title: [Effects of water levels and the additions of different nitrogen forms on soil net nitrogen transformation rate and N2O emission in subtropical forest soils].
abstract: An incubation experiment was conducted to investigate the effects of the additions of different nitrogen forms on nitrogen transformation in red soils of subtropical forest under soil moisture conditions with 40%, 70% and 110% of water holding capacity (WHC). The results showed that soil net mineralization and ammonification rates were maximum at 70% WHC and minimum at 40% WHC. Compared with the control, the addition of NO(3-)-N decreased the soil net mineralization and ammonification rates by 56.1% and 43.0% under 70% WHC condition, and decreased by 68.2% and 19.0% under 110% WHC, respectively. However, the proportion of ammonification to mineralization increased at 70% and 110% WHC, which suggested that nitrate addition inhibited the nitrification. With addition of NO(3-)-N at 110% WHC, the net nitrification rate was lowest while N20 emission was highest with the concomitant decrease of nitrate content, indicating that N2O emission was largely derived from denitrification. However, at 40% WHC and 70% WHC, the maximum N20 flux was found at the early stage of incubation. Even with addition of NH(4+)-N and NO(3-)-N, N2O flux did not change much at the latter stage of incubation, indicating that autotrophic nitrification was dominant for N20 production at the early stage of incubation. Under 40% WHC condition, soluble organic carbon increased more and it increased largely with NH(4+)-N addition, which meant NH(4+)-N addition could enhance the mineralization of soil organic matter. Under 40% and 110% WHC conditions, the addition of NH(4+)-N increased significantly the soil soluble organic nitrogen (SON) by 73.6% and 176.6% compared with the control, respectively. A significant increase of 78.7% for SON was only found at 40% WHC under addition of NO(3-)-N compared with the control. These results showed that high soil moisture condition and addition of NH(4+)-N were of benefit to SON formation.
authors.forename: Fen
authors.initials: F
authors.lastname: Ma
authors.forename: Hong-liang
authors.initials: HL
authors.lastname: Ma
authors.forename: Hong
authors.initials: H
authors.lastname: Qiu
authors.forename: Hong-yu
authors.initials: HY
authors.lastname: Yang
mesh_terms: D058440:Denitrification; D065928:Forests; D009566:Nitrates; D058465:Nitrification; D009584:Nitrogen / Q000737:chemistry*; D012987:Soil / Q000737:chemistry*; D014867:Water
chemical_list: D009566:Nitrates; D012987:Soil; D014867:Water; D009584:Nitrogen