Dissertation Research: The Functional Significance of Denitrifier Population Diversity to Nitrous Oxide Productionin Terrestrial Ecosystems

本提案将研究环境因子和反硝化细菌多样性对农业和草地生态系统反硝化时空变异的影响。需要解决的具体问题包括：1)在不同氧化亚氮生产潜力的生态系统中，反硝化菌群落组成在多大程度上以及在什么情况下存在差异？2)来自不同生态系统的反硝化菌产生氧化亚氮的速率是否不同？3)氧化亚氮产量的时空变异是否反映了优势反硝化菌种群的差异以及环境控制的差异？这些问题将通过从影响一氧化二氮通量的不同化学条件的生态系统中取样土壤来解决，通过孵育来表征一氧化二氮通量，以及通过反硝化菌分离来表征群落结构。反硝化菌是在厌氧呼吸过程中将植物可获得的氮转化为植物不可获得的气态氧化亚氮的细菌。因此，反硝化剂对土壤肥力和植物生产有直接影响。反硝化也很重要，因为氧化亚氮是一种重要的温室气体，是平流层臭氧衰变的催化剂。影响反硝化过程的环境因素已经得到了研究，但它们的相对重要性和特定反硝化菌种类组成的重要性尚不清楚。本研究将评估环境控制和反硝化菌多样性对氧化亚氮通量的相对贡献。＊＊＊

9311380 Robertson This proposal will examine the effect of environmental factors and diversity of denitrifying bacteria on the spatial and temporal variability of denitrification in agricultural and grassland ecosystems. Specific questions to be addressed include 1) to what extent, and under what circumstances, is denitrifier community composition different among ecosystems with different nitrous oxide production potentials?, 2) do denitrifiers from different ecosystems produce nitrous oxide at different rates?, and 3) does spatial and temporal variability in nitrous oxide production reflect differences in dominant denitrifier populations as well as differences in environmental controls? These questions will be addressed by sampling soil from ecosystems that differ in chemical conditions that affect nitrous oxide flux rates, incubating to characterize nitrous oxide flux rates, and denitrifier isolation to characterize community structure. %%% Denitrifiers are bacteria that, during anaerobic respiration, convert nitrogen from a form available to plants to gaseous nitrous oxide not available to plants. Thus, denitrifiers have a direct impact on soil fertility and plant production. Denitrification also is important because the nitrous oxide is an important greenhouse gas and a catalyst of statospheric ozone decay. Environmental factors affecting denitrification processes have been examined, but their relative importances and the significance of particular denitrifier species composition is not known. This study will all evaluation of the relative contributions of environmental controls and denitrifier diversity to nitrous oxide flux rates. ***