Dynamic And Impact Factor Of Ecosystem Respiration And Phptosynthesis Of Alashan Typical Desert Ecosystem

The field survey work carried out from June to October2012in Nitraria sphaerocarpa+Potaninia mongolica+Krascheninnikovia ceratoides community of desert ecosystem in the territory of Alashan desert. The study work mainly on typical desert ecosystem respiration and photosynthesis rate. Soil respiration rate; Net CO2Exchange; Ecosystem respiration were measured by using a Li-7000H2O/CO2analyzer with an external homemade chamber. Environmental factors including air temperature, soil temperature and soil water content were also measured during the same period. Our results show as follow:1. Soil respiration, ecosystem respiration, aboveground respiration, net CO2exchange rate and community photosynthesis rate of typical desert community have obvious spatial pattern.2. Soil respiration rate diurnal dynamics could be characterized by a mono-peak pattern. The highest soil respiration rates occurred earlier than the temperature peak time in between8:00and10:00am. during dormancy period in growing season (Jun.15th,2012). While in other determination period, the highest soil respiration rates occurred along with the temperature peak time in between12:00am. and14:00pm. Negative value of soil respiration rate was found at night during the later period of the growing season (Oct.5th,2012) and the non-growing season (Oct.28th,2012), and it might be an important clue to find missing sink of the global carbon. Seasonal change of soil respiration could also be described by a mono-peak pattern with the highest value of0.69umol*m-2*s-1(Aug.14th,2012) and the lowest value of0.04umol*m-2*s-1(Oct.28th,2012). We also found that the higher daily mean soil respiration rate, the greater daily amplitude. Significant relationships were found between soil respiration rate and soil temperature at surface, which could be best described by exponential equations, but there are significant seasonal differences of temperature response (R=0.477-0.855). The Q10value based on soil temperature at surface is1.405, which is lower than the average of the global ecosystem, and there also have extraordinary seasonal differences among Q10values (1.507～2.746). Soil water content is the dominating factor for the seasonal variation of soil respiration rate. When the temperature is lower, soil water content have little impact on soil respiration, with the increase of temperature, the influence of soil water content on soil respiration increasing.3. Total respiration and aboveground respiration diurnal dynamics could be characterized by a mono-peak pattern. Seasonal change of total respiration and aboveground respiration could also be described by a mono-peak pattern. Aboveground respiration of community account for14.3～94.8%of total respiration. Significant relationships were found between total respiration rate and soil temperature at surface, which could be best described by exponential equations, but the explanation quantity of temperature on the total respiratory rate is less than20%. The Q10value of Total respiration based on soil temperature at surface is1.3. Soil water content is the dominating factor for the seasonal variation of total respiration rate.4. Diurnal dynamics could be characterized by a mono-peak pattern, and peak time (9:00) is earlier than other ecosystems. Net CO2Exchange day variation is much larger than the change in night. Typical desert community metabolic process is very weak, and, the absorption peak is-2.62umol*m-2*s-1.Soil water content is the dominating factor for the seasonal variation of Net CO2Exchange. Growing season Net CO2Exchange of negative observation day accounted for87.5%of the growing season all observation days, and, desert ecosystems is a carbon sink in growing season.5. Photosynthesis rate diurnal dynamics could be characterized by a mono-peak pattern. Typical desert ecosysterm photosynthesis ability is significantly lower than other ecosysterm, and, the maximum CO2absorption value is-4.65umol*m-2*s-1. Seasonal change of photosynthesis could also be described by a mono-peak pattern, synchronized with the soil moisture seasonal changes. The average of community photosynthetic rate is-0.68umol*m-2*s-1, far lower than most other ecosystem’s photosynthetic rate.