogen were found in the oak soils. The highest activities of soil invertase and acid phosphatase were in the spruce soils, but the mixed forest soils had the highest activities of urease and catalase. The tested soil microbial indices were certainly related with soil physical and chemical factors. Based on soil microbial, physical and chemical factors, the spruce and Chinese pine forest soils were more similar, other three forests had specific soils.2. The use rate of soil microbial carbon sources gradually increased with incubation time, the Armandi pine(Pinus armandi) soils had the highest metabolic activity. The microbial communities of the Armandi pine forest soils were also superior in diversity of carbon source utilization. Among the five forest types, the microbial communities of three coniferous forests had higher efficiency of carbon source utilization. Carbohydrates were the primary carbon sources for microbial communities of these forest soils, followed by amino acids and carboxylic acids. The diversity indices for carbon source utilization were closely associated with soil physical and chemical properties. The microbial communities of oak and mixed forest soils were similar in carbon source utilization characteristics, the microbial communities of two pine forest soils were similar, too, while the microbial communities of spruce forest soils were unique. Overall, the soil microbial communities of coniferous forests were higher in function diversity than those of the broadleaved and mixed forests.3. The three coniferous forest soils were superior to the oak and mixed forest soils in microbial total PLFA, bacterial PLFA, fungal PLFA and ratio of fungal PLFA/bacterial PLFA. The soil microbial total PLFA, fungal PLFA and ratio of fungal PLFA/bacterial PLFA were subjected to obvious influences from soil physical and chemical factors, but the bacterial PLFA showed negative correlation with ratio of soil carbon and nitrogen alone. The soils of the spruce forests and Chinese forests had higher similarity in microbial community structure, while other three forest soils had special community structure.4. Under two threshold combinations, the mixed forests had abundant soil fungal diversity, while the oak forest soils had the highest fungal richness. Considerable TRFs which had similar relative abundance were shared by three coniferous forest soils, while soil fungal communities of the mixed and oak forests possessed some distinctive TRFs, making the communities different from the fungal communities of the coniferous forest soils. The Chinese pine, Armandi pine and wilson spruce forests had similar soil fungal communities, but the mixed and oak forests had specific community composition. Evident modular structure of the interspecific relationship networks discriminated habitat generalist and specialist fungi from common fungi. The soil physical and chemical properties played very important roles in soil fungal community composition. Soil fungal communities of three coniferous forests were similar, while the soils of oak and mixed forests had distinctive composition of soil fungal communities.5. Coniferous forest soils had higher sand content than oak forests and mixed forests, clay and silt contents had inverse patterns. Eight soil chemical factors were lower in the oak forest soils. The forest soils of wilson spruce and Armand pine were similar in soil physical and chemical properties, the soils of oak forests were similar to those of mixed forests in soil properties, the Chinese pine soils were unique.6. The sharptooth oak and Chinese pine fallen woods at different decomposition stages significantly differed in bacterial diversity and community structure. The bacterial diversity of the oak woods followed the trend with IV > II > III > I > V, while the pine woods followed with I > II > V > IV > III. Overall, the bacterial diversity of the oak woods was higher than that of the pine woods at different stages. The first three bacterial phylums which had a high relative abundance in all, oak or pine woods were Firmicutes, Proteobacteria and Acidobacteria, respectively, and the first three bacterial classes were Bacilli, Alphaproteobacteria and Acidobacteria. The bacteria in Firmicutes(Bacilli) were the most abundant in the woods at decomposition stage I, III and V, but the least at stage II and IV. With pine wood decomposition, the relative abundance of bacteria in Firmicutes(Bacilli) increased gradually, became the highest at stage III, then decreased. At the phylum, class and genus levels, the bacterial community structure of the oak and pine woods were totally different at different decomposition stages. Co-occurrence network had an obvious modularity structure, the bacterial species composition of the woods was non-random, most of bacterial classes co-occurred each other, the strong exclusion was found between Bacilli and some classes. The physical and chemical factors influencing on patterns of bacterial communities and groups were distinct between the oak and pine woods, no specific rule was observed.7. The fungal diversity and community structure were also significantly different between the oak and Chinese pine fallen woods at different decomposition stages. The fungal diversity of the oak woods followed the trend with II > IV > V > I > III, while the pine woods followed with V > I > III > IV > II. Overall, the fungal diversity of the pine woods was higher than that of the oak woods at different stages. Only two fungal phylums which had a relative abundance over 1% in all, oak or pine woods were Basidiomycota and Ascomycota, and the first three fungal classes with a high relative abundance were Agaricomycetes, Sordariomycetes and Eurotiomycetes, respectively. For the oak woods, the fungal classes, Agaricomycetes, Eurotiomycetes and Dothideomycetes, were dominant at all decomposition stages, while the pine woods were Agaricomycetes, Sordariomycetes and Eurotiomycetes. In despite of less diversity, Basidiomycota fungi were considerably abundant, the fungal communities dominated by Ascomycota transformed to ones dominated by Basidiomycota with the oak and pine wood decomposition. At the phylum and class levels, the fungal community structure of the oak and pine woods also were similar at early decomposition stages(I and II), while the communities at middle and later stages(III, IV and V) were similar in species composition. But at the genus level, the fungal community structure was totally different at different decomposition stages. Co-occurrence network had an obvious modularity structure, but the fungal species composition of the woods was inclined to random at the order level, most of fungal orders strongly but finitely co-occurred each other, few of orders exhibited mutual exclusion. The density and moisture of the fallen woods also were the critical influential factors for fungal communities and group patterns.8. Clear differences in physical and chemical properties were found in the oak and Chinese pine fallen woods at different decomposition stages. The moisture and density of oak and pine fallen woods increased and decreased with decomposition, respectively. Among the tested 6 chemical elements, carbon and potassium contents gradually lost with wood decomposition, while the contents of nitrogen, phosphorus, calcium and magnesium increased with decomposition. The density, potassium, calcium and magnesium contents of the oak woods were higher than those of the pine woods at all decomposition stages, but carbon content had an inverse trend. The contents of nitrogen and phosphorus of the two woods did not show regular variation. For physical and chemical properties, the similarity was found in oak and pine woods at decomposition stage I. The oak and pine woods at stage II and III were similar. The oak and pine woods were similar at the stage IV and V. For the oak fallen woods, the woods at stage I, II and III were similar in the physical and chemical factors, the woods at stage IV and V had similarity. For the Chinese pine woods, the woods at stage I and II had similar physical and chemical properties, while the woods at stage III, IV and V were more similar.