| With the change of global climate,forest damage caused by wind increases significantly.Wind-induced wood fall is mainly divided into three ways:root pulling(also known as uprooted treefalls),base breaking and drying.In which,uprooted treefalls has the greatest impact on forest ecosystems.The pit microsite produced by uprooted treefalls has a profound impact on soil formation,nutrient cycling,forest structure and ecological function.The stability of self-sustaining ecosystem in Xiaoxing'an Mountains is degraded due to the obvious increase of uprooted treefalls caused by wind disturbance.Studies have shown that microsites have a certain relationship with microclimate,vegetation renewal,and species diversity.However,up to now,there is no definite conclusion on the relationship between microsite and litter decomposition and soil fertility.Therefore,it is of great significance to explore the changes of soil chemical properties and soil enzyme activities after the decomposition of litter under different types of microsites with different decay classes formed by uprooted treefalls,which is of great significance to enhance the productivity of forest ecosystem and forest management.In this study,two forest types of Picea koraiensis-Abies nephrolepis-Pinus koraiensis forest(PAP)and Tilia amurensis-Pinus koraiensis forest(TAP)with relatively consistent topographic conditions were selected as the research objects to explore the litter decomposition characteristics of uprooted treefalls microsites in Pinus koraiensis mixed forest and its effect on soil fertility.Using litter decomposition bag burial method,the collected litters of Pinus koraiensis,Tilia amurensis and Acer mono were mixed in natural proportions and put into bags.In July 2019,prepared litters were buried in 11 different microsites,including Uprooted treefalls microsite(UT),Pit bottom microsite(PB)and Mound face microsite(MF)microsites with different decay levels(?,?,?)and non-decay levels(Forest gap microsite(FG)and Intact stand microsite(IS))microsites.Three bags were collected monthly from each microsite from August to October,and the litter quality,carbon,nitrogen and phosphorus contents were measured.In July,when the first sampling was carried out,0-5 cm surface soil samples were randomly selected from two forest types with small shovels at UT,PB,MF,FG and IS as initial values.In October,the surface soil samples of 0-5 cm below the litter decomposition bags in each micro-site were taken as the final value.Correlation analysis and variance analysis were used to explore the residual rate of litter decomposition and the enrichment and release characteristics of nutrient content in different microsites,and the main influencing factors of litter decomposition and their relationship with soil fertility were studied.The results show that:(1)The decomposition rates of litter at different microsites in Picea koraiensis-Abies nephrolepis-Pinus koraiensis forest were kIS>kUT>kFG>kMF>kPB;The decomposition rates of litter leaves at different microsites in TAP were kUT>kIS>kFG>kMF->kPB.N and P are the key nutrient elements controlling litter decomposition,and N is the main limiting factor for litter decomposition in different microsites in two forest types.Microsite type is the main influencing factor of litter decomposition,and the effect of decay classes of uprooted treefalls,decomposition time and interaction between factors on litter decomposition is not significant.(2)Before and after litter decomposition,the soil pH of most microsites in TAP was higher than that in PAP.And only some microsites changed significantly due to litter decomposition.Microsite types of two forest types significantly affected soil C,N,P content(p<0.01).Soil C,N,P contents and their ratios in most microsites of PAP were always higher than those of TAP.After litter decomposition,the soil C content of UT and FG microsites increased,while the soil C content of PB,MF and IS microsites decreased in PAP.The change trend of soil C content in TAP was completely opposite;In addition to the increase of soil N content and N:P ratio in MF microsite of TAP,the soil N content and N:P ratio in other microsites of the two forest types decreased;Except for the decrease of soil P content in MF and FG microsites of TAP,soil P content in other microsites of the two forest types increased;Soil C:N ratio of the two forest types in different microsites increased;Soil C:P ratio decreased in all microsites except MF and IS microsites of TAP.Litter C content is the main factor explaining soil nutrient and its ratio in TAP.(3)In TAP,the microsite type,decomposition time and the interaction between them had significant effects on soil C,N and P enzyme activities(p<0.05),and the decay classes of uprooted treefalls had no significant effect on them(p>0.05);The effect of factors on enzyme activity was not obvious in PAP.The trends of soil ?-glucosidase(BG),?-xylosidase(BX)and Cellulase(CBH)enzyme activities were similar.After litter decomposition,most microsite enzyme activities in the two forest types decreased.After litter decomposition,soil ?-1,4-N-acetylglucosaminidase(NAG)enzyme activity of FG and IS microsites in PAP and MF microsites in TAP increased,while soil NAG enzyme activity of other microsites in the two forest types decreased.Soil acid phosphatase(AP)enzyme activity decreased in all microsites of two forest types.In addition,soil total N content and soil N:P ratio were the main factors affecting soil enzyme activity in PAP.Soil C:P ratio,soil water content and litter C:P ratio were the main factors affecting soil enzyme activity in TAP.According to the decomposition characteristics of uprooted treefalls and their microsite underground litters in different decay grades of natural Pinus koraiensis forest,it can be concluded that UT and IS microsite have a greater effect on the decomposition of litter than that of uprooted treefalls,N was the main limiting factor of litter decomposition in the two types of microsite.After litter decomposition,N content decreased and P content increased Soil C,N and P enzyme activities decreased. |
PDF Full Text Request