[Effects of L-methionine on nitrification and N2O emission in subtropical forest soil]

The objective of this study was to investigate the influence of L-methionine on nitrification and nitrous oxide emission in a red soil under laboratory incubation experiments. A subtropical broad-leaved forest soil sample was collected from Wanmulin natural reserve in Fujian Province, Southeast China. Five treatments were carried out with three replications, i. e., control (CK), L- methionine addition (M), L-methionine and NH(4+)-N addition (MA), L-methionine and NO(2-)-N addition (MN), L-methionine and glucose addition (MC). The soil moisture was maintained at 60% WHC or 90% WHC. The results indicated that the soil NH(4+)-N content in the M treatment significantly increased by 0.8%-61.3%, while the soil NO(3-)-N content reduced by 13.2%-40.7% compared with CK. Under 60% WHC condition, soil NO(2-)-N content in the MC treatment was higher than in the M treatment, soil NO(3-)-N content in the MA and MN treatments were greater than that in the M treatment, and greater in the MN treatment than in the MA treatment. The soil NO(3-)-N content was lowest in the M treatment after incubation. These results suggested that L-methionine could inhibit nitrosation process of autotrophic nitrification. To some extent, carbon addition as glucose with L-methionine decreased the NH(4+)-N content, inhibited the autotrophic nitrification and their effects were dependent on water level. Under 90% WHC condition, carbon addition improved denitrification more obviously, but the decrease of NO(3-)-N content was not sufficient to prove the inhibition of hetero-nitrification due to carbon addition in the presence of L-methionine. The nitrous oxide emission from soil was increased by L-methionine addition. Compared with 60% WHC condition, the nitrous oxide emission was higher under 90% WHC condition, and the promotion of L-methionine addition on N2O was greater when glucose added.