Effect Of Fertilization On Soil Organic Carbon Components And Decomposition Dynamic In Alpine Meadows On The Qinghai-Tibetan Plateau

Human activities promote the increasing of atmospheric nitrogen?N?deposition.It will change the nutrient inputs such as N and phosphorus?P?and affect soil organic carbon?SOC?storage and soil functioning as C pool in ecosystems.Soil aggregates affect the cycle and turnover of SOC.Microbial community can affect the SOC decomposition through heterotrophic respiration and soil enzymes.However,how N and P input affect grassland soils'functioning as C pool and the mechanisms remain inconsistent.In this paper,we studied the effect of fertilization?N,P,and NP?on turnover of particulate organic carbon?POC?and enzymes activities in soil aggregates.We also investigated the relationships between soil microbial respiration,the size of active and stable C pool with POC and soil enzymes through incubation experiment and using the double exponential model.It will help us to understand the mechanism of organic C sequestration and provide a theoretical basis for the ecological restoration and maintaining soil ecological functioning as C pool of alpine meadow ecosystems in this and other regions.The results showed that:1.N-alone fertilization significantly reduced the proportion of large-macroaggregate?>2mm??-11.83%?.2.N-alone fertilization significantly increased the coarse-POM in large-macroaggregate and the fine-POM in microaggregate while decreased the MOM.3.N-alone and NP fertilization significantly increased the coarse-POC and N-alone significantly increased the cPOC/fPOC?+18%?and POC/MOC?+39%?in large-macroaggregate,N-alone significantly increased the fine-POC in microaggregate.4.N-alone fertilization significantly decreased the activities of peroxidase?-58.22%?,phenoloxidase?-45.05%?and sucrase?-34%?in large-macroaggregate.NP fertilization significantly decreased the sucrase activities?-34.51%?.5.N-alone and NP fertilization significantly decreased the cumulative C mineralization(about-450 mg kg^-1).P-alone fertilization increased the size of soil active C pool(+0.392 g kg^-1)and decreased the size of stable C pool(-2.812 g kg^-1)significantly.Phenoloxidase in the smallmacroaggregate was mainly responsible for the changes in soil active and stable C pool.6.In the largemacroaggregate,POC was negatively related to sucrase,peroxidase and phenoloxidase.POC was positively related to phenoloxidase and cellulase in the smallmacroaggregate.Taken together,these findings suggested that:1.Fertilization destroyed the stability of soil largemacroaggregates,especially N-alone fertilization decreased enzymes activities in macroaggregate,enhanced the accumulation of POC and the turnover of C.This went against aggregates formation and SOC sequestration in alpine meadows.2.Fertilization decreased microbial respiration,which would slow the nutrition turnover in ecosystems and restrict plant growth.In the long run,it would reduce the C input to soil and would have negative effects on the functioning as C pool in alpine meadows.3.Fertilization affected soil active and stable C pool;SOC shifted from the stable state to active state.This would go against SOC sequestration in alpine meadows.