Distribution Characteristics Of Soil Organic Phosphorus Fractions And Their Regulating Factors In Pinus Taiwanensis Forests At Different Elevations In Wuyi Mountain

Understanding the fate and abundance of soil organic phosphorus is a prerequisite for predicting the effects of climate change on phosphorus dynamics and availability in subtropical forests.At present,there is no uniform theory on the distribution pattern of soil organic phosphorus fractions along the elevational gradient,which is mainly due to the neglect of the fact that the response of soil organic phosphorus fractions to elevation is more complicated due to the change of vegetation type,and it is difficult to accurately assess the dynamics of organic phosphorus fractions and its key regulating factors.In this study,the distribution characteristics of basic soil properties,organic phosphorus fractions and microbial properties in summer and winter at different elevational gradients(1200 m,1400 m,1600 m,1800 m and 2000 m)were investigated in a Pinus taiwanensis forest in Wuyi Mountain,and the following conclusions were mainly drawn.(1)The content of soil organic phosphorus fractions in Pinus taiwanensis forests differed significantly between different elevations.The content of organic phosphorus fractions at lower elevations(1200 m,1400 m,1600 m)was significantly lower than that at higher elevations(1800 m,2000 m),indicating that soil phosphorus availability and supply capacity were lower at lower elevations.In addition,there were some seasonal differences in soil organic phosphorus fractions at different elevations,with the contents of labile organic phosphorus and moderately labile organic phosphorus being higher in winter than in summer,while the opposite trend was observed for highly resistant organic phosphorus,indicating that seasonal changes in phosphorus demand by plants and microorganisms would affect the contents of organic phosphorus fractions.(2)Soil microbial biomass carbon,nitrogen,phosphorus(MBC,MBN,MBP)and its stoichiometry and phosphatase activity were significantly different between elevations.Among them,MBP was significantly lower at lower elevations than at higher elevations,whereas MBC:MBP,MBN:MBP,acid phosphate monoesterase(Ac P),alkaline phosphate monoesterase(ALP),and acid phosphate diasterase(PD)activities,as well as Ac P:MBC,ALP:MBC,and PD:MBC showed opposite trends,indicating that soil microorganisms at lower elevations may have greater competition for phosphorus.Microorganisms allocate more energy to phosphatase secretion to promote organic phosphorus mineralization rather than investing in microbial biomass growth to obtain available phosphorus.(3)The diversity,structure and species composition of soil bacterial and fungal communities differed significantly between elevations,and the effects of elevations on bacterial and fungal community structure was greater than seasonal effects.PICRUSt functional prediction analysis showed significant differences in the abundance of Ac P,ALP,and PD from soil bacterial and fungal sources at different elevations,and the trends of Ac P,ALP,and PD activities in the measured soils were basically consistent,further verifying the higher phosphorus demand of soil microorganisms(dominated by bacteria and fungi)at lower elevations,indicating that bacteria and fungi play an important role in the soil organic phosphorus cycle through the secretion of phosphatase.(4)The analysis revealed that soil total phosphorus(TP),soil temperature(ST)and SM were key abiotic factors affecting soil organic phosphorus fractions along the elevational gradients.MBP and Ac P were key microbial factors influencing the variation of soil organic phosphorus along the elevation gradient,and that Bradyrhizobium was a key microbial taxa influencing the organic phosphorus fractions,suggesting that they have an important role in driving the soil phosphorus cycle and the transformation of the organic phosphorus fractions.In summary,the variation of soil organic phosphorus fractions in Pinus taiwanensis forests at different elevations in Wuyi Mountain is the result of a combination of abiotic and biotic processes.The results of this study can help improve the scientific basis for maintaining soil nutrient cycling and woodland management in subtropical mountains,and provide theoretical support for accurately assessing the biogeochemical cycling of soil organic phosphorus using a process-based Earth system model.