Microorganisms In Carbon-nitrogen Transformation And Its Functions In Subtropical Soils Of China

The subtropical region of China, cover about21%of the country’s land surface, is the main area of agricultural production in our country. Soils in this region, characterized with low pH, highly weathered, high oxidation potential, play a unique role in the world. Soil carbon and nitrogen biogeochemical cycles in this region are closely related to environmental change, agricultural production, etc. Therefore, it will be instructive to understand microbial characteristics and their functions related to carbon-nitrogen transformations for grasping the laws of carbon and nitrogen biogeochemical cycles and developing sustainable green agricultural production.Typical rice-growing area in subtropical region (Wuhan, Hubei province, China) was selected to be the study site. Static closed chamber technique was employed to analyze the effect of planting transgenic Bt rice on greenhouse gases (GHQ such as CH4, CO2and N2O) emission from paddy soil under both field and greenhouse conditions. Modern molecular ecology methods were employed to investigate the effect of planting transgenic Bt rice on functional microorganisms related to GHGs emission. DNA-based stable isotope probing (DNA-SIP) method was employed to investigate the effect of planting transgenic Bt rice on functionally "active" methanogenic archaea. The objective of this study was to understand the microbial characteristics of carbon transformation and the functions in subtropical region. The results are as follows:(1) Under both field and greenhouse conditions, planting transgenic Bt rice significantly and persistently reduced the CH4, N2O and CO2emission. Planting transgenic Bt rice did some significant and negative effects on community abundances and composition (characterized by Shannon-Weuner diversity index) of rhizospheric methanogenic archaea and methanotrophic bacteria. The community abundances of total bacteria in Bt rice rhizosphere at SI and S2stages were significantly lower than Ck rice rhizosphere (p<0.05), but these significant differences disappeared at following stages. The community abundance of total archaea in Bt rice rhizosphere at S3stage was significantly lower than Ck rice rhizosphere (p<0.05), but these significant differences disappeared at following stages. Regression analysis shown that the CH4emission flux significantly increased with the increasing of methanogenic archaeal abundance (R2=0.839, p<0.001), and the N2O emission flux significantly increased with the increasing of N2O production microorganism abundance (R2=0.564, p<0.05). We inferred that the lower root exudates contents, plant biomass and functional microorganism abudance and the higher soil redox potential of Bt rice were the key reasons resulting in the lower greenhouse gases emission fluxes.(2) Results of SIP-DNA indicated that planting transgenic Bt rice significantly reduced the community abundance of functionally "active" methanogenic archaea, but did not affect the community composition. The populations of functional "active" methanogenic archaea in Bt and Ck rice rhizosphere were Rice cluster-I (RC-I), Methanosaetaceae, Methanosarcinaceae and Methanobacteriacea. RC-I is represented by the most species, accounting for60%～66.7%of total functional "active" methanogenic archaeal populations.Typical forest soils (Altingia gralilipes, ALG; Cinnamomum chekiangense, CIC) and changed agriculture soils (Cunninghamia lanceolata, CUL; Orange orchard, ORG) in subtropical region were selected to be another study site. Modern molecular ecology methods were employed to investigate the effect of forest conversion to agriculture on ammonia oxidizers and their contributions to autotrophic ammonia oxidation process. The objective of this study was to understand the microbial characteristics of nitrogen transformation and the functions in subtropical region. The results are as follows:(1) People use and fertilization significantly increased soil potential ammonia oxidation in this region. Forest conversion to agriculture significantly increased ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) community abundances, and changed AOA and AOB community structures. The relative contributions of AOA and AOB to autotrophic ammonia oxidation process were also changed after the land-use conversion. Forest conversion to agriculture significantly changed the community compositions of AOA and AOB. The AOA populations (A7-A10), belong to Group1.la-associated lineage, could not be detected after fertilizing. The AOB population (B6), belong to Cluster3a lineage, could not be detected after fertilizing.(2) The Urea addition significantly increased the AOA abundance in natural forests (ALG and CIC), significantly promoted the AOA and AOB abundances in unfertilized plantation soil (CUL), but had no significant effect on the AOB abundance in natural forests and the AOA and AOB abundances in fertilized soil (ORG). The Urea addition significantly changed the community compositions of AOA, but had no significant effect on the community compositions of AOB. We inferred that AOA may dominate the autotrophic ammonia oxidation process in natural forests (ALG and CIC), whereas both AOA and AOB may conduct autotrophic ammonia oxidation in agriculture soils (CUL and ORG). We supported that forest conversion to agriculture significantly changed the relative contributions of AOA and AOB to autotrophic ammonia oxidation, but the relative contribution ratio in these soils still remained unknown.