Fate of free amino acids in paddy and upland soils by using 13C and 15N tracer techniques

摘要

Direct and indirect (through decomposition) uptakes of free amino acids (FAA) by rice and tomato plants were investigated by using 13C- and 15N-labelled aspartic and glutamic acids, serine, leusine and ammonium as tracers. The results showed: (1) one week after the surface application of amino acid-N or NH4-N to paddy soil, the amounts of ammonium remaining in the soil, assimilated ammonium, denitrificated ammonium and amounts taken up by plants were similar; (2) from 5.5 to 7.7% of the FAA appliedwas absorbed directly by rice plants, and from 42.5 to 47.2% of that was indirectly absorbed as ammonium after decomposition. It is suggested that the FAA degraded to ammonium～2 or 3 d and the 1-13C absorption rates of the FAA (RCH(NH2)13COOH) were high in proportion to the number of carbon atoms of the R side-chain; and (3) the absorption rate of N derived from the FAA by tomato plants was lower than that by rice plants, namely, from 0.4 to 1.9% in direct-uptake and from 16.0 to 29.8% in indirect-uptake. The percentage of direct-uptake of the FAA in upland soil was much lower than that in the paddy field.