Fate of Free Amino Acids in Paddy and Upland Soils by Using ^<13>C and ^<15>N Tracer Techniques

Abstract

Direct and indirect (=through decomposition) uptakes of free amino acids (FAA) by rice and tomato plants were investigated by using ^<13>C- and ^<15>N-labeled aspartic and glutamic acids, serine, leusine and ammonium as tracers. 1) One week after the surface application of amino acid-N or NH_4-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 applied was 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 around 2 or 3 d and the 1-^<13>C absorption rates of the FAA (RCH(NH_2)^<13>COOH) were high in proportion to the number of carbon atoms of the R side-chain. 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. Percentage of direct-uptake of the FAA in upland soil was much lower than that in the paddy field.