Dynamics Of Soil Phosphorus And Its Microbial Mechanisms In Plant Community Of Phosphorus-Enriched Areas Of Central Yunnan,China

The phosphorus(P)-enriched area in central Yunnan is a key prevention and control area for soil P non-point source pollution in southwest China.The joint restoration of plants and microorganisms is one of the most effective prevention and control measures.The core is that in the soil nutrient absorption and utilization process,they form ecological countermeasures to regulate soil element dynamics for better adaptation of the special soil environment in P-enriched areas and reduction of P loss.However,there are few comprehensive reports on the ecological strategies of organisms and their regulation mechanism on soil P in these special P-enriched areas.This study investigated and analyzed the distributional dynamics of soil P in the P-enriched areas of central Yunnan,and found that the biological regulation of P in Pinus yunnanensis forests was prominent in different vegetation types.Taking the biological components directly involved in soil P turnover(aboveground litter,underground root residues,and soil microorganisms)at soil interface in Pinus yunnanensis forests as the research object,the utilization strategies of microbial carbon(C),nitrogen(N),and P and their effects on the seasonal distribution of soil P were analyzed by element stoichiometry,and mechanisms for the dynamic distribution of soil P regulated by the ecological strategies of soil microorganisms were analyzed through metagenomics.The main results are as follows.(1)There were significant differences in soil P dynamics in the P-enriched areas in central Yunnan among different plant communities,such as shrublands,Pinus yunnanensis forests,and mixed broadleaf-conifer forests,and between dry and wet seasons(P<0.05).And the soil P content of Pinus yunnanensis forests was almost always the highest(total phosphorus(TP)11.36～14.98 g/kg,available phosphorus(AP)0.46～1.06 g/kg).The soil AP,TP,and the ratio of AP to TP(AP/TP)in shrublands and mixed broadleaf-conifer forests were all higher in the dry season than in the wet season,while Pinus yunnanensis forests were on the contrary with higher soil P content in the wet season.The findings indicated that the biological turnover degree of soil P turnover in Pinus yunnanensis forests was higher.(2)In Pinus yunnanensis forests,the relationship between soil P dynamic and nutrient utilization by soil microorganisms was closer,rather than by aboveground litter and underground root residues.The dynamic changes of soil P were affected by the changes in soil C and N content.(3)At the horizontal microscale,the AP content(0.32～0.47 g/kg)and AP/TP(about 0.03)in the rhizosphere soil were always lower than those in the non-rhizosphere soil(0.83～1.22 g/kg,0.06～0.09,P<0.05).But the TP content was always maintained at the same high level in both rhizosphere and non-rhizosphere soil(12.88～13.61 g/kg).The contents of soil organic carbon(SOC)and total nitrogen(TN)were higher in the rhizosphere soils,showing an obvious rhizosphere "aggregation effect"(P<0.05).(4)On the vertical scale,the soil layers below 15 or 25 cm were N-limited,and the soil layers above them were still(relatively)P-limited.The soil TP content in the dry season increased with the depth of the soil layer,and the ratio of AP/TP in the surface soil was higher,which was related to the increase of fungal biomass(P<0.05).There was no significant difference in soil P content between soil layers in the wet season(P>0.05),due to the secretion of P and N acquisition enzymes by soil microorganisms in the wet season,which induced the increase of "investment" in the allocation of C acquisition enzymes as well,to make soil C,N,and P nutrients more balanced.These findings indicated that soil microorganisms responded to different nutrient constraints through resource acquisition strategies and high-yield strategies to overcome the constraints of upward P migration to a certain extent when soil nutrients are low.(5)The results of micro-mechanism analysis of soil microbial high-yield strategies showed that when soil nutrient content was low and TP content decreased in the dry season,soil microorganisms allocated more biomass to Paraburkholderia,which was able to cope with refractory organic matter,to increase residues decomposition.In addition,the synergistic effect between different microbial groups(Klebsiella and Nocardia,Paraburkholderia),and with root systems(Bragrhizobium)is also an adaptation strategy of organisms to soil N and P nutrient limitations in the dry season.When the soil nutrient status improved and the TP content increased,there were more soil microbial groups competing for soil C,N,P,and other nutrient resources through the secretion of metabolites such as enzymes and extracellular polymers.At this time,the antagonism between different microbial groups was predominant,but the microbial groups with the ability to decompose C sources(Acidobacteria,Paraburkholderia,Rhodococcus,etc.)also showed a synergistic effect.(6)The results of the molecular mechanism study of soil microbial resource acquisition strategies showed that the abundance of microbial genes involved in C fixation and N metabolism was relatively higher when soil nutrient content was low.For genes encoding proteins involved in soil microbial P turnover,soil microorganisms had a higher potential in P transportation and uptake systems when nutrients were low,and higher gene abundances in phosphate starvation-inducible and key regulatory systems when nutrients were high.However,the abundance of genes related to the organophosphate mineralization process was the highest,no matter how the soil nutrients changed.To sum up,this study focused on analyzing the P dynamics of different plant communities in P-enriched areas,especially the Pinus yunnanensis plant community,and revealed the characteristics of P changes in different seasons,soil horizontal and vertical scales.This study analyzed the contribution of soil microbial high-yield strategies and resource acquisition strategies to soil P distribution patterns,and preliminarily explored the regulatory mechanisms of microbial ecological strategies by species and genes.These findings complement the evidence for a comprehensive understanding of soil microbial ecological functions in P-enriched areas,to provide scientific and data support for bioremediation of P-enriched areas in central Yunnan.