Abundance and composition of CO2 fixating bacteria in relation to long-term fertilization of paddy soils
长期施肥对稻田土壤固碳功能菌群落结构和数量的影响

CO2 fixation is the central mechanism of primary production in almost all ecosystems, and plays a major role in regulating the concentration of atmospheric CO2. Carbon dioxide accounts for about 50% of the current global warming potential. Soil microorganisms that assimilate CO2 are widely distributed, and have a great ability to adapt to environmental extremes, such as within volcanic sediments, lake wetlands and the submarine realm. Microbial CO2 assimilation is of great significance to climate change mitigation and sustainable development for human beings. It has now been well established that atmospheric concentration of CO2 can be reduced significantly by adopting management practices to enhance CO2 sequestration (storage) in cropland soils. Among the approaches for increasing CO2 sequestration of croplands are soil fertilization management practices, such as returning crop residues to the soil, planting temporarily retired land with grass for stabilization, and integrating nutrient management strategies to diversified cropping systems. Paddy soils are distributed widely throughout the world, and generally are known for their production of greenhouse gasses (N2O and CH4). Numerous studies have used molecular techniques to investigate these microbial driving mechanisms. However, few studies have addressed the importance of microbial CO2 fixation processes in paddy soils. Investigation of the impacts of long-term fertilization on the structure and abundance of CO2 assimilating bacteria in paddy soils can provide a theoretical basis for the application of information on fertilization of paddy-rice fields. This type of research also may benefit the reduction of greenhouse gas emissions and increase carbon sequestration. Although carbon fixating microorganisms exhibit a wide range of physiological and ecological traits, most photo- and chemoautotrophic bacteria use ribulose-1,5-biphosphate carboxylase/oxygenase (RubisCO), which catalyzes the first rate-limiting step in the Calvin cycle to incorporate atmospheric CO2. The cbbL gene, which encodes the large subunit of the form I RubisCO is especially useful as a functional marker for significant phylogenetic analyses of CO2 fixating microorganisms in different ecological systems. In this study, soil samples were collected from a long-term fertilization experiment, which included a station that received no fertilization (CK), one treated with chemical fertilization (NPK), and one with NPK plus crop residue return (NPKS). The abundance, diversity, and composition of soil-CO2 fixating bacteria were determined using Polymerase Chain Reaction (PCR), cloning and sequencing, and real-time quantitative PCR of the cbbL gene to explore the effects of long-term fertilization on the structure and abundance of the CO2 fixation bacterial community. Based on sequence libraries of cbbL genes, our results clearly demonstrate that there was a significant response difference in community composition with respect to l