Masson Pine Plantation C, N, P Stoichiometry, Microbial Community Characteristics And Their Correlation

Pinus massoniana is a pioneer tree species for afforestation and main timber tree species in South China,which plays an extremely important role in China's forestry production and forest ecosystem.For a long time,the productivity and economic value of P.massoniana plantations have attracted much attention.However,the dynamic process of P.massoniana growth and development,the utilization strategy of tree nutrient elements and their relationship are not fully clear.Therfore,in order to reveal the N and P nutrient utilization characteristics,cycling pattern and their relationship with tree growth rate and microbial community in the P.massoniana plantation,so as to provide scientific guidance for rational fertilization of P.massoniana plantation,promoting tree growth,development and management.In this study,young(10-year-old),middle-aged(20-year-old),near-mature(30-year-old)and mature(36-year-old)P.massoniana plantations were selected as the research objects in Meng Guan forest farm,Guizhou province.Based on the theories of ecological stoichiometry and growth rate hypothesis,to explore the changes and relationships among them of tree growth rate and various organs,litter,soil carbon(C),nitrogen(N),phosphorus(P)stoichiometry and microbial community characteristics of P.massoniana at different growth stages.The main results indicated that:(1)The contents of total organic carbon(TOC),total nitrogen(TN),and total phosphorus(TP)and stoichiometric ratio in different organs of P.massoniana showed different trends with the increase of stand age,and there were N and P limitation at different developmental stages.The TOC content of each organ changed little with the increase of stand age,TN content of leaf tended to increase,TN content of stem and root decreased first and then increased;TP content of leaf and root increased first and then decreased,and the TP content of stem had no significant difference;The C/N ratio of leaf tended to decrease with the increase of stand age,while the C/P ratio first decreased and then increased,indicating that the N utilization rate decreased while the P utilization rate increased with the increase of stand age;N/P ratio of leaf in young and middle-aged forests were 12.47 and 11.05,respectively,showing N limitation,while those in near-mature and mature forests were 17.02 and 18.46,respectively,showing P limitation.The relative growth rate of P.massoniana was significantly positively correlated with the TP content and C/N ratio of each organ,while negatively correlated with the C/P and N/P ratios,which accords with the growth rate hypothesis.(2)The TOC,TN,and TP contents and stoichiometric ratio and N,P nutrient resorption rate of P.massoniana changed significantly with the increase of stand age.The TOC and TN contents,C/P and N/P ratios of litter increased with the increase of stand age,while the TP content and C/N ratio decreased;The N reabsorption rate increased first and then decreased with the increase of stand age,and the correlation with N/P ratio of leaf was not significant;P reabsorption rate in near-mature and mature forest was significantly higher than that in young and middle-aged forest,and was significantly correlated with TP content,N/P ratio of leaf and litter.(3)The TOC,TN,and TP contents and stoichiometric ratio,available nutrients,and p H value showed different trends in different soil layers with the increase of stand age,and were significantly correlated with microbial Shannon-Wiener index and community composition.Firstly,soil TOC and TN contents decreased in each stand age with the increase of soil depth,but the change of TP content was generally small;soil TOC and TN contents decreased first and then increased with the increase of stand age,while TP content increased first and then decreased;soil TOC and TN contents were the main factors that regulate soil stoichiometric ratio,and AP content could indirectly affect soil stoichiometric ratio by affecting TOC and TN contents.Secondly,the bacterial Shannon-Wiener index tended to decrease with the increase of stand age,while the fungal Shannon-Wiener index decreased first and then increased,and they were significantly positively correlated with soil AP content.Furthermore,Acidobacteria was the most abundant bacterial community,followed by Actinobacteria and Proteobacteria;Basidiomycota was the most abundant fungal community,followed by Ascomycota and Eukaryota-unclassified,and soil TOC,AP,and C/P ratio were the main influencing factors of the microbial community,and TOC is the most critical factor.(4)There was a significant correlation between TOC,TN and TP stoichiometry in different organs,litter,and soil of P.massoniana and microbial communities.First of all,the stoichiometry in leaf,litter of P.massoniana,and soil were significantly correlated with each other,and the stoichiometry of stem and root were significantly correlated with soil.Secondly,the stoichiometry of soil,root,and litter were also significantly correlated with microbial Shannon-Wiener index.Moreover,redundancy analysis showed that the interpretation rate of soil stoichiometry(45.04%)to microbial community was higher than root(19.95%)and litter(31.62%)stoichiometry.In conclusion,the young and middle-aged forest stage of P.massoniana showed N limitation,and the near-mature and mature forest stage showed P limitation.The N utilization rate decreases and the P utilization rate increases with the increase of stand age.This is a survival strategy for P.massoniana to adapt to poor nutrient status;Soil AP was the main factor affecting the diversity of bacterial and fungal communities,while TOC was the key factor affecting the microbial community structure;There was a significant correlation between TOC,TN and TP stoichiometry in different organs,litter,and soil of P.massoniana and microbial communities,and the influence of soil stoichiometry on microbial communities was greater than that of root and litter.