Effect Of Interaction Between Nitrogen Deposition And Biochar Addition On Soil N₂O Flux In The Moso Bamboo Plantation

Moso bamboo(Phyllostachys edulis)is a kind of plantation forest widely distributed in the subtropics,covering an area of more than 4 million hectares in China.It accounts for 74%of the national bamboo forest resources and 36%of the world's Moso bamboo forest resources.Due to the fast growth rate of Moso bamboo plant,it has a great advantage in the CO₂ fixation.However,soil N₂O emission fluxes are significantly higher in Moso bamboo plantations compared with broad-leaved evergreen forests.Therefore,development of technologies to reduce soil N₂O emission rate in Moso bamboo plantations is of great scientific significance and practical application.The addition of biochar is one of the effective ways to reduce soil N₂O emissions,but it is not clear whether nitrogen deposition will weaken this effect.Investigation of the effects of nitrogen deposition,biochar addition and their mixed treatment on soil N₂O fluxes in Moso bamboo plantations and the related mechanisms involved is the key to answering this question.In this project,we investigated the effects of nitrogen deposition,biochar addition,and their mixed treatment on soil N₂O fluxes in Moso bamboo plantations through a 12-month location test,and analyzed the major soil factors(soil temperature and moisture content,labile carbon and nitrogen contents,and nitrogen cycle-related enzyme activities)that affect soil N₂O fluxes,and based on this,we discussed the correlation between soil N₂O emission rates and soil factors,under the treatments of control,nitrogen deposition,biochar addition,and their mixed treatment.The results obtained were as follows.(1)Soil N₂O emission rates in Moso bamboo plantations showed a significant seasonal variation in any treatment,with the maximum value occurring in August and the minimum value in January.The annual cumulative soil N₂O emissions were 1.90,1.50,2.18 and 1.70 kg N₂O ha^-1 yr^-1 for the treatments of control,nitrogen deposition,biochar addtion,and a combination of nitrogen deposition and biochar addition,respectively.Biochar addition and its mixed treatment with nitrogen deposition reduced annual cumulative soil N₂O emissions in Moso bamboo plantations by 20.84%and 10.63%,respectively(P<0.05).Neither nitrogen deposition,biochar addition,nor the combination of the two treatments had any significant effect on soil temperature in the Moso bamboo plantaiton.Biochar application increased soil moisture content compared to the control(P<0.05),while neither nitrogen deposition nor the combination of nitrogen depositon and biochar addition had any significant effect on soil water content.Compared to the control,nitrogen deposition,biochar addition and their mixed treatment increased soil WSOC content by 12.31%,2.56%and 13.82%,respectively,and increased soil MBC content by 5.59%,2.82%and 8.15%,respectively.Biochar addition decreased soil NH₄⁺-N and NO₃^--N contents,while nitrogen deposition increased soil NH₄⁺-N and NO₃^--N contents(P<0.05).Both biochar addition and its mixed treatment with nitrogen deposition significantly decreased soil WSON content,whereas nitrogen deposition treatment significantly increased WSON content(P<0.05).In addition,nitrogen deposition,biochar addition,and their mixed treatment increased soil MBN content by 3.12%,13.30%and 14.33%,respectively,compared to the control.(3)Soil urease and protease activities also showed significant seasonal variation characteristics in all treatments.Compared with the control,the biochar addition significantly(P<0.05)decreased soil urease and protease activities in the Moso bamboo plantation by 10.79%and 15.68%,respectively,while the nitrogen deposition treatment significantly(P<0.05)increased the soil urease and protease activities in Moso bamboo plantations by 9.52%and 13.18%,respectively.In addition,the combination treatment of nitrogen deposition and biochar addition had no significant effect on the activities of the aforementioned two enzymes.(4)Soil N₂O fluxes were significantly(P<0.01)correlated with soil temperature,WSOC,nitrate nitrogen content,urease activity,and protease activity,and significantly(P<0.05)correlated with soil ammonium nitrogen content in any of the treatments.Soil N₂O fluxes were significantly(P<0.05)correlated with the MBC content in the control,while no significant correlation was observed for the other treatments.In addition,soil N₂O flux was not significantly correlated with soil moisture content,WSON and MBN in all treatments in Moso bamboo plantations.In summary,the biochar addition significantly reduced soil N₂O emissions from Moso bamboo plantation,the nitrogen deposition treatment significantly increased soil N₂O emissions,and the mixed treatment of nitrogen deposition and biochar addition also significantly reduced soil N₂O emissions from Moso bamboo plantation,indicating that biochar addition still had the effect of reducing soil N₂O emissions in the context of nitrogen deposition.The effect of nitrogen deposition and biochar addition on soil N₂O emissions from Moso bamboo plantation was mainly through the influence of soil NH₄⁺-N,NO₃^--N,WSOC content and soil urease and protease activities.