Effect Of Nitrogen Deposition And Biochar Application On The Soil Respiration Component In Moso Bamboo Forests

Moso bamboo(Phyllostachys edulis)is one of the important forest resources in subtropical regions.The area of Moso bamboo forests in China is 4.68×10⁶ hm²,accounting for 72.96%of the area of bamboo forest.Intensive management techniques,mainly including chemical fertilizer application,plowing,and removal of understory vegetation have significantly increased the yields of shoots and timber,but long-term intensive management has caused a significant decrease in soil organic carbon storage and enzyme activity in Moso bamboo forests.The technology of biochar application is considered to be an effective way to reduce soil greenhouse gas emissions.However,the mechanism involved in the effect of biochar application on the soil respiration components of Moso bamboo forests under the background of nitrogen deposition is still unclear.In view of this,a 12-month field manipulation experiment was conducted to investigate the effects of nitrogen deposition,biochar application,and their combination on soil respiration components,temperature and water content,labile organic carbon concentrations and activities of enzymes related to carbon cycling in Moso bamboo forests,and the relationship between soil respiration components and soil environmental factors were discussed.The main findings are as follows:(1)In the treatments of the control(i.e.,no nitrogen deposition and biochar application),nitrogen deposition,biochar application and their combination,soil respiration(R_S),heterotrophic respiration(R_H)and autotrophic respiration(R_A)showed significant seasonal changes.Compared with the control,nitrogen deposition,biochar application and their combination treatments increased the annual cumulative CO₂ emissions of R_S in Moso bamboo forests by 8.84%,4.24%and 14.56%,respectively.Biochar application and its combination treatment with nitrogen deposition significantly reduced the annual cumulative CO₂ emissions of soil R_H(P<0.05),but the nitrogen deposition treatment had no significant effect on it.Compared with the control,nitrogen deposition,biochar application and their combination treatment increased the annual cumulative CO₂ emissions of the soil R_A in Moso bamboo forests by 25.31%,28.81%and 45.88%,respectively.(2)Nitrogen deposition,biochar application and their combination treatments had no significant impact on soil temperature in Moso bamboo forests.Compared with the control,biochar application treatment significantly increased the soil water content(P<0.05),while the nitrogen deposition and its combination treatment with biochar application had no significant impact on it.Compared with the control,nitrogen deposition,biochar application and their combination treatment increased the water-soluble organic carbon(WSOC)concentration by 2.56%,12.31%and 13.82%,respectively,and increased the soil microbial biomass carbon(MBC)concentration by 2.82%,5.59%and 8.15%,respectively.Compared with the control,biochar application treatment reduced the activities of soil invertase and?-glucosidase by 9.46%and 12.27%,respectively,while the nitrogen deposition treatment increased the activities of soil invertase and?-glucosidase by 10.94%and 11.48%,respectively.(3)In the above-mentioned four treatments,there was a significant exponential relationship between the soil respiration components and soil temperature in Moso bamboo forests(P<0.01).Compared with the control,nitrogen deposition and its combination treatment with biochar application significantly increased the temperature sensitivity coefficient(Q₁₀)of soil R_A,while the combination treatment significantly reduced the Q₁₀ value of soil R_H(P<0.05).In any treatment,there is no significant correlation between the rates of soil R_S,R_H and R_A and the soil moisture content in Moso bamboo forests.In any treatment,soil R_S and R_H were significantly correlated with soil WSOC and MBC concentrations,soil invertase and?-glucosidase activities(P<0.05),and soil R_A was significantly correlated with soil?-glucosidase activity(P<0.05).There is a significant correlation between soil R_A and invertase activity in the treatments of control,nitrogen deposition and its combination treatment with biochar application(P<0.05).Only in the combination treatment of nitrogen deposition and biochar application,there is a significant correlation between soil R_A and the soil WSOC and MBC concentrations(P<0.05).In summary,both nitrogen deposition and biochar application treatments significantly increased soil R_A in Moso bamboo forests.Biochar application and its combination treatment with nitrogen deposition significantly reduced soil R_H,and nitrogen deposition had no significant effect on soil R_H,indicating that under the background of nitrogen deposition,the application of biochar still has a significant reduction effect on the CO₂ flux of soil R_H in Moso bamboo forests.