| An simulation experiment of warming and nitrogen deposition was conducted to research the effect of climate change on seasonal soil nitrogen mineralization dynamics.Seasonal nitrogen mineralization rate was measured by PVC tube closed-top in situ incubation method.Soil available nitrogen was determined by using ion-exchange resin bags method.We also conducted an indoor experiment with warming and nitrogen deposition to study soil nitrogen mineralization and soil N2O emission.The results are as follows:Warming and nitrogen deposition have significantly contributed to the soil nitrogen mineralization process(P<0.05),but the present laws are inconsistent among different seasons and varies from season to season.Warming in summer have no significant influence on soil nitrogen mineralization rate(P>0.05),the other three seasons are increasing significantly(P<0.05).After warming treatment,the average soil nitrogen mineralization rate was 9.21 ±0.14 mg·kg-1·30 d-1,compared with control treatment,increased by 107%.Nitrogen deposition improved annual soil nitrogen mineralization rate,but show limit in summer,promote in spring and autumn and no significant influence in winter.Average nitrogen mineralization rate of low and high nitrogen depositon were 8.54 ± 0.88 mg·kg-1·30d-1,7.69±0.61 mg·kg-1·30 d-1,1.92 and 1.92 times that of control treatment,respectively.Seasonal trends of warming × nitrogen deposition treatment is similar with warming alone.Except summer,nitrogen mineralization rate in the other three seasons were significantly increased.Average nitrogen mineralization rate of warming X low nitrogen and warming×high nitrogen were 6.00± 0.27 mg·kg-1.30 d-1 and 10.38 ±1.81 mg·kg-1·30 d-1,increased by 35%and 134%,respectively.Soil nitrogen mineralization rate is significantly negative correlation with precipitation(R2=0.18,P=0.18),and temperature have no significant correlation(R2=0.01,P=0.01).Throughout the study period,warming,nitrogen deposition and their interaction significantly improved soil available nitrogen content.Nitrate is the main form of soil available nitrogen.Whether nitrogen deposition alone or combined with warming,soil available nitrogen increased with nitrogen deposition level.Warming×nitrogen deposition has a greater effect than any single factor.Soil average available nitrogen content after warming,low nitrogen,high nitrogen,warming× low nitrogen and warming×nitrogen treatment,nitrogen were 30.69±3.50 μg·d-1.g-1 dry resin,37.51±1.9μg·d-1·g-1 dry resin,78.43 ± 11.10μg·d-1.g-1 dry resin,57.08±3.72 μg·d-1·g-1 dry resin and 152.92±9.96μg·d-1g-1dry resin respectively,3.42,4.18,8.75,6.36 and 17 times higher than that of control treatment.Available nitrogen has a significantly negative correlation with temperature(R2=0.16,P=0.16),no significant correlation with precipitation(R2=0.02,P=0.2),and positive correlation with nitrogen mineralization rate but failed to reach significance level(R2=0.01,P=0.67).Early in the indoor incubation experiment,a markable increase in soil nitrogen mineralization rate of warming was found and started to decline from the peak.It is slightly higher than the control treatment at the end of incubation.Nitrogen deposition treatment reached maximum in the beginning and declined all the way.In the end,low nitrogen had a slight promotion to nitrogen mineralization,while high nitrogen showed limitation.Warming×nitrogen deposition on soil nitrogen mineralization had a similar trend with nitrogen deposition alone:high in the beginning and declined to the same level of control treatment.Results of soil N2O emission showed that warming and nitrogen deposition restrain soil N2O emission,soil N2O emission rate is lower than control treatments all throughout the incubation period.Soil N2O emission rate of nitrogen deposition treatment ranged around control treatment.N2O emission rate of warming ×nitrogen deposition were lower than control treatment in the early and middle of the experiment,higher in the end.During the experiment,whether warming and nitrogen deposition alone or not,N2O cumulative emissions were lower than control,treatment.warming and nitrogen deposition restrained soil N2O emission.Because warming and nitrogen deposition reduced soil pH,thus suppressing ammonium carboxyl to nitrite,which reduces soil N2O emission. |
PDF Full Text Request