Fine Root Biomass, Morphology, And C And N Concentration Response To Thinning In A Pinus Massoniana Plantation

Fine root, as the key factor of the underground ecological processes of forest, plays asignificant role in carbon and nitrogen cycling in the forest ecosystem. Due to their highheterogeneity of fine root morphology structure, sensitive to environmental change, has differentphysiological function. Thinning changes fine root biomass, morphology and carbon andnitrogen content with different root order, which its effects and mechanism are still not fully clearuntil nowadays. This study investigated the seasonal dynamics of fine root biomass, morphology,carbon and nitrogen concentration in different orders and its soil nitrogen content, water content,temperature and soil enzyme activity response to thinning on a Pinus massoniana (Pinusmassoniana lamb.) plantation of26-year-old after6-year thinning. The main results were asfollows:(1) Thinning, soil depth and season notably impacted on total fine root biomass. The lightthinning increased total fine root biomass in the Spring and Summer, and the middle thinningincreased total fine root biomass in four seasons, while the heavy thinning increased total fineroot biomass in the Spring. Thinning has significantly effects on the lower order root biomass inthe Spring and Summer, while has markedly effects on the higher order root biomass in theAutumn and Winter. The1st-5th fine root biomass and total fine root biomass mainlyconcentrate in the surface soil layer evidently greater than the subsurface, about61.37%-72.38%.The peaks of fine root biomass appeared in the Autumn and the minimum values appear in theSpring at four sites.(2) Thinning dominant significantly increased fine root biomass, diameter, length, SRL,nitrogen and carbon concentration and decreased C:N ratio, but had difference according tothinning intensity, soil depth and season, only for lower order(1st-3rdorder).(3) Each significant effect factor explained proportion no more than10%on the variation offine root biomass in two soil depths. Soil water content was the key impact factor in two soildepth, which can independently interpret the variation of fine root diameter by16.51%and13.87%respectively. The water content and temperature were the key impact factors which canexplain the variation of fine root length in the surface soil layer, by10.95%and10.14%respectively. The soil protease activity and soil catalase activity were the main effect factorswhich can explain the variation of SRL in the surface soil layer, by37.74%and20.37%respectively. The soil protease activity and soil catalase activity were the main effect factors inthe surface soil layer which can explain the variation of fine root nitrogen concentration by54.88%and22.41%respectively, while the soil temperature and soil protease activity were thekey impact factors in the sub-surface which can explain the variation of fine root nitrogenconcentration by19.08%and12.60%respectively. The soil protease activity, temperature andcatalase activity were the key impact factors in the surface soil layer which can explain the variation of fine root carbon concentration by24.41%and19.23%and11.43%respectively,while the soil temperature and water content were the main effect factors in the sub-surface soillayer which can explain the variation of fine root carbon concentration by35.33%and13.72%respectively.In conclusion, Thinning had significant effect on fine root biomass, morphology and carbonand nitrogen concentration, only for lower root. Seasonal dynamics of fine root biomass,morphology, carbon and nitrogen were associated with soil basic physical-chemical character,particularly soil enzyme activities, providing a scientific basis to distinct comprehend theregulated mechanism of fine root structure and function by thinning treatment.