Comparison Of Variation Patterns Of Fine Root Biomass And Nutrients With Stand Age Between Subtropical Chinese Fir Plantations And Natural Secondary Forests

Fine roots,as the central link of material and energy exchange between plants and soil,play an important role in carbon(C)and nutrient accumulation and cycling in forest ecosystem.Intensive plantations and natural secondary forests are the main ways to restore subtropical forest following human disturbance.Nevertheless,a quantitative evaluation of the dynamics of fine root biomass,necromass,nutrients and C:N:P stoichiometry in plantations and natural secondary forests is lacking.The comparative study of fine root biomass and nutrients between intensive plantations and natural secondary forests is an important way to understand the impact of forest management on belowground ecosystem.Therefore,the study is conducted in natural secondary forests and Chinese fir plantations(5-41 years old)in the Baisha state-owned forest in Fujian Province,and employed primary forest as the reference.Using chronosequence approach to compare the dynamic patterns of fine root biomass and nutrients in Chinese fir plantations and natural secondary forests.The study not only provides theoretical support for optimizing forest management and improving carbon sink function,but also provides basic data for the global fine root ecological database.The main results of this study are as follows:(1)In the 0-60 cm soil layer,the fine root biomass of natural secondary forests and Chinese fir plantations increase and then decline or remain similar with stand age,and reach a peak at 27-31-year age class.The fine root biomass of primary forest is similar to that of natural secondary forests and Chinese fir plantations in 38-41-year age class.In addition,stand age and forest type have a significant interactive effect on fine root necromass.The fine root necromass of Chinese fir plantation increase with stand age.The fine root necromass of primary forest is only similar to that of natural secondary forests in 38-41-year age class.The ratio of necromass and biomass in Chinese fir plantations increase with stand age.(2)Across all age classes(5-41 years),fine root biomass is higher in natural secondary forests than in Chinese fir plantations.Fine root biomass in both Chinese fir plantations and natural secondary forests is mainly concentrated in the 0-20 cm soil layer,and decreases with increasing soil depth.In addition,the fine root necromass in natural secondary forests is significantly lower than that in Chinese fir plantations,except at the early stage of stand development(5-6 years).At all age classes,the fine root necromass and biomass ratio is significantly higher in Chinese fir plantations than in natural secondary forests.(3)Live fine root carbon(C),nitrogen(N),phosphorus(P),potassium(K),calcium(Ca)and magnesium(Mg)concentrations and C:N,C:P and N:P ratio do not vary with stand age in Chinese fir plantations and natural secondary forests.Dead fine root P and Mg concentrations in Chinese fir plantations decrease with stand age,and the P and Mg concentrations are significantly lower in the 19–31-year-old stands.Fine root C,N,P,K,Ca and Mg concentrations of natural secondary forests and Chinese fir plantations in 38-41-year age class are similar to that of primary forests.(4)The P concentration of live fine roots in Chinese fir plantations is higher than that in natural secondary forests,while the Ca concentration is lower than that in natural secondary forests.N,P,and Mg concentrations of dead fine roots in Chinese fir plantations are higher than those in natural secondary forests,while C concentration is lower than that in natural secondary forests.Stand type has no significant effect on the live fine root C:N:P stoichiometry,while the C:N,C:P and N:P ratio of dead fine roots were significantly higher in natural secondary forests than in Chinese fir plantations.The results of this study suggest that the conversion of natural secondary forests to plantations leads to a reduction in fine root biomass across all age classes(5-41 years),which has negative effects on belowground biomass accumulation and nutrient cycling in subtropical forest.Intensive plantations improve the nutrients resorption proficiency of fine root,and result in the decoupling of C:N:P of fine roots in subtropical forests.