Effects Of Long-term Warming And Fertilization On Soil Aggregate Stability And Nutrient Accumulation Mechanism In Alpine Meadow

Global warming and nitrogen deposition have increasingly serious impacts on the structure and function of ecosystems.The Qinghai-Tibet Plateau is one of the most sensitive and fragile ecosystems,the mechanism of soil aggregate stability and nutrient accumulation in alpine meadow under global climate change is not yet clear.In this paper,the soil aggregates under long-term warming treatment and fertilization treatment were taken as research objects in Haibei National Field Research Station of Alpine Grassland Ecosystem.The content of soil organic carbon(SOC)? total nitrogen(TN)?total phosphorus(TP)?soil carbon fractions?glomalin-related soil protein(GRSP)of soil aggregates were measured and initially clarified the mechanisms of soil aggregate stability and nutrient accumulation under long-term warming and fertilization treatment.The main conclusions are as follows:(1)Long-term warming treatment reduced the soil aggregate stability of alpine shrubland and had no significant effect on meadow.Under long-term warming treatment,the SOC,TN,oxidizable organic carbon and GRSP contents of alpine meadow decreased,but the inert carbon and TP contents had no significant effect.The decrease of oxidizable organic carbon and GRSP contents was not conducive to the storage of meadow carbon pool.However,Long-term warming treatment promoted the storage of soil carbon in alpine shrubland,which increased the content of SOC and carbon fractions(C1,C3,C4)in shrubland soil aggregates.The warming treatment significantly increased the ratio of GRSP-EE/GRSP-T,and increased the carbon sequestration potential of shrubland soil aggregates.The warming treatment had a significant effect on the distribution of highly active oxidizable carbon in soil aggregates,and the C1 contents in alpine meadow and shrubland microaggregates were significantly higher than that of large aggregates.Soil aggregates affected the distribution of GRSP in alpine meadow and shrubland,and its content increased as aggregate size decreased.Long-term warming treatment did not destroy the stoichiometric balance of meadow,but the ratios of C:N and C:P of shrubland increased significantly.The size of soil aggregates affected the distribution of nutrients and stoichiometric characteristics under warming treatment.The content of SOC,TN and the ratios of C: N,C: P and N: P were significantly higher than that of large aggregates.(2)Soil enzymes(BG,NAG,LAP and AP)activity increased as aggregate size decreased and had little effect by long-term warming treatment in alpine meadow and shrubland.Overall,enzyme activity of alpine meadow was higher than shrubland,which indicated that nutrient cycling in meadow was faster than that in shrubland.Enzyme stoichiometry demonstrated that microbial p-limitation on the Tibetan Plateau is widespread(Vector A>45°),and long-term warming treatment had strengthened the microbial p-limitation of shrubland.At the same time,long-term warming treatment had alleviated C-limitation in the alpine shrubland but not in alpine meadow.Soil microbial C-limitation in microaggregates was stronger than that in large aggregates of alpine shrubland.(3)Long-term fertilization treatment promoted the accumulation of soil aggregate nutrients and had no significant effect on the stability of soil aggregates in alpine meadow.The fertilization treatment increased the contents of C1,C2,GRSP-EE and GRSP-T,which promoted the storage of soil carbon pool.The effect of P addition was the best,with significant differences,and had little effect on the content of C3 and C4.The ratios of GRSP-EE / GRSP-T were between 30%?35% and less affected by fertilization treatment.The size of soil aggregates had a significant effect on the distribution of soil nutrients.The contents of SOC,TN,C1,GRSP-EE,and GRSP-T increased as aggregate size decreased,and the contents of microaggregate were significantly higher those of large aggregate.Long-term fertilization treatment has a greater impact on the stoichiometry of soil aggregates.The addition of N and NP reduced the ratio of C: N,the addition of P and NP significantly reduced the ratios of C: P and N: P.Soil aggregates with different particle sizes have little effect on the soil aggregate stoichiometry.(4)long-term fertilization treatment had a significant effect on soil enzyme activity.The addition of NP and N reduced the activity of LAP and had significant differences in microaggregates.The addition of NP and P significantly reduced the activity of AP in soil aggregates.The activities of NAG and BG were less affected by long-term fertilization.Enzyme stoichiometry showed that long-term fertilization changed the microbial nutrient limitation through the addition of N and P.With the addition of NP,the microbial C-limitation was enhanced,and the addition of N and P had no significant effect.Microbial P-limitation was widespread.The addition of P alleviated the microbial P-limitation,but the P-limitation still existed from the vector A> 45 degrees.The addition of N strengthened the microbial P-limitation,and the addition of NP had no effect.