Influence Of Long-term Grazing On Soil Organic Phosphorus Turnover In Stipa Breviflora Desert Steppe

Due to phosphorus limitation in terrestrial ecosystems globally,phosphorus turnover is critical for maintaining primary productivity in grassland ecosystems.The phosphorus turnover is affected by anthropogenic disturbances(such as grazing).Grazing-induced plant characteristics,soil properties,and microbial communities variations will modify organic phosphorus turnover in grassland ecosystems.In the barren steppe,grazing could make the demand and supply of phosphorus conflict even worse.Therefore,it is important to investigate how phosphorus turnover responds to grazing,and the mechanisms of its regulation by plants,soil,and microorganisms in order to maintain phosphorus supply capacity and predict its availability in desert steppe.This research was carried out on a long-term grazing experimental platform to investigate the effects of grazing on the organic phosphorus turnover in desert steppe.Soil organic phosphorus pool content and composition,organic phosphorus mineralization and transformation rate,and plant-derived phosphorus input were examined to explore the underlying mechanisms.The main results are summarized as follows:1.Heavy grazing reduced the labile,moderately labile organophosphorus and promoted the accumulation of stable organophosphorus.The response of organic phosphorus fraction to environmental changes was variable,in which labile organophosphorus was significantly influenced by pho D-harboring bacteria,stable organophosphorus was unaffected,and moderately labile organophosphorus was co-regulated by soil,plant and pho D-harboring bacteria.The enhanced moderately labile organophosphorus was significantly correlated with increased aboveground biomass,soil temperature and labile organophosphorus,and also associated with decreased belowground biomass and pho D-harboring bacteria diversity.2.Both light and heavy grazing increased the soil organophosphorus mineralization rate as well as the labile organophosphorus transformation rate.Light grazing promoted the moderately labile and stable organophosphorus transformation rate.The soil phosphorus pool influenced phosphorus transformation more than expected,with increased organic phosphorus fraction promoting the corresponding transformation rate and the organic phosphorus mineralization rate.In addition,the labile organophosphorus transformation rate was inhibited by higher above-and below-ground biomass.The relative abundance of pho D-harboring bacteria was significantly correlated with organophosphorus transformation rate.Several rare taxa of pho D-harboring bacteria contributed significantly to soil organic phosphorus processes and transformation.3.The total phosphorus concentration in senescent leaves of Cleistogenes songorica increased with moderate and heavy grazing,while Stipa breviflora showed an inconsistent pattern due to interspecific differences and water limitation.Phosphorus content in senescent leaves is linked to soil moisture,soil nutrient,and aboveground biomass with dissimilar patterns due to species-specific variability.We found moderate grazing significantly elevated phosphorus resorption in both species,but heavy grazing significantly decreased that in Cleistogenes songorica.Phosphorus resorption was enhanced by lower soil moisture and higher phosphorus content in green leaf.In conclusion,grazing significantly influences the soil organic phosphorus pool,organic phosphorus mineralization and transformation in desert steppe,especially heavy grazing will improve the stability of the organic phosphorus pool.Both light and heavy grazing promoted soil organic phosphorus mineralization rate and labile organic phosphorus transformation rate,which in turn improved the soil phosphorus supply capacity.The organophosphorus fraction content was combined effected of plants,soil and microorganism,in particular moderately labile organophosphorus.The organophosphorus mineralization and transformation are largely determined by the content and composition of soil phosphorus pool,which are regulated by plants and microorganisms as well.We investigated the effect of grazing on soil phosphorus turnover in desert steppe ecosystems based on soil organic phosphorus pools,the organic phosphorus mineralization and transformation rate.The mechanisms of phosphorus turnover by soil,plants and related microorganisms were elucidated,providing an important scientific basis for the sustainable use and maintenance of phosphorus effectiveness in desert steppe ecosystems.