望天树人工林根际土壤微生物群落随林龄变化特征及其对磷限制的影响

[Objective]The aim of this study was to analyze the current status of rhizosphere soil nutrients and microbial community characteristics in plantations of endangered tree species of Dipterocarpaceae in the subtropics,to clarify the effects of stand age on the structure and function of soil fungal and bacterial communities,and the key role played by rhizosphere microorganisms in the phosphorus(P)conversion process,and to reveal the correlation between microbial communities and P availability and P limitation.[Method]Six stands of pure Parashorea chinensis plantation were collected from rhizosphere soils,and the dynamic transformation characteristics of microbial community diversity and P fraction were analyzed to reveal the interaction between them and the variation characteristics with stand age.[Result](1)The rhizosphere soils of six stands were in a strongly acidic and P-deficient state,with strong P sorption by Fe3+ and high levels of steady-state organic P severely constraining soil P supply;(2)On long time scales,acid phosphatase activity and microbial biomass P were the main drivers of insoluble P activation,and pH,available P,acid phosphatase activity and ammonium nitrogen were key factors driving variation in microbial community diversity;(3)With the increase of forest age,most of the soil physicochemical and nutrient indicators showed a trend of increasing and then decreasing;at the later stage of silviculture,the conversion of other forms of P to available P became increasingly difficult,P availability decreased,and soil fertility began to decline;however,the bacterial community was still able to maintain stable species abundance and diversity,and the evenness of the fungal community tended to increase;(4)the variation of structural composition and functional diversity of the fungal community was more significant than that of bacteria,and fungi were better adapted to the low P environment than bacteria;the growth of dominant fungi was more favorable than that of bacteria,and could better indicate soil P effectiveness and soil quality.[Conclusion]With the increase of stand age,the decrease of acid phosphatase activity in rhizosphere soils moderates the process of mineralization of organic P to bioeffective inorganic P,the conversion of total P to available P gradually weakens,and the content of soil organic matter and available state N,P,and K decreases,leading to nutrient limitation.However,the rhizosphere surroundings of Parashorea chinensis can form acid-tolerant and low P-tolerant microbial communities,thus ensuring higher microbial community abundance and homogeneity,which can maintain P effectiveness and alleviate P limitation to some extent.At the same time,we suggest that an appropriate extension of the fertilization period after the plantation of Parashorea chinensis will be beneficial to maintain the soil P supply capacity and ensure the normal growth and development of beneficial microorganisms and trees.This study helps to improve our understanding of the mechanisms of soil maintenance in plantations in acidic low P red soil areas,and may also provide scientific reference for soil suitability,fertilization duration and maintenance of rhizosphere microbial community structure during the relocation of endangered plants for conservation and plantation,etc.