Effects Of Seasonal Distribution Of Precipitation Pattern On Subtropical Shrub Litter Decomposition

Shrub is an important part of forest ecosystem,which litter decomposition plays an irreplaceable role in maintaining forest ecosystem productivity,carbon balance and nutrient cycling.As the main water supply source of terrestrial ecosystem,the change of precipitation will have a profound impact on the structure and function of terrestrial ecosystem.In the context of global change,seasonal distribution of precipitation pattern has had the corresponding changes.Seasonal distribution of precipitation pattern is characterized by the variability and complexity of time and space,and generally shows that the “dry season is drier,wet season is wetter,extreme precipitation events occur frequently,and the duration of dry and wet season showed a trend of “extending or shortening” depending on the region.Therefore,the field in-situ litter decomposition bag method was adopted in this study,and Phyllostachys violascens and Alangium chinense,the main shrub species in subtropical forest,were selected as the research objects.In the case of the dry season is drier and wet season is wetter within one year,there are four treatments: “dry and wet season duration remains unchanged”,“dry season extension”,“wet season extension” and“control”.The dynamics of litter mass loss,nutrient release,material degradation and stoichiometric ratio were studied,in order to provide a theoretical basis for predicting the material cycle of forest ecosystems under global change scenarios.The main results are as follows:(1)The decomposition rate of the leaf litter of A.chinense under the four precipitation treatments was significantly faster than that of P.violascens,and the 50% and 95% decomposition time showed a sequential increase from EW-DD-ED-CK(the half-decomposition time of P.violascens are 1.90,2.11,2.11,and 2.71 years,respectively;the time of 95% decomposition are 8.21,9.12,9.12,and 11.72 years,respectively;the half-decomposition time of A.chinense are 0.49,0.53,0.56,and 0.58 years,respectively;the time of 95% decomposition are 2.10,2.28,2.41,2.49 years).(2)The four precipitation treatments had significant effects on the release dynamics of carbon,nitrogen and phosphorus of the shrubs litter.After one year of decomposition test,the carbon release rates of P.violascens and A.chinense were 39.85%-53.61% and 82.98%-92.69%;nitrogen were 34.14%-45.44%and 83.65%-90.98%;phosphorus were 57.26%-65.94% and 82.14%-87.27% respectively.The carbon content of P.violascens and A.chinense decreased gradually,while the nitrogen and phosphorus of P.violascens showed an enrichment-release pattern with the progress of decomposition,while the decomposition of A.chinense was always in a net release state.The element release rates of the two types of shrubs showed EW > DD > ED > CK.(3)The contents of lignin and cellulose in the litter of the two types of shrubs gradually decreased,and after one year,the remaining contents of lignin and cellulose in the litter of P.violascens(The initial mass was 9.01g)were 0.61-0.76 g and 1.96-2.18 g,and that were 0.15-0.26 g and 0.31-0.48 g,respectively for A.chinense(The initial mass was 9.11g).Compared with control,"dry season is drier,wet season is wetter" precipitation treatment significantly improved the material degradation rate;compared with DD,EW treatment increased the wet season contribution rate of material degradation,and material degradation mainly occurred in dry season under ED treatment.(4)With the progress of decomposition,the variation trends of C/N,C/P,N/P and lignin/N of the two shrub litters under different precipitation treatments were more complicated.At the same decomposition stage,the C/N and lignin/N of the litters showed ED > EW,while C/P and N/P showed EW > ED.(5)The water content of litter layer,lignin/N and C/N were the main factors affecting the decomposition of litter under different precipitation treatments.In summary,the heterogeneity of the seasonal distribution pattern of precipitation changes the environment of litter decomposition,which significantly affects the mass loss,element release,substance degradation and dynamic characteristics of ecological stoichiometry.At the same time,the precipitation treatment of “the dry season is drier,wet season is wetter” promoted litter decomposition,and the precipitation treatment of “wet season extension” further accelerated the process of litter decomposition.