太湖地区长期不同施肥水稻土N2和CO2固定细菌群落结构的特征与差异

土壤N2固定细菌和CO2固定细菌是土壤碳氮循环重要的微生物群落,不同施肥下土壤有机碳积累与这两类微生物群落结构及活性的关系有助于了解施肥对农田碳氮循环的影响特点.本文研究了太湖地区自1987年开始的水稻土长期施肥试验,选取不施肥(NF)、氮磷钾(NPK)肥(CF)、NPK肥与猪粪配施(CFM)和NPK肥与秸秆还田配施(CFS)小区,采集(0-20 cm)表层样本,以nifH和cbbLR基因分别作为N2和CO2固定细菌的指示基因,用PCR-DGGE和荧光定量PCR的方法研究二者的群落结构,并用平板菌落计数法测定土壤自生固氮细菌数量和用乙炔还原法测定土壤固氮酶活性.结果表明,与CF处理相比,CF、CFM和CFS处理下的自生固氮细菌数量分别提高了58％、66％和106％；CF、CFM和CFS处理下的nifH基因丰度分别提高了213％、1079％和344％.CF与CFM处理的土壤固氮酶活性显著高于NF和CFS处理.因此,施肥提高了cbbLR基因的多样性.与NF处理相比,CF、CFM和CFS处理下的cbbLR基因丰度分别提高了465％、1827％和758％.相关性分析表明,土壤自生固氮菌数量与土壤有机碳含量呈显著正相关,cbbLR和nifH基因丰度均与归一化的土壤养分呈极其显著正相关.研究表明,有机/无机肥配施下土壤养分平衡对维持N2和CO2固定细菌较高的丰度具有重要的作用.

Community structure characters and differences of N2-fixing and CO2-fixing bacteria under long-term fertilization in paddy soils of Taihu Lake region,China

Both CO₂-fixing and N₂-fixing bacteria are important microbes involved in soil carbon and nitrogen cycles, respectively. It is helpful for us to know the effect of fertilization on carbon and nitrogen cycles in farmland soils and to analyze the relationship between the soil organic carbon (SOC) and community structures of N2 fixing and CO₂-fixing bacteria. The topsoil (0-20 cm) samples were collected from a paddy field under a long term different fertilization trials initiated in 1987 from Taihu Lake region, China. There were four treatments, no fertilizer application (NF), application of NPK fertilizers only (CF), combined application of NPK fertilizers and pig manure (CFM) and combined application of NPK fertilizers and straw return (CFS). Community structures were analyzed using PCR DGGE and real time PCR with nifH gene and cbbLR gene as indicators of N₂-fixing and CO₂-fixing bacteria, respectively. Cloning forming unit (CFU) of autotrophic azotobacter was evaluated using plating colony counting method. Nitrogenase activity was detected using acetylene reduction method as well. The results show that the abundances of nifH gene in the CF treatment, CFM treatment and CFS treatment are increased by 213%, 1079 % and 344%, respectively compared with the NF treatment, and CFUs of autotrophic azotobacter are increased by 58%, 66% and 106%. Nitrogenase activities in CF and CFM treatments are significantly higher than those in NF and CFS treatments. The diversity of cbbLR gene is increased after the fertilizer application. The abundances of cbbLR gene in the CF treatment, CFM treatment and CFS treatment are increased by 465%, 1827% and 758%, respectively compared with the NF treatment. The statistical analysis reveals there are significant correlations between the two abundances and soil nutrient richness normalized (SNRN) of SOC, total nitrogen (TN) and total phosphorus (TP) and between the CFU of autotrophic azotobacter and SOC. These results indicate that nutrient balances of the combined inorganic/organic fertilization treatments can preserve higher abundances of N₂-fixing and CO₂-fixing bacteria.