Effects Of Nitrogen Deposition On Soil Aggregate And Organic Carbon Stability In Subtropical Forest

With the development of social economy,frequent production activities of industry and agriculture,nitrogen?N?deposition has increased widely in China.Soil ecosystem is the largest undertaker of N deposition in terrestrial ecosystem.Soil quality including soil physical,chemical and microbial properties would be changed due to import of exogenous N.Soil organic carbon pool in tropical and subtropical forest as an important composition of global organic carbon pools,its stability is significantly relative to CO₂ concerntration of the world.Soil aggregate stabilitation is counted as an important mechanism of soil organic carbon stability because it could profect organic carbon by insulating microorganism resolving organic carbon to enhance organic carbon stability.Meanwhile,organic carbon could serve as binding agents in the process of soil aggregation.When the N deposition influences soil properties directly or indirectly,also soil aggregates and organic carbon fraction may be changed because of interaction effects among them.However,there is little information about effects of N deposition on soil aggregate stability and interaction between soil aggregate and soil organic carbon.Therefore,we want to determine subtropical forest soil organic carbon fraction,aggregate stability and the interaction between organic carbon and aggregates respons to increasing N deposition.The field experiment?1 year?results showed that organic carbon fraction of bulk soil?0-10 cm?were not significantly influenced by simulating N deposition?p>0.05?,and N deposition declined percentage of labile organic carbon in 0-5 cm bulk soil,which indicated that N deposition may increase potentially soil organic carbon stability in 0-5 cm bulk soil.The field experiment?2 years?results showed that N deposition had no significantly effects on soil organic carbon fraction in water stable aggregates?p>0.05?,which indicated that water stable aggregates might protect soil organic carbon.The stability of large aggregates were not significantly influenced by N deposition?p>0.05?,and the main impacting factors on aggregate stability were soil organic materials,Fe and Al oxides and pH.The incubation experiment?60 days?results showed that N deposition promoted soil organic carbon mineralization,and broken of aggregates could accelerate this effect.At the same time,N deposition could decrease percentage of labile organic carbon and increase percentage of non-labile organic carbon in total organic carbon,which revealed that short-term N deposition positively contribute to soil organic carbon stability,but broken of aggregates would restrain that effect of N deposition on organic carbon stability.Based on the above results,we concluded that short-term N deposition had no significantly effects on soil aggregate stability,and it may increase soil organic carbon stabilization potentially,but broken of aggregate would reduce stability of soil organic carbon.