气候变化对中国中纬度半干旱草原生产力影响机理的模拟研究

MODELING STUDIES OF RESPONSE MECHANISM OF STEPPE PRODUCTIVITY TO CLIMATE CHANGE IN MIDDLE LATITUDE SEMIARID REGIONS IN CHINA

应用大气植被相互作用模式(AVIM)模拟了内蒙古半干旱草原的净初级生产力和生物量。在此基础上,通过气温和降水变化的敏感性控制试验探讨了气候变化对草地初级生产力的影响机理。研究表明,无论是降水或温度的变化对草地的生产力都有显著影响。降水增加,生产力增加。而温度增加,生产力下降。气候变化对生产力影响的机理是:降水增加改善了土壤的水分供给条件,增强了光合速率,从而提高了生产力。温度增高,一方面可以增加光合速率,另一方面却使蒸散加强,土壤变干,光合速率下降,而后一作用过程在半干旱地区大于前者,因而温度增高使生产力下降。单一气候因子敏感性试验表明,温度增高或降低2℃,年净初级生产力(NPP)变化约20%,中纬度半干旱草地地上生物量可以改变30%以上。降水量变化50%,年NPP改变37%,地上生物量将改变近30%。

The impact of climate and environment on productivity of ecosystems is a complex process. Thorough understanding of these processes is helpful for estimation, prediction and management of productivity of ecosystems. The current coupled model of ecophysiological and physical transfer processes provides a useful tool for simulating response mechanism of ecosystem to climate and environment. It is possible to explore, to a certain extend, the formation process of ecosystem productivity in a changing climate. AVIM used in this study is a dynamical land surface process model that involves both physical transfer processes between soil, vegetation and the atmosphere and plant ecophysiological processes. Therefore, AVIM is capable of calculation of surface fluxes of energy and water and output of carbon flux and productivity. Semiarid steppe in middle latitude is transient climate-ecosystem zone that is sensitive to climate change. The response mechanism of steppe productivity (Net Primary Productivity, NPP) in semiarid areas to temperature and precipitation change was simulated with the AVIM. The results showed that changes of both temperature and precipitation had significant influence on NPP. The increasing of precipitation could increase NPP while the increasing of temperature could decrease NPP. The reason for this is thought that the increasing of precipitation could improve soil water stress and therefore enhance the photosynthesis rate. Increase in temperature could increase both photosynthesis and respiration rates on the one hand, on the other hand, it also decreases soil moisture due to increased evapotranspiration and thus results in the decrease in the photosynthesis rate. Since water condition plays a key role for plant the photosynthesis in semiarid region, so the total effects of temperature increasing caused a decrease in NPP. Sensitive tests show that for semiarid steppe in China, ±2 ℃ temperature change could resulting in a variation of about 20% annual NPP and at least 30% above ground biomass. 50% change of precipitation could create 37% and 50% annual change of NPP and above ground biomass respectively.