Distribution Of Microbial Group Based On Cell Size And Their Ecological Functions In Two Farmlands

The cell size of microorganisms,one of the most fundamental and important characteristics,affects the physiological metabolism and ecological functions of microorganisms.The cell size of microorganisms in the environment varies greatly,however,the ecological significance of microorganisms of different sizes in farming systems is still not fully appreciated.In this study,five groups based on cell size,including F1（>10μm）,F2（3-10μm）,F3（1-3μm）,F4（0.4-1μm）and F5（0.2-0.4μm）,were obtained from soils of maize and soybean,respectively,by using filters with five diameters（10μm、3μm、1μm、0.4μm、0.2μm）.The composition and diversity of bacteria,archaea and fungi of each size group were clarified by 16S r RNA and ITS r RNA gene high-throughput sequencings.The microorganisms of different group and their mixtures were added to the sterilized soil for incubation,and their effects on soil nutrients and enzyme activities were analyzed,and the effects of different crops cultivation on the community distribution and potential functions of different group combination were clarified.The main results are as follows:（1）High-throughput sequencing results show that the composition and community diversity of different microbial group vary by cell size.Proteobacteria was predominated in all groups.Different species analysis results show that Myxococcota,Cyanobacteria,Entotheonellaeota,Lasiosphaeriaceae,and Claroideoglomeraceae are mainly present in groups F1 and F2;Planctomycetota and Chloroflexi were mainly found in group F3,while Firmicutes,Verrucomicrobiota,Actinobacteriota and Acidobacteriota were mainly found in groups F4 and F5.The group F4 had the highest richness index and diversity index for bacterial communities,while group F1 had the highest diversity index for fungal communities among the all-size groups.The assembly process of bacterial communities of each size cell group was mainly influenced by deterministic processes,while those of fungal communities was mainly influenced by stochastic processes.Further analysis showed that different crops cultivation influenced the distribution of each size of the microbial group,for example,Abditibacteriota and Nitrospirota were characteristic differential species in the F3 group of maize cropland soils,but not in soybean cropland soils.（2）The microorganisms of each size group were incubated individually in sterilized soil and the physicochemical properties and soil enzyme activities were determined.The soil NO₃^--N contents were higher by incubating with F1 and F2 groups,and the soil added to F2 group had the highest NO₃^--N content when compared with other groups.The urease activity in the soil incubated by F3 group was highest.The soil alkaline phosphatase activity was higher by incubating with F4 and F5 groups than other groups.It shows that larger cell groups have a greater effect on soil NO₃^--N content,medium-sized cell group have a greater effect on soil urease activity,while smaller cell groups have a stronger effect on soilβ-glucosidase and alkaline phosphatase activity.Further analysis revealed that the effect of each size cell group on soil enzyme activity was significantly higher in maize farm soils than in soybean farm soils.（3）The soil nutrient content and enzyme activity were determined by incubating different mixture of microbial groups in the sterilized soil.We found that the coexistence of different size microbial groups had different effects on the NH₄⁺-N content and enzyme activity in the sterilized soil.Soil NH₄⁺-N content decreased when sterilized soil was added to F5+F4 group in maize fields compared to the two group separately,soilβ-glucosidase activity increased when F3 and F1 group were added together compared to the two group separately,and soil alkaline phosphatase activity increased when F4 and F2 groups were added together compared to the two group separately.Soil urease activity increased when sterilized soil was added together with group F4 and F2 in soybean fields compared to the two group separately.The interaction between smaller cell groups has a greater effect on the NH₄⁺-N content of the soil,and the interaction between larger and smaller cell groups has a greater effect on the enzyme activity of the soil.The interaction between small and large cell groups on soil nutrients and enzymatic activities differed between the different crops grown on the farm.This study investigated the composition and interactions of microbial group of different sizes in maize and soybean cropland soils and their effects on soil nutrients and enzymatic activities,providing a theoretical basis for clarifying the relationship between microbial cell size and its ecological function,and laying the foundation for further clarifying the interactions between soil microorganisms.