| In this paper,the eddy covariance data combined with soil temperature and soil water content data from Xilinhot National Climate Observatory were used to analyze respiration process and its key climatic influencing factors of the semiarid stipa grassland ecosystem in Xilin Gol during the growing season from 2010 to 2012. And then the applicability of four different ecosystem respiration models were compared.Furthermore, the reliability of the use of enhanced vegetation index (EVI) inversion of GPP was verified and introduced as a biological factor to improve the existing respiratory model(1) Based on this research, the inter-annual variability of net carbon exchange,respiration and primary productivity of this ecosystem were discussed. The respiration was affected by both soil temperature and soil water content, in which soil water content was an important limiting factor. The precipitation in 2010 and 2011 was less than normal, so this ecosystem suffered from different degrees of drought stress. In these years, the trends of respiration rate were more similar to that of soil moisture. According to the response characteristics of respiration to different soil water content, soil water content was divided into three intervals (VWC<12%, 12%?VWC?20%, and VPWC > 20%), while the trend of respiration rate was more correlated with the trend of soil temperature in 2012, and the water content only had an overall effect on it, when the precipitation is abundant and the soil is moist.(2) The fitting results indicated that Q10 model had better performance than other three models, because of its superiority in functional structure and temperature sensitivity at high temperature and high humidity, insensitive to moisture content at low temperature and high humidity. However,the respiration models based on soil temperature and soil water content cannot reflect the effect of vegetation growth on vegetation autotrophic respiration, so there is some limitation on the simulation ability of total ecosystem respiration.(3 ) The cumulative total ecosystem respiration during growing season in these three years simulated by the Q10 model was 157.32 g C·m-2,138.75 g C·m-2, and 246.32 g C ·m-2. And the total amount of NEE was -110.28 g C ·m-2, -68.79 g C ·m-2 and -310.05 g C·m-2, while the total amount of GPP was 267.52 g C·m-2, 207.57 g C·m-2 and 555.85 g C·m-2.Due to the spatial and temporal distribution of precipitation, the inter-annual variability of soil water content became an important environmental factor affecting the carbon exchange of this ecosystem during the growing season from 2010 to the 2012, and the effect of drought stress on photosynthesis is greater than that of respiration. Therefore, the inter-annual difference of net carbon exchange due to drought stress was more obvious than that of total primary productivity and respiration, and the amount of carbon released by respiration in the dry years accounts for a greater proportion of the photosynthetic carbon fixation.The enhanced vegetation index (EVI) could reflect the growth status of the surface vegetation, and the EVI index was improved as the biological factor to improve the respiration model. The simulation results of the continuous breathing model and the Q10 model were significantly improved (R2 increased by about 0.10).Hence the introduction of biological factors based on remote sensing data in the respiratory model has a good value in the assessment of carbon exchange at the regional scale. |
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