Ecological Function Of Litter In Several Patterns Of Vegetation Restoration In Rainy Area Of Western China

Litter decomposition is the most key one of the ecological process of forest ecosystem, and plays an important role in nutrients recycling of forest.Litter is the link between vegetation and soil,and can improve ecological function of forest ecosystem by decomposition.The rainy area of Western China is one of the plentiful rainfall areas of China and is also the key area of Grain for Green project in Sichuan province.Now,there are many artificial forests in this area.In this study,we examined litter production, decomposition and ecological function in several patterns of vegetation restoration (Pleioblastus plantation,Bambusa pervariabilis×Dendrocala mopsis plantation,Neosinocalamus affinis plantation,Pleioblastus+Betula luminifera plantation and Betula luminifera plantation)in rainy area of Western China.This study can provide necessary data for nutrients recycling of forest and evaluate ecological benefit of the area by ecological function of litter.The major subject include the dynamics of litter production,the dynamics of litter decomposition,the water conservation function of litter and surface layer soil and the effects of litter on quality of soil,for instance,pyhsicochemical characteristics,microbial biomass and enzyme activity,carbon pool,soil respiration.It is showed that:The amount of litter layer and annual litter production of the plantations were in a order of Bambusa pervariabilis×Dendrocala mopsis＞Pleioblastus+Betula luminifera＞Pleioblastus＞Neosinocalamus affinis＞Betula luminifera.The peak of monthly litter production of Betula luminifera plantation occurred in September,and it was 48%of annual litter production.But the litter of several bamboo plantations mostly occurred the in May,then smoothly decreased and kept stable.No significant difference of litter production between air temperature and rainfalls was detected.So,litter production was chiefly affected by biorhythm of the species.By using litter bag method,experiment was made to study the dynamics of litter decomposition.The results showed that the orders of litter decomposition rate of several plantations were Betula luminifera＞Pleioblastus+Betula luminifera＞Neosinocalamus affinis＞Pleioblastus＞Bambusa pervariabilis×Dendrocala mopsis.The mass loss of several plantations was lower than 50%in 330 d,Betula luminifera plantation was 46.2%, and Bambusa pervariabilis×Dendrocala mopsis plantation was 30.6%.The mass loss of leaf litter was significantly correlated with rainfall.It was found that the modles were fit the data.Litter decomposition processes were simulated Olson's exponential models. which were found the best of fits to the data.According to the models,it needs 4-7 years to reach the 95%of decay rate for the investigated plantations in the experimental region. Decay rates of leaf litter were significantly correlated with the initial leaf litter nitrogen content and C/N but not with other index,and species with high nitrogen contents and C/N exhibited relatively faster decomposition rates.The release rates of carbon showed a continuously increasing pattern in 40 d in all the plantations.At the earlier decomposition stage,the absolute content of nitrogen was decreased in all plantations.Among all there was the most significant nitrogen accumulation,then released at the later decomposition. The variation of phosphorus and calcium concentration of leaf litter was little.The potassium and magnesium of leaf litter moved easily.C/N was superior to lignin/N as calculation index of litter decomposition in the plantations.The order of water-holding capacity of leaf litter in different plantations was Neosinocalamus affinis＞Betula luminifera＞Pleioblastus+Betula luminifera＞Pleioblastus＞Bambusa pervariabilis×Dendrocala mopsis.The model between the water-holding capacity of the leaf litter and the immerse time accorded with exponential function.The model between the water absorption speed and the immerse time was accord with power function.The effect of litter on the soil pyhsicochemical characteristics,microbial biomass and the activity of soil enzyme,carbon pool was studied both in field and laboratory.Litter bags were used in the field to examine the effect.At the same time,the effect was also investigated in the laboratory by constant temperature,illumination and relative humidity. The results were as follows:probably short experiment period,there was not significant variation of soil water-physical properties.The pH value of 5 plantations ranged from 4.12 to 5.42.With decomposition processes of litter in bamboo plantations,pH value decreased. But this variation did not increase with decomposition time.Litter could increase the content of soil total nitrogen.But the variation of soil total nitrogen was not great.NO₃^--N, NH₄⁺-N,available N and water-soluble N are some key factors for growth and development of plant.Litter increased the content of available N and water-soluble N in field and laboratory.Therefore,available N and water soluble-N were more valid index than NO₃^--N and NH₄⁺-N to study the effect of litter on soil nitrogen.The content of available phosphorus and potassium increased with decomposition of litter.Adding leaf litter into soil could obviously increase soil microbial biomass C,N and soil enzyme activity.The litter of Betula luminifera and Pleioblastus+Betula luminifera affected soil microbial biomass more than other plantations because of their lower C/N and quicker decomposition rate.In three bamboo plantations,variation of sucrase,catalase, polyphenol oxidase and urease activity in the litter decomposition processes accorded with decay rate of litter.But celluase and acid phosphatase activity had no law mentioned above.The content of soil total organic carbon and labile carbon of bamboo plantations was greater than Betula luminifera plantation and Pleioblastus+Betula luminifera plantation. According with the result of laboratory incubation experiment,adding litter into soil could increase the content of soil total organic carbon,labile carbon,water-soluble organic carbon and dissolved organic carbon.The effect of litter on soil carbon pool of Pleioblastus+Betula luminifera plantation was superior to other plantations.Soil respiration and the effect of litter on it in several plantations were measured by means of closed-chamber IRGA technique from March 2007 to October 2007.The diurnal variation of soil respiration showed normal distribution,with the minimum value occurring around 8:00-10:00 hours and the maximum value around 14:00 to 16:00 hours.Soil respiration rate was the greatest in August in five plantations,and decreased sharply in October.After July 2007,litter could increase soil respiration rate in the plantations.The order of contribution of litter to soil respiration in different plantations was: Neosinocalamus affinis＞Betula luminifera＞Pleioblastus+Betula luminifera＞Pleioblastus＞Bambusa pervariabilis×Dendrocala mopsis.The soil respiration was positively correlated to ground surface temperature(from the surface to 10 cm depth)in the plantations,and the corrections could be described by exponential function.There was positively relationship between the soil respiration rate and soil labile carbon,but no obviously relationship with microbial biomass carbon and nitrogen.The overall results from this study provided necessary and basic datasets for nutrient cycling,and for contributing to a preliminary understanding of ecological processes of litter of several plantations in rainy area of Western China.Moreover,litter played an important role in improving water-holding and soil quality of the plantations.