Co 2 flux was measured continuously using the eddy covariance technique in a wheatmaize rotation system in the North China Plains from october 2002 to october 2006. The annual and seasonal variation of ecosystem respiration and the bio-environmental controls on them were investigated. The results show that ecosystem respiration (R ec ) in the cropland increased exponentially with soil temperature at 5 cm depth. The temperature sensitivity coefficient (Q 10 ) for ecosystem respiration varied

more »

... 3.5 to 5.4 for wheat and from 2.4 to 4.5 for maize. in the wheat growing season, monthly average R 0 (ecosystem respiration at 0°C) increased linearly with soil temperature and logarithmically with leaf area index (LAI). Monthly average Q 10 decreased logarithmically with R 0 . Residual R ec was significantly correlated with LAI. After considering LAI, the modified Q 10 model could estimate R ec better than before. The simulation results show that annual ecosystem respiration in the wheat-maize rotation system in the North China Plains was 1327, 1348, 1040 and 1171 gC m -2 yr -1 for the 4 years of the study. as a 4-year average, seasonal mean ecosystem respiration in wheat (2.60 gC m -2 day -1 ) was much lower than in maize (6.09 gC m -2 day -1 ). however, integrated ecosystem respiration for the wheat growing season (566 gC m -2 ) was slightly higher than that for maize (520 gC m -2 ). These account for 46.4 and 42.6% of the annual values, respectively.