Relationship between Ecosystem Carbon Fluxes and Canopy Radiometric Temperature Using Infrared Thermometry in a Ryegrass Ecosystem

Using the closed chamber technique daily changes of net ecosystem carbon dioxide (CO₂) exchange (NEE) and ecosystem respiration (R_e) were determined in a ryegrass ecosystem on eight separated days at half hour interval from morning to afternoon in Taiyuan basin, Shanxi province of China. The gross primary production (GPP) was calculated as the difference of NEE and R_e. The objective of the study was to examine the relationship between ecosystem C fluxes and canopy temperature (T_c), air temperature (T_a) and soil temperature (T_s), and finally to explore the possibility that T_c could substitute T_a or T_s for estimate of ecosystem carbon fluxes. The results showed on diurnal scales that the coefficients of determination of both NEE and GPP with T_c were significantly higher than those of the GPP and NEE with T_a, and that the R_e was also closely related with both T_a and T_c on all measurement dates, but that significant correlation of R_e with T_s existed only on 7 out of 8 measurement dates. The determination coefficients between R_e and T_s were lower than those between R_e and both T_a and T_c on diurnal scales. These results suggested that at plot scale T_c also is a good factor for ecosystem carbon fluxes estimate as both T_a and T_s factors. This gives some implications for linking remotely sensed infrared temperature of canopy to ecosystem carbon flux estimate. However, further experiments at ecosystem scale are still needed.