Ecological Influencing Mechanism On Phyllostachys Edulis And Broadleaf Trees At Arborous Layer Of Evergreen Broadleaf Forest Due To Phyllostachys Edulis Expansion

Phyllostachys edulis(moso bamboo),a typical clonal bamboo species with strong expansion ability,relies on the powerful rhizome to expand to the adjacent forests.This ecological process has seriously threatened the biomass accumulation,water and soil conservation,biodiversity protection,and other ecological functions of massive evergreen broadleaf forest in subtropical humid areas in China.However,the ecological influencing mechanism on bamboo and evergreen broadleaf forest due to bamboo expansion is still unclear.We set the sampling plots of moso bamboo forests,mixed forests and evergreen broadleaf forests along the direction of bamboo expansion in Yangjifeng National Reserve of Jiangxi Province,and conducted field investigation and sampling.The effects on soil physical and chemical properties and microbial community structure,the plant biomass and relative growth rate(RGR),as well as leaf,stem and fine root functional traits due to bamboo expansion were analyzed.The resource trade-off strategy between bamboo and broadleaf species was explored.Based on the structural equation model(SEM),the regulation mechanism of leaf,stem and root functional traits on the growth of bamboo and broadleaf species was elucidated.The main results showed as follows:(1)Bamboo expansion significantly increased soil ammonium nitrogen(NH₄⁺-N),nitrate nitrogen(NO₃^--N)and available phosphorus concentrations(AP),and thus alleviated soil P limitation to some extent,indicating that bamboo,having a preference for NH₄⁺-N absorption,tended to form a favorable soil nutrient environment for itself.It significantly increased soil bamboo expansion significantly increased the relative abundance of Mortierellomycota,Glomeromycota,Mortierella and Penicillium as well as arbuscular mycorrhizal fungi(AMF)of Pathotroph-saprotroph groups,but decreased Russula,Trichoglossum and Bulleribasidium in mixed forests.It significantly increased fungal Shannon index in mixed forests.However,there was no significant effect on the relative abundance of soil bacterial community,structure and diversity.(2)Bamboo expansion significantly increased leaf carbon concentrations(LCC),leaf nitrogen concentrations(LNC),leaf phosphorus concentrations(LPC),leaf length(LL),leaf saturation vapor pressue deficit(VPD),carboxylation efficiency(CE),stomatal limitation(Ls),water use efficiency(WUE),instantaneous carbon use efficiency(ICUE)and leaf starch contents(SC),but decreased leaf C:P,N:P and leaf thickness(LT),mass-based dark respiration rate(R_mass),area-based dark respiration rate(R_area),transpiration rate(E),stomatal conductance(Gs)and intercellular CO₂ concentrations(Ci)of bamboo.It significantly increased LNC,LPC,mass-based photosynthetic rate(A_mass),area-based photosynthetic rate(A_area),E and Gs,but increased leaf C:N and C:P of broadleaf species in mixed forests.Bamboo expansion significantly increased stem phosphorus concentrations(SPC)and stem SC,but decreased stem C:P,stem wood density(SWD)and stem soluble sugar contents(SSC)of bamboo.It significantly increased stem C:N and mass-based leafing intensity(LIM),but decreased stem nitrogen concentrations(SNC)of broadleaf species in mixed forests.Bamboo expansion significantly increased root carbon concentrations(RCC),root nitrogen concentrations(RNC),root phosphorus concentrations(RPC),C:K,N:K and specific root area(SRA),but decreased root potassium concentrations(RKC),C:N,K:P,root biomass and root tissue density of bamboo.It significantly increased RKC,root K:P and RTD,but dereased RCC,RNC,C:P,N:P,C:K,N:K,specific root length(SRL)and SRA of broadleaf species in mixed forests.(3)LNC,LPC,specific leaf area(SLA),A_mass,R_mass,SNC,stem potassium concentrations(SKC),root biomass(RB),SRL and SRA of bamboo were significantly higher than those of broadleaf species,while leaf C:N,C:P,leaf area(LA),LT,stem diameter(SD),stem length(SL),stem biomass(SB),stem volumn(SV),stem SSC,stem SC and RTD lower in mixed forests,supporting the“phenotypic divergence hypothesis”.(4)Although the number of significant correlated leaf traits of bamboo was lower that in broadleaf species in mixed forests,the number of significant correlated stem and root traits was higher,and the correlation coefficient of bamboo was higher than that of broadleaf species,indicating higher phenotypic integration of bamboo.(5)Bamboo formed trait combinations characterized by higher LNC,LPC,SLA,A_mass,R_mass,RB,SRL and SRA,but lower leaf C:N,C:P,LT,leaf dry matter content(LDMC),RTD,which facilitated bamboo faster capturing and absorption of light,nutrient and water resources.Accordingly,bamboo adopted a“fast investment-return”strategy to compete with broadleaf species,which may be one of the reasons for the successful expansion of bamboo to evergreen broadleaf forests.By contrast,broadleaf species adopted a“slow investment-return”strategy.(6)Bamboo expansion significantly increased average individual growth in diameter at breast height(?D),average individual biomass growth(?M)and average individual biomass relative growth rate(RGR)of bamboo,but decreased?D,average individual biomass in the final period(M₂)??M and RGR of of broadleaf species in mixed forests.The results indicated that the bamboo expansion could promote the bamboo growth and inhibit the growth of broadleaf species in the mixed forests.Bamboo occupied a large niche and had a large overlap degree with woody plants,indicating that bamboo is the main dominant species,occupying a large amount of available resources and having strong adaptability to environment,which led to its strong competitiveness.(7)LNC,SNC and RNC representing resource use had positive effects on bamboo relative growth rate(RGR),while LTD,SWD and RTD representing carbon assimilation had negative effects on RGR of bamboo.Resource use had a significant positive effect on RGR of broadleaf species,characterized by significant positive correlation between LNC and RGR,and negative correlation between SPC,RPC and RGR.LIM and RTD representing carbon assimilation had negative effects on RGR of broadleaf species.The results aims to reveal the ecological influencing mechanism on bamboo and evergreen broadleaf species due to bamboo expansion.It provies scientific reference basis for rational regulation of bamboo expansion and maintaining the stability of the evergreen broadleaf forest ecosystem.