The Variation Of Soil Particle-Sizes Oranic Carbon And Enzyme Activities For Different Vegetation Restoration In The Mid-subtropical Region Of China

Soil organic carbon(SOC)is the most important and active reservior of carbon in terrestrial ecosystems,and also an important factors in the global carbon cycle.Changes of SOC pool were will affecting atmospheric carbon balance.Soil enzyme activity plays an important role in the transformation and cycling of carbon and nitrogen nutrients in forestland,and it also represents the fertility status of the soil.At present,the research on soil particle-size content and soil enzyme activity characteristic is mainly concentrated in the impact of land use change and management measures on SOC pool and enzyme activity,the effect of vegetation succession restoration on the content and distribution of soil particle-size carbon and the dynamic characteristics of enzyme activity are rarely reported.Therefore,this paper is based on four kinds of typical vegetation restoration stages in the middle subtropics:1)Loropetalum chinense+haccinium bracteatum+Rhododendron maresii scrub-grass-land(LVR),2)L.chinense+Cunninghamia lanceolata+Quercus fabri shrubbery(LCQ),3)Pinus massoniana+Lithocarpus glaber+L.chinense coniferous-broad leaved mixed forest(PLL)and 4)L.glaber+Cleyera japonica+Cyclobalanopsis glauca evergreen broad-leaved forest(LAG),In order to elucidate the effects of vegetation restoration stages on soil organic carbon,the soil partical-size fractionation method was adopted to study the dynamic changes and impact factors of soil organic carbon(SOC)concentration and their distributions in different particle-size fractions and soil enzyme activities,then to reveal the mechanism of vegetation restoration on soil physical carbon sequestration and the effect of soil enzyme activity.Its provide scientific basis for restoration and reconstruction,soil carbon storage management of forest vegetation in the subtropical and effective improvement of soil fertility.The main results were summarized as following:(1)LCQ soil bulk density was significantly higher than LVR,PLL and LAG;With vegetation restoration,The percentage of>2?m particles(sand,silt)increased,While that of<2?m clay particle decreased,and Soil texture was clayey,and soil particle composition shifted from silt to clay;The pH of soil was 4.39-5.07,which was acidic,and different vegetation restoration stages was not significant;The contents of BC,BN and BP,TN,TP,AN and AP in the different soil layer increased with vegetation restoration.The soil N/P is 2.5-10.2,and the difference between different vegetation restoration stages is significant.In the initial stage of vegetation restoration,the soil N is limited by N,and with the vegetation restoration,the soil N utilization rate increases,and finally is limited by P.(2)Along vegetation restoration,SOC increased dramatically,and LAG is significantly different from the other three stages of recovery,which was 49.80,30.83 and 12.58 g/kg higher than in LVR?LCQ and PLL in 0—40 cm soil depth,increasing by 65.61%,54.16%and 32.51%,respectively.SOC pool was mainly composed of silt-C and clay-C in LAG,while those were dominated by silt-C and sand-C in PLL,LCQ and LVR.With vegetation restoration,Concentrations of SOC in three particle-sized fractions were increased,the distribut on proportion of sand-C concentrations decreased,obviously,but that of clay-C increased obviously,the results showed that silt-C transferred to clay-C and the clay-C increased.The ratio of POC/MOC decreased,the SOC fixation,protective effect,stability increased in the same layer.(3)Correlation analysis showed that silt-C and clay-C strongly and positively correlated with existing biomass in litter layer(LEB),nitrogen(LN),phosphorus(LP)concentration in litter layer,aboveground biomass(AB),root biomass(RB),community total biomass(CTB),but significantly and negatively correlated with C/N in litter layer,C/P in litter layer,sand-C strongly and positively correlated with soil total N(TN),soil total P(TP),available N(AN),available P(AP),soil C/P ratio,soil N/P ratio,SOC,but significantly and negatively correlated with soil bulk density(BD)and pH,suggesting that the differences in soil particle-size content under different vegetation stages were related to both vegetation and soil properties.The results of principal component analysis and stepwise regression analysis revealed that RB,LN,LC concentration,C/P in litter layer,SOC,soil TN,soil AN,soil C/N ratio,were the dominant factors affecting soil particle-size content during vegetation restoration.Among them,SOC significantly affects the sand-C,followed by soil AN,SOC significantly affects the silt-C,followed by LN concentration,Clay-C are most affected by soil TN.(4)Along vegetation restoration,Soil enzyme activity increased dramatically,and the difference between different vegetation restoration stages was significant.;The activity of Urease(URE)LAG,PLL,LCQ was 69.18%?43.26%?52.57%higher than in LVR,respectively.The activity of Invertase(INV)LAG,PLL,LCQ was 29.90%?13.32%?13.23%higher than in LVR,respectively.The activity of Acid phosphatase(ACP)LAG,PLL,LCQ was 44.29%?39.01%?18.62%higher than in LVR,respectively.The activity of Catalase(CAT)LAG,PLL,LCQ was 48.50%?42.74%?40.42%higher than in LVR,respectively.The enzyme activities of the four soils showed different seasonal characteristics,which were generally performance is:autumn,summer,spring is relatively high,winter is the lowest.There was significant positive correlation between the four enzyme activities and microbial biomass C,microbial biomass N and microbial biomass P.Correlation analysis showed that soil enzyme activity strongly and positively correlated with RB,nitrogen(N),phosphorus(P)concentration in litter layer,AB,CTB,existing biomass in litter layer(except ACP);Path analysis showed that the direct and main influencing factors for URE?INV?ACP?CAT were percentage of sand-C and Silt-C.Furthermore,the residual path cofficients of URE?INV?ACP?CAT activity were high,impying soil factors had a great influence on soil enzyme activity.