干旱区生态环境知识资源中心

CO2 exchange components of a temperate semi-desert sand grassland ecosystem in Hungary were measured 21 times in 2000-2001 using a closed IRGA system. Stand CO2 uptake and release, soil respiration rate (R-s), and micrometeorological values were determined with two types of closed system chambers to investigate the daily courses of gas exchange. The maximum CO2 uptake and release were -3.240 and 1.903 mu mol m(-2) s(-1), respectively, indicating a rela tively low carbon sequestration potential. The maximum and the minimum R, were 1.470 and 0.226 VMOI(CO2) m(-1) s(-1) respectively. Water shortage was probably more effective in decreasing photosynthetic rates than R-s, indicating water supply as the primary driving variable for the sink-source relations in this ecosystem type.