| Phosphorus(P)is one of the essential nutrient elements for plant growth and development.There are various forms of P in soil,but the content of available P that can be absorbed and utilized by plants in subtropical forest soil is low,which leads to P being the main limiting factor for plant growth.Most trees in the forest can form arbuscular mycorrhizal(AM)or ectomycorrhizal(ECM)symbionts with fungi to obtain more nutrients.AM and ECM have different strategies for obtaining soil P,but little is known about how different mycorrhizal tree species regulate and to what extent they affect soil P bioavailability.In this paper,a typical subtropical secondary forest was taken as the research object,and a gradient sample plot of ECM tree species relative abundance was constructed by field mycorrhizal survey method.A new method to simulate the utilization mechanism of plant P-BBP(biologically-based P)method was used to measure the soil bio-available P content in organic layer and mineral layer,and the quantity and quality of litter,soil physical and chemical properties,P cycle function genes and microbial diversity were also measured and analyzed,so as to explore the effects of ECM mycorrhizal tree species relative abundance on soil organisms.The main results are as follows:(1)Except Enzyme-P,the contents of calcium chloride phosphorus(CaCl2-P),citric acid phosphorus(Citric-P)and hydrochloric acid phosphorus(HCl-P)all increased with the increasing of the relative abundance of ECM species,and the contents of Citric-P and HCl-P in ECM-dominated stands were significantly higher than those in AMdominated stands.Total phosphorus(TP)in soil increased with the increasing of relative abundance of ECM species in organic layer,but the trend was opposite in mineral layer.Soil available phosphorus(Olsen-P)increased with the increasing of relative abundance of ECM tree species,and was significantly related to CaCl2-P,Citric-P and HCl-P.The ratio of Citric-P/CaCl2-P,HCl-P/CaCl2-P was greater than 1,while the ratio of Enzyme-P/CaCl2-P was close to 1,whether AM or ECM dominates the stand,which indicated that promoting the dissolution of closed inorganic P by secreting acidic substances instead of enzymatic hydrolysis of organic P was the main strategy for obtaining P from subtropical forest trees.The ratio of HCl-P/Citric-P in AM-dominated forest was higher than that in ECM-dominated forest,which indicated that insufficient secretion of organic acids in AM-dominated forest maked it more difficult to release P from soil matrix.(2)With the increasing of the relative abundance of ECM tree species,the annual litter biomass had no significant change,but the contents of litter P and nitrogen(N)decreased significantly,and the contents of litter C,C/N and C/P increased significantly,indicated that the litter quality of ECM-dominated stands was lower than that of AM.The pH value of soil decreased with the increasing of relative abundance of ECM tree species,which may be due to ECM secreting more low molecular weight organic acids.Due to the influence of litter,organic carbon(SOC)and total nitrogen(TN)in organic layer were significantly higher than those in mineral layer,but there was no significant correlation with the relative abundance of ECM tree species,Soil microbial biomass decreased with the increase of relative abundance of ECM tree species,which showed that AM forest was significantly higher than ECM forest,but there was no significant difference in acid phosphatase(ACP)activity between ECM and AM forest.(3)The dominance of mycorrhiza species affected the abundance of soil P-circulating functional genes,mainly in that the abundance of inorganic P-dissolving functional genes such as gcd and ppa in ECM-dominated stands was significantly higher than that in AM stands.The abundance of ugpA and pstS in phosphorus transport function genes in ECM-dominated stands was significantly higher than that in AM stands.Inorganic phosphorus dissolving function genes phoN,appA,phnG,phnN and organophosphorus mineralization function gene ppx had significant negative correlation with soil pH.(4)The dominant bacterial flora in soil were Actinobacteria,Proteobacteria,Acidobacteria and Chloroflexi,and the bacterial communities were mainly affected by SOC,TN,TP and pH.Ascomycota,Streptophyta and Basidiomycota were the dominant fungi communities,and the relative abundance of Basidiomycota in ECM-dominated stands was significantly higher than that in AM stands.Fungi community was mainly affected by litter C/N ratio and TP.To sum up,the bio-available P in subtropical forest soil was regulated by mycorrhizal tree species,which was helpful to correctly understand the mechanism of multitree species coexistence and productivity maintenance in subtropical forest,and provides scientific basis for tree species selection and proportion allocation of forest management and degraded forest restoration. |
