| The natural regeneration of forests plays a pivotal role in preserving the stability and vitality of forest ecosystems,enhancing ecological services such as water and soil conservation,and bolstering carbon sequestration.Nonetheless,the intricate shifts in community structure and ecological functions that occur during this regenerative process,along with their subsequent impacts on habitat conditions,interspecific interactions,and the overall stability and biodiversity of the forest ecosystem,have consistently captivated the attention of forest ecology researchers.One such species of keen interest is Phoebe bournei,a rare and valuable tree species found within the subtropical evergreen broad-leaved forest.Its natural regeneration poses significant challenges,resulting in limited population recovery.To delve deeper into the dynamic growth processes,soil nutrient variations,driving factors,and the intricate plant-soil feedback during the natural regeneration of Phoebe bournei,this study employed a space-for-time methodology and targeted typical Phoebe bournei secondary forests in Anfu County,Ji’an City,Jiangxi Province.Guided by the natural growth timeline of Phoebe bournei,the study comprehensively analyzed stand characteristics,the adaptability of plant leaf functions,litter quantity,and nutrient traits.Additionally,it explored alterations in soil nutrient profiles,microbial structures,and diversity.These meticulous investigations uncovered the natural growth patterns of Phoebe bournei,shedding light on its ecosystem structure,functional processes,and the intricate plantsoil feedback and regulatory mechanisms that underlie its regeneration stages.The key findings of this study are summarized as follows:[Main conclusions to be continued or specified.](1)During natural regeneration,the age structure of Phoebe bournei population showed an inverted "J" type distribution,and the population survival curve tended to Deevey-Ⅱ type,belonging to stable growth population.The niche of Phoebe bournei had the largest width(0.849).The relative abundance,relative frequency,relative dominance,and importance increased with the regeneration process,and the importance values were 7.13%,12.54%,47.43%,and 73.34%,respectively.Leaf length,leaf width,leaf area,specific leaf area,main vein diameter,and primary vein density plasticity index of the leaf were the largest in the regeneration stage Ⅲ and Ⅳ,which proved the trade-off relationship of functional traits of the leaf along the regeneration gradient.The competition between Phoebe bournei and other tree species became more and more dominant.(2)The biomass of litterfall increased with the regeneration stage,and the contents of C,P,and K in litterfall increased with the regeneration stage.The ranges of N and P reabsorption rates between different stages of natural regeneration in Phoebe bournei ranged from 18.07%to 37.36%,and from 66.35%to 78.36%,respectively.The contents of C,P and K in the litter changed with the regeneration stage and generally showed a gradually increasing trend.The soil nutrient quality of Phoebe bournei community in stage Ⅲ is the highest,which proved that of Phoebe bournei community can improve soil nutrient quality through the quantity and quality of the litter.When the Phoebe bournei community population occupied a dominant position in the community,the population entered a high-growth period,which had a significant impact on soil quality.(3)The regeneration process had a significant effect on the structure and diversity of the soil bacterial community and fungal community.Proteobacteria,Acidobacteria,and Actinobacteria were the dominant communities in the regeneration process,while Basidiomycota,Ascomycota,Mortierellomycota,and Cryptomycota were the dominant bacteria in the soil during the regeneration process of Phoebe bournei.With the regeneration processes,the relative abundance of Acidobacteria and Actinobacteria decreased,and the relative abundance of Proteobacteria and increased.The relative abundance of Basidiomycota and Ascomycota showed an increased and decreased trend with the regeneration processes,respectively.Shannon-Winner diversity and richness indices of soil bacteria and fungi showed a decreasing and increasing trend,respectively.(4)The first and second axes of redundancy analysis explained 74.79%and 11.04%variation at the phylum level of soil bacterial community during the regeneration process,respectively,and they jointly explained 85.83%of the total variation.The environmental factors affecting bacterial community variation were leaf N,leaf Mg,and litter K content in sequence.Redundancy analysis explained 56.24%and 33.98%of the variation at the phylum level,and 90.22%of the total variation was explained by both of them.Among them,Ascomycota was positively correlated with soil pH,organic C,total P,and litter Ca,and negatively correlated with other environmental factors.(5)The natural regeneration processes of Phoebe bournei affected soil physical,chemical,and biological characteristics through vegetation type,tree density,and the quantity and quality of the litter.It changed soil microbial food resources and decomposable substrates,by controlling the underground food resources(such as litter biomass,and root biomass)and soil biological community,and implementing microbial ecological niche differentiation.The chemical composition affected the soil microbial community,and litter C:N increased gradually during the regeneration process,while litter N:P decreased.The litter C:N value of Phoebe bournei community promoted the change of soil fungal microbial community by producing a litter with higher C:N.Taken together,during the natural regeneration process,Phoebe bournei trees enter other communities through seed dispersal and take advantage of the number of seedlings,and affect the soil characteristics through the quantity and quality of the litter.The high C:N value of litter inhibits the bacterial community and carries out the regulation of soil physical and chemical properties,soil fertility,and soil nutrient cycle,which continuously occupies and expands the ecological niche,gradually settles down and finally becomes the dominant species.The regeneration of Phoebe bournei breaks through the limitation of soil factors,maintains soil fertility,promotes Phoebe bournei and soil succession,as well as ecosystem stability,and realizes the"plant-soil" mutual feedback and regulation mechanism. |
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