Nitrogen utilization pathways of soil microorganisms

当有机物质存在时，土壤微生物可以直接吸收简单的有机分子并将剩余的氮以铵（NH4+）的形式释放到土壤中，或者它们可以首先矿化有机氮并以NH4+的形式吸收它。氮素吸收途径对微生物与植物之间的氮素竞争以及作物的氮素营养具有重要意义。建议的研究的目的是获得更好的了解的因素控制的相对重要性的两个氮利用途径的土壤微生物。在第一步中，应开发并测试测定土壤中氨基酸胞外脱氨程度的测定方法。在第二步中，新的测定应结合其他方法，即总氮矿化、氨基酸氮矿化和微生物生物量的天然15 N丰度，在实验室培养中应用，以确定影响两种氮吸收途径相对重要性的因素。第三步，将在实地研究中采用同样的方法，重点是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.