Root Decomposition And Humification In The Western Sichuan:the Effects Of Forest Gap And Diameter Classes

Forest gap is the main way of forest natural regeneration and the redistribution of forest gap on sunlight,temperate and precipitation may alter the decomposition environments of biotic and abiotic,and then manipulate the root decomposition processes in the gaps.Root is one of the most important part of forest litter composition.The decomposition of root litter is crucial to soil carbon and nutrient cycling in terrestrial ecosystems.Most of the studies interested in unraveling the decomposition patterns of fine root.However,the decomposition dynamic of coarse roots and its controls are not as well understand as those on fine roots.Thus,a two-year field experiment was conducted to examine the mass loss,element releasing and humification dynamics of three root diameter classes(0-2 mm,2-5 mm and 5-10 mm)in two needle species(Picea asperata,Abies faxoniana)using a litter-bag method on forest gap of the subalpine forest of western Sichuan.The main results are as follows:1.Root mass remaining was affected by tree species,diameter classes and samplingdates.Root mass loss rates were decreased with increasing diameter roots,androot mass loss in the winter account for 56.18%-80.45% of two years.Meanwhile,the root decomposition rates were also effected by forest gap,root decompositionconstant that k value ranged from 0.11 to 0.17.the k values in 2-5 mm of P.asperata and in 0-2 mm of A.faxoniana were markedly promoted in the gaps,butinhibited on 5-10 mm of two needle species.2.The root C,N and P concentrations of three diameter in the forest gap and canopywere significantly changed along time.We observed significant difference in Cconcentration between two species,but not in diameter classes.C content in 0-2mm root diameter was lower than 2-5 mm and 5-10 mm roots.The root Nconcentration in three root diameters of two needle species increased during thedecomposition,and showed significant difference between species and diameter,that is,the root N content decreased with increasing diameters.The root Pconcentration also exhibited difference in species and diameters,and was: 0-2mm>2-5 mm>5-10 mm,after two years decomposition.3.Root C kept in releasing during the decomposition.Forest gap has no significanteffected on the root C remaining and the effect of gap on C remaining varied insampling dates,that is,the C releasing of 2-5 mm and 5-10 mm roots wassuppressed in gap in summer.Root N went through a fast releasing in the firstwinter,and then gradually accumulated during the subsequent decompositionstages.The promotion effect of gap on the N releasing of three diameter mainlyoccurs in summer.Root P showed a pattern of release-enrichment-release,the gapin the forests showed a objective effect on root P releasing and major in winter oftwo years.4.The root humus,humic acid and fulvic acid exhibited significant differences intree species,diameter and times.The root humus content in three diametersmarkedly increased in winter and decreased in summer;after two yearsdecomposition,the humus content in 0-2 mm and 2-5 mm root was significantlyhigher than 5-10 mm.the humic acid of two conifers mainly increased at thebeginning and the end of the decomposition,and the humic acid contentdecreased with the increasing diameters.The root fulvic acid content decreased inthe first winter and increased until the winter of second year,and the difference ofroot diameter on fulvic acid was not significant.5.The accumulation of root humus occurred in winter and released in summer,forest gap showed an objective influence on humus releasing in 0-2 mm of P.asperata,but negatively effect on 2-5 mm.the root humic acid kept inaccumulation in the two years decomposition experiment,and the gap inhibitedon the accumulation of humic acid.The root fulvic acid kept in releasing withdecomposition,and gap showed a promotion during these times.Besides,forestgap has a significant influence on the humic acid: fulvic acid ratios,and the valuein the gap was higher than canopy.The humification degree showed a risingtendency in the first one and a half year and gradually declined from the secondsummer,and the gap did not affect root humification.