[Effects of water-soluble organic matter and residue of litter on nitrogen transformation in subtropical forest soil.].

An incubation experiment was carried out with the addition of litter filtrate, litter residue and alanine at 25 ℃ for 36 days under 60% and 90%WHC (water holding capacity) conditions. The results showed that alanine was rapidly mineralized in soil, and soil NH-N content significantly increased by 5.4%-44.7% and 16.1%-41.3%, respectively under 60% and 90%WHC conditions compared with the control. The soil net nitrogen mineralization and ammonification rates in the two treatments were also higher than those in the control at the early stage of incubation. However, the soil NH-N content was reduced by the addition of filtrate and residue, and the reduction degree of residue was greater. During the incubation, soil NO-N content showed a linear increasing trend with the incubation time, and it was significantly higher under the 60%WHC condition than that under 90%WHC condition at the end of incubation. The mineralization of soil organic matter was limited by higher soil moisture. Therefore, the soil soluble organic carbon (SOC) content under 90%WHC condition was obviously lower than that under 60%WHC, but nitrous oxide (NO) emission was 1.5-63.0 times higher than that under 60%WHC. Furthermore, NO emission was induced significantly by the addition of litter residue under 60%WHC condition. These results indicated that there were different effects of soluble matter and litter residue on soil nitrogen transformation, and these differences would change dynamically in the decomposition process.