Nitrogen is an essential element for growth and development of plants and microorganisms. It was thought that organic N in soil must be mineralized into in-organic form before it is used by microorganisms. However, recent studies showed that small-molecule organic N such as those in amino acids, may be taken up directly as intact molecules or de-aminated extra-cellularly followed by the uptake of ammonium (NH4) absorbed by plants and microorganisms and termed as Direct Rout. The ratio of direct use of organic small molecule N by Soil affects the quantitative characterization of N use efficiency and is one of the new hot spot in the research on N cycling in farmland ecosystem.
Associate Professor ZHANG Lili at Institute of Applied Ecology of Chinese Academy of Sciences recently tested the effect of available C (glucose) and N (ammonium sulfate) on absorption of amino acid by soil microorganism using a laboratory experiment with glycine, NH4 and different levels of glucose.
The results show that the when Nitrogen source (NH4) added alone, amino acid is used mainly by the direct route. When high level carbon source-glucose was also added, initially, the major route of N absorption was direct amino acid absorption because high amount of glucose strongly promoted the growth of the microbial biomass, resulting in increased C and N requirements. With consume of Carbon source, the route gradually shifted from direct uptake to N uptake after extracellular deamination followed by uptake of NH4 or intracellular deamination and excretion of NH4.
This study indicates that amino acids can not only supply N but also supply C for proliferation of soil microorganisms. In the future, more work should focus on the assimilation competition of organic N between plants roots and soil microorganisms.
The study was published in Geoderma.
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