| At present,grazing is the most common form of grassland utilization,but the effects of grazing intensity on soil organic phosphorus mineralization and the microbial mechanism have not been clarified.A long-term grazing experiment was conducted on Stipa breviflora desert steppe in Inner Mongolia.In this study,Bowman-Cole phosphorus grading system was used to compare the differences of organic phosphorus content and mineralization rate in soil under different grazing intensities,and quantitative microbial element cycling(QMEC)technique was used to determine the abundance of microbial phosphorus conversion gene.The response of organic phosphorus to different grazing intensity and its relationship with soil physicochemical properties were clarified,and the response mechanism of soil organophosphorus components and mineralization rate to grazing intensity was revealed.The results show that:(1)Under different grazing intensities,soil total phosphorus(TP)content remained relatively stable,but different organophosphorus components changed obviously.Compared with non-grazing control(CK),the average content of labile organic phosphorus(LOP)increased by 29.2-40.0%,the average content of moderately labile organic phosphorus(MLOP)decreased by 18.6-37.0%,and the content of nonlabile organic phosphorus(NOP)was basically stable.Due to the lack of available phosphorus resources in desert grassland ecosystem,grazing promoted the transformation of soil organophosphates from NOP to MLOP and then to LOP,thus accelerating the mineralization of organophosphates.(2)There were seasonal differences in the effects of grazing intensity on organic phosphate mineralization.Grazing promoted the mineralization of LOP and inhibited the mineralization of MLOP at the beginning of the growing season,and light grazing at the end of the growing season promoted the mineralization of MLOP,while grazing at the beginning and end of the growing season had no significant effect on NOP and its mineralization.(3)Soil physicochemical properties are the main factors affecting the conversion and mineralization rate of soil organic phosphorus components.Soil total carbon content and C/N ratio were positively correlated with soil total phosphorus content,which indicated that phosphorus shortage caused by grazing could be alleviated by increasing carbon substrate concentration in natural grassland ecosystem,so as to maintain sustainable utilization of grassland ecological function.(4)Grazing significantly decreased the absolute abundance of P transforming gene in desert steppe,but with the increase of grazing intensity,the absolute abundance of P transforming gene gradually increased.Grazing affects soil phosphorus cycling mainly by affecting organic phosphorus mineralization,inorganic phosphorus dissolution and hydrolysis processes.Soil temperature,C/N ratio and p H were strongly correlated with the microbial P functional genes: p H was negatively correlated with the absolute abundance of all microbial P functional genes,while soil temperature and C/N ratio were positively correlated with the absolute abundance of all microbial P functional genes,and C/N ratio was significantly positively correlated with the absolute abundance of ppk and ppx genes.(5)There were seasonal differences between the absolute abundance of P conversion functional genes and organic phosphate mineralization.At the beginning of the growing season,the absolute abundances of pqq C and pho D genes were significantly positively correlated with the total organic phosphate mineralization rate and MLOP,while at the end of the growing season,the absolute abundances of bpp and ppx genes were significantly negatively correlated with the total organic phosphate mineralization rate and MLOP mineralization rate.The results of redundancy analysis showed that soil p H value and C/N were the main environmental factors affecting the absolute abundance of P transforming functional genes,and there was a significant correlation between the content of MLOP and its mineralization and the total organic phosphorus mineralization and the abundance of P cycling functional genes.In conclusion,the changes of soil physicochemical properties and microbial phosphorus conversion genes caused by long-term different grazing intensity in desert steppe are the main reasons for regulating the changes of soil organophosphorus and its components.Soil phosphorus mineralization is an important characteristic of organic phosphorus conversion.The effects of grazing intensity on organic phosphorus mineralization are different in seasons,but the driving mechanism is different under different grazing intensity. |
