Nitrogen utilization pathways of soil microorganisms

当有机物质可用时，土壤微生物可以直接吸收简单的有机分子，将多余的氮(N)以铵（NH4+）的形式释放到土壤中，也可以先矿化有机氮，以铵（NH4+）的形式吸收。氮的吸收途径对微生物和植物之间对氮的竞争有影响，因此对作物的氮营养有影响。本研究的目的是为了更好地了解控制土壤微生物对两种氮素利用途径相对重要性的因素。在第一步中，应开发和测试一种测定土壤中氨基酸细胞外脱胺程度的方法。第二步，将新方法与其他方法（即总氮矿化、氨基酸氮矿化和微生物生物量天然15N丰度）结合在实验室培养中，确定影响两种氮吸收途径相对重要性的因素。在第三步中，同样的方法应应用于实地研究，该研究将侧重于施肥管理的时间效应，包括有机和矿物肥料，以及与作物的相互作用。

When organic material is available, soil microorganisms may either take up simple organic molecules directly and release the surplus nitrogen (N) into the soil in the form of ammonium (NH4+), or they may mineralize organic N first and take it up in the form of NH4+. The route of N uptake has implications for the competition for N between microorganisms and plants and therefore for the N nutrition of crops. The objective of the proposed study is to gain a better understanding of the factors controlling the relative importance of the two N utilization routes by soil microorganisms. In a first step, an assay to determine the extent of the extracellular deamination of amino acids in soil shall be developed and tested. In a second step, the new assay shall be applied in laboratory incubations in combination with other methods, namely gross N mineralization, mineralization of amino acid-N, and natural 15N abundance of the microbial biomass, to determine the factors affecting the relative importance of the two N uptake routes. In a third step, the same methods shall be applied in a field study, which will focus of the temporal effects of fertilization management, including organic and mineral fertilizers, and the interactions with crops.