Factors Affecting the N Uptake Pathway of Soil Microorganisms.

Microorganisms can take up a wide range of mineral and organic nitrogen (N) forms. When organic material is available, soil microorganisms may therefore 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.

Based on a literature review, we concluded that the relative importance of the direct uptake of organic molecules during the decomposition of residue is determined by the availability of NH₄⁺, the source of C, and the availability of N relative to C. However, most of the studies reviewed were conducted with a limited number of cultured microbial species. In an ongoing project we are now testing the effect of these factors on the N uptake pathway of microbial communities in soil.