The Study On Soil Respiration And CO₂ Release Rate Of Litter Decomposition In Different Forestlands In Hilly Areas Of The Central Sichuan Basin

Global warming is one of the important environment issues, This is caused primarily by increases in "greenhouse" gases such as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide(N₂O), especially CO₂,which is the one of most important greenhouse gases contributes to atmosphere by 60%.Unbalance between source and sink of CO₂ has cased a series of climate problems ,which is threatening the human life and the development of society. Therefore, soil carbon sequestration potential of artificial forest is a key scientific issue of global change mitigation. China has the largest plantation area, with nearly one third of the global total, strengthening the objective research of afforestation and its terrestrial carbon sink, will have an important politic, scientific significance in China. Beech (Quercus glauca), alder(Aluns cremastogyne) and Cypress {Cupressus funebris) are three kinds of typical woodland in this region , especially ,the woodland of cypress was developed successfully on large scale in hilly areas of the central Sichuan Basin from 1970s to 1980s. Has become a primary protective forestry ecosystem in the upper reaches of the Yangtze River.Experiment site is located at Yanting Agro-ecological Station of Purple Soil, Chinese Academy of Science under Chinese Ecosystem Research Network (CERN). The mainly research were focused on the characteristics and influencing factors of soil respiration and the litter fall respiration, Organic matter in soil and organic carbon in litter were measured to estimate the quantity of carbon released by litter decomposition. The results and conclusions were in the followings:(1) Soil respiration in three kinds of woodlands showed remarkably seasonal changes, which were higher in summer and autumn and lower in spring and winter. The mean CO₂ flux of soils covered with litter of beech alder and cypress were 352.3mg·m^-2·h^-1,287.8mg·m^-2·h^-1 and 257.1mg·m^-2·h^-1,respectively, and the mean CO₂ flux of soils with litter-cleared were 269.5 mg·m^-2·h^-1,273.6 mg·m^-2·h^-1 ,237.6 mg·m^-2·h^-1, respectively. The soil respiration rate of forestland soil with litter were higher than the non-litter-covered soils. The litter layer on the soil surface of beech land could low down the emission of CO₂ from soil to atmosphere.(2) Soil temperature and soil moisture were primary impact factors of soil respiration. There was a significant correlation between soil respiration rates and soil temperature at 5cm depth. The temperature sensitivity of soil CO₂ flux was described with Q₁₀value.the Q₁₀ value of soil respiration in three forestlands were 2.17, 1.93, 1.83 respectively. The impact of Soil moisture on soil respiration had a seasonally performance. There were parabola correlations between the soil respiration (except for forestland of breech) and the soil moisture in summer, when the water volume content is at the level about 25%,the soil respiration rate reached at the maximum. There were not correlations between Soil moisture and soil respiration in other seasons.(3) Diurnal changes of soil respiration were accorded with that of the soil temperature in winter and spring. But not, there were unregular peaks displayed in the diurnal changes in summer and autumn because of the high soil temperature and the intense changes of the relative moisture.(4) CO₂ flux released from three kinds of woodlands litter showed remarkably seasonal changes, which were higher in summer and autumn and lower in spring and winter. CO₂ release rate of litter decomposition showed a single-peak curve in forest soil respiration of alder and cypress, and a double-peaks curve in litter of alder tree. The mean CO₂ flux were 28.75mg·m^-2·h^-1, 84.97mg·m^-2·h^-1, 42.59mg·m^-2·h^-1 respectively, and the mean CO₂ flux of soils with litter-cleared were 269.5 mg·m^-2·h^-1, 273.6 mg·m^-2·h^-1 , 237.6 mg·m^-2·h^-1, respectively. The difference of three kinds of released CO₂ flux was significant.(5) There were significant correlations between litter respiration rates and atmosphere temperature ,soil temperature at 5 cm depth and precipitation , With the temperature and precipitation increasing the CO₂ flux(breech, alder) showed an logarithmic increase, there were a exponential correlation and a liner correlation respectively between the CO₂ flux of cypress litter decomposition and temperature and precipitation.Forest soil carbon pool was inputed 16.90tC·hm^-2·a^-1, 11.78tC·hm^-2·a^-1, 5.14 tC·hm^-2·a^-1 respectively by litter lays, and the carbon returned rate of three forest litter were 96.09%, 85.30%and 86.78% respectively. Three kinds of forest soil carbon budget performed carbon sink. The carbon sink efficiency of broad-leaved forestland were larger than coniferous forestland. However, all of carbon sinks function was not obvious.On the other hand, it also reflects that the forests is a huge potential carbon sink in the future if current mixed forests is fostered and managed well. Therefore, foster and management of current forests of alder and cypress is very important for carbon sequestration.