The Study Of Carbon Cycl E Of Qinghai Spruce Forest In The Middle Part Of Qilian Mountains

Qinghai spruce (Picea crassifolia) is the dominant species in Qilianshan national nature reserve, playing a critical role on the maintenance of ecosystem biodiversity and ecological functions, especially on the function of water conservation. The ecosystem of Qilian Mountains, located in the northeast margin of Tibet Plateau, is very sensitive to global warming, and ecological damages caused by global warming might be irreparable. However, the understanding about the main contributor of climate warming-carbon cycle in Qilian Mountains is insufficient, let alone the interaction between carbon cycle and global warming. In this study, soil CO2efflux in Qinghai spruce, the most uncertain and variable part of carbon cycle, was investigated along an elevation gradient from2611m to3101m, covering the main distribution area of Qinghai spruce. Soil CO2efflux includes soil respiration (bare soil CO2efflux) and moss CO2efflux. The aim is to identify its controlling factors on temporal and spatial variability of soil CO2efflux in order to obtain reliable regional estimation of soil CO2efflux. Simultaneously, Dailydaycent model, the latest version of CENTURY model, was adopted to assess and analyze the dynamic of carbon cycle of Qinghai spruce forest in six climate scenarios. Six climate scenarios are air temperature increased2℃(T); precipitation increased10%(P); double CO2concentration in atmosphere (CO2); air temperature increased2℃plus precipitation increased10%(T+P); air temperature increased2℃plus double CO2concentration in atmosphere (T+CO2); and air temperature increased2℃plus precipitation increased10%plus double CO2concentration in atmosphere (T+P+CO2). This may help us to understand the potential dynamics of carbon cycle of Qinghai spruce forest, such as the role of Qinghai spruce as carbon sink or carbon source in the future, and be useful for making strategies in advance. The main conclusions as follows:Part1-Soil CO2efflux in Qinghai spruce:(1)The diurnal variability of soil respiration in Qinghai spruce is mainly controlled by air temperature. The monthly variability of soil respiration is controlled together by soil temperature and soil moisture. Soil temperature and soil moisture can explain50.3%,77.3%,53.2%,92.2%,78.7%and69.4%of the temporal variability of soil respiration from Plotl to Plot6, respectively. But the effect of soil temperature on soil respiration is confounded by soil moisture at lowlands (Plotl-Plot3). Soil moisture plays a more important role than soil temperature during drought period at lowlands. And soil temperature always plays the primary role on soil respiration at highlands (Plot4-Plot6).(2) Soil water content was the factor causing the spatial variability of soil respiration at lowlands, leading the value of soil respiration at Plot2is the maximum. While air temperature was the factor causing the spatial variability of soil respiration at highlands, leading the value of soil respiration at Plot6is larger than others. There was no significant correlation between soil respiration and topography, stand characteristics, but aspect and LAI could affect soil respiration by inducing higher air temperature at Plot6. Soil temperature and soil water content can explain52%and75.1%of the spatial variability of soil respiration at lowlands and highlands, respectively.(3) Moss CO2efflux, including CO2from moss respiration and excluding CO2from moss photosynthesis, is usually smaller than soil respiration. When taking moss coverage and moss photosynthesis into account of soil CO2efflux, forest floor net CO2efflux was smaller23.71%than soil respiration at study area.Part2-The dynamics of carbon cycle of Qinghai spruce forest in future climate scenarios basing on CENTURY model:(1) Dailydaycent has been proved can be used to simulate the carbon cycle of Qinghai spruce forest, but the magnitude of simulated soil respiration was lower than that of observed.(2) NPP and plant biomass declines10.74%and7.58%in T scenario at the end of21st century. However, NPP and plant biomass increases in P, CO2, T+P, T+CO2and T+P+CO2scenarios, while NPP increases23.62%,41.52%,11.59%,30.81%and58.40%at the endof21st century, and plant biomass increases17.53%,20.36%,8.80%,11.77%and31.70%, respectively.(3) Heterotrophic respiration only declines with decreasing5.91%at the end of21st century in T scenario. In other climate scenarios, heterotrophic respiration increases at the end of21st century. In P scenario, it increases16.57%. In CO2scenario, it increases20.63%. In T+P scenario, it increases9.85%. In T+CO2scenario, it increases14.62%. In T+P+CO2scenario, it increases33.13%.(4) Soil carbon stock increases1.65%and3.67%at the end of21st century only in CO2and P scenarios. In other climate scenarios, soil carbon stock decreased at the late of21st century. In T scenario, it decreases9.53%. In T+P scenario, it decreases8.19%. In T+CO2scenario, it decreases6.28%. In T+P+CO2scenario, it decreases3.95%.(5) The ecosystem of Qinghai spruce releases2442.07,789.88and161.21gC/m2in T, T+P and T+CO2scenarios between2010-2100, respectively, showing it is potential to become a carbon source. While in P, CO2and T+P+CO2scenarios, the ecosystem of Qinghai spruce absorbs1886.45,2662.32and1855.69gC/m2between2010-2100, respectively.