Plastic Responses Of Fine Root Traits To N And P In Ectomycorrhizal And Arbuscular Mycorrhizal Tree Species In An Evergreen Broadleaved Forest

In order to reveal the plasticity response of fine root functional traits of different mycorrhizal types to nutrients,ectomycorrhizal tree species(Castanopsis faberi,Castanopsis carlesll)and endophytic mycorrhiza tree species(Cinnamomum chekiangense,Schima superba)were selected as the research object in the evergreen broad-leaved forest of Wanmulin Nature Reserve,Jianou City,Fujian Province.Control treatments(CT),nitrogen addition treatments(N),and phosphorus addition treatments(P)were set by the root bag method,and each treatment was repeated five times.The fine roots grown in the root bag for half a year,and then root morphological traits(specific root length,specific root area,root tissue density,average diameter),architecture traits(number of branches,branching ratio,branching density,root tip density,colonization rate),and stoichiometric traits(C,N,P,C/N,N/P,C/P)were measured to explore the effect of nutrient availability on the plasticity of fine root traits in different mycorrhizal types.The results show:(1)The increase of N and P availability has different effects on the fine root morphological traits among different tree species,and there is difference even among tree species of the same mycorrhizal type.There is significant negative correlation between the low-order-root specific root length and specific root area and the high-order-root tissue density.There is also significant negative correlation between the low-order-root specific root length and specific root area and the high-order-root tissue density.It indicates that fine roots may have a certain trade-off in N and P nutrient absorption and transportation.(2)With N and P availability increase,the fine root branch number,branching density,and root tip density generally increase.It indicates that the increase of nutrient availability will promote the growth and differentiation of lateral roots,so as to improve the absorption efficiency of nutrients.The root tip density,branching density and colonization rate of different tree species were negatively correlated with the average root diameter and tissue density of the 1st-order root.It indicates that tree species with firstorder root diameter being thick and the construction cost being big requires higher cost,and the fine root branching ability is relatively low.(3)The root N and P concentration of C.faberi,C.carlesll and S.superba decreased with the increase of order,and C concentration,C/N and C/P increased with the increase of order.With N availability increase,low order root N conncentration of C.faberi,C.chekiangense,S.superba increased significantly.With P availability increase,low order root P conncentration of C.chekiangense increased significantly.It indicates that the increase of N and P availability will promote the absorption of N and P,resulting in an increase of N and P conncentration in fine roots.(4)There is a significant positive correlation between the morphological traits of 1st-order root and the plasticity response of nutrient addition.There is also a significant positive correlation between the architecture traits of the 1st-order root and the plasticity response of nutrient addition.After plastic response to N and P nutrients specific root length,specific root area and branch density showed a positive synergistic change.There is a trade-off between root branching ratio and the average diameter in the plastic response to the addition of N and P nutrients.(5)The mycorrhizal type had no significant effect on the nutrient plasticity response of morphological,architectural and stoichiometric traits.There was no significant difference in nutrient response between endophytic and ectomycorrhizal tree species.The stoichiometric traits have a weaker plasticity response to increased nutrient availability.