Variation in competitive abilities of plants and microbes for specific amino acids

Microbes are assumed to possess strong competitive advantages over plants f or uptake of nutrients from the soil. The finding that non-mycorrhizal plan ts can obtain a significant fraction of their N requirement from soil amino acids contradicts this assumption. The amino acid glycine (Gly) has been u sed as a model amino acid in many recent studies. Our preliminary studies s howed that Gly was a poor substrate for microbial growth compared to other amino acids. We tested the hypothesis that the alpine sedge Kobresia myosur oides competes better for Gly than for other amino acids because of decreas ed microbial demand for this compound. Soil microbial populations that coul d grow using Gly as a sole carbon source were about 5 times lower than thos e that could grow on glutamate (Glu). Gly supported a significantly lower p opulation than any of the ten other amino acids tested except serine. In co ntrast, K. myosuroides took up Gly from hydroponic solution at faster rates than Glu. In plant-soil microcosms, plants competed with soil microbes 3.2 5 times better for Gly than for Glu. We conclude that the low microbial dem and and the rapid plant uptake of Gly relative to other amino acids allow G ly to be an especially important nitrogen source for K. myosuroides.