Seasonal Variations Of Microbial Community Structures And Functions In Cultivated And Natural Restored Mollisols

The black soils in Northeast China are commonly fertile and productive withhigh organic carbon content, which is closely related with soil management practice,climate and soil microorganisms. The climate in Northeast China is characterized bythe extreme annual variation in temperature and precipitation with hot and wet insummer and cold and dry in winter. Consequently, seasonal fluctuations of soiltemperature, soil water content and plant cover are very large for black soils, whichlead to the prediction that soil microbial communities show distinct seasonalvariations in this region. A long term fertilization experimental station which has threefertilizer treatments: no fertilizer (NoF), chemical fertilizers (CF) and chemicalfertilizers plus manure (CFM), and natural restoration (NR) was established in1985.Soil samples (0-20cm depth) were collected on different seasons. Soil dissolvedorganic carbon (DOC) and microbial biomass carbon (MBC) were measured toexplore the seasonal shifts of the active soil organic carbon pool. PCR, DGGE, cloneand sequencing were applied to compare the seasonal variations of microbialcommunities. Microbial metabolic activities (Biolog), soil respiration and soil enzymewere also measured to elucidate how microbial functions changed among differentseasons and treatments. The results were as follows:The value of MBC was highest in spring and the mean value of NR of fivesampling times was higher102%,89%and52%than NoF,CF and CFM, respectively.Soil organic carbon content was higher in samples collected in summer comparedwith those collected in winter. Soil respiration rate from a same treatment but differentseasons was significantly different, and NR was the highest compared with other threecultivated treatments regardless the incubation temperature. NR has the highestactivities of soil catalase, invertase and phosphatase in five sampling times, while thehighest urease activities of NR only appeared in plant growing season. Theapplication of fertilization increased the activities of soil invertase, phosphatase andurease, but the activities of catalase were decreased when only applied chemicalfertilizer. The activities of soil enzymes had obvious seasonal shifts except theactivities of soil invertase in NoF, CF and CFM. The positive relationship betweenMBC and soil enzymes was not obvious in five sampling times.The dominant members of the soil microbial communities were primarilyregulated by land use and also changed seasonally associated with plant growth inblack soils in the region. There was no distinct difference in dominant members ofboth bacterial and fungal communities among different fertilizer treatment plots incultivated black soils. The change of dominant members of fungal communities alongwith land use and season was more obvious than that of bacterial communities,suggesting greater sensitivity of fungi to vegetation, soil disturbance of tillage and soilphysico-chemical properties. Sequence analysis of the DGGE bands revealed thatbacteria belonging to Proteobacteria and Actinobacteria, and fungi of theBasidiomycota and Ascomycota inhabit predominantly in the black soil. Ammonia oxidizing bacteria (AOB) in black soils were distributed in cluster1,cluster2, cluster3, cluster4, cluster7, cluster9and cluster10by phylogeneticanalysis, while Nitrosospira cluster3was dominant in cultivated black soils andNitrosospira cluster1was dominant in NR. The PCoA analysis showed that AOBcommunities of plant growing seasons and no plant growing seasons had highsimilarities, respectively. We found a new cluster (defined as cluster NR in this study)which was not affiliated with any known AOB cluster.Biolog analysis revealed that the microbial metabolic activities (expressed asAWCD,average well color development) of samples from a same sampling time butunder different incubation temperature followed as the order of:28℃＞15℃＞4℃.Samples collected in spring had higher AWCD. For each incubation temperature,AWCD of samples from different sampling time followed as the order of:NR＞CFM＞CF＞NoF. Principal component analysis (28℃,72h) showed that the metabolicactivities of NoF had low similarities with other treatments in four sampling time andmetabolic activities of CF,CFM and NR in plant growing season were obviousdifferent.