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An automated chamber system was employed to measure the soil CO 2 efflux (SCE) in situ for 2 years in a conventional wheat field of the Loess Plateau, China under semi-arid conditions. The annual mean SCE values were 2.44 ± 2.52 lmol m À2 s À1 in 2006 and 2.37 ± 2.33 lmol m À2 s À1 in 2007. Distinct seasonality in the SCE was observed, with significant differences occurring among four periods divided by harvesting, tillage and sowing. In the period from tillage to sowing, the mean SCE values were 2.82 and 2.69 times the annual mean values in 2006 and 2007, respectively, and SCE accounted for 39% and 48% of the annual total within 14% and 18% of the days of the years. Although there were significant exponential correlations between the SCE and soil temperature, and significant linear correlations between the SCE and soil moisture for measurements conducted in the periods before tillage and after sowing each year, the SCE from tillage to sowing was significantly beyond the correlation curves. These findings indicated that seasonal variation in the SCE in a conventional field was controlled not only by soil temperature and moisture, but also by tillage practice. The confounding effects of climate and practice on SCE should be considered when developing ways to mitigate soil carbon loss in conventional cropland in semi-arid regions.

SUMMARYEcological regionalization is a base for rational management and sustainable utilization of ecosystems and natural resources. It can provide a scientific basis for constructing healthy ecological environments and making policies of environmental management. In this paper, based on synthetic analysis of the characteristics of the ecology and environments of China, the principles of ecological regionalization are discussed, and indices and nomenclature of ecological regionalization are proposed. The ecoregions on a national scale are divided. The results show that there are 3 domains, 13 ecoregions and 57 ecodistricts. The present scheme can be used as a framework for ecosystem assessment and management. Based on the ecoregions, measurements of management for forest, grassland, agriculture and wetland ecosystems are recommended. The experience and information can be used within and beyond the national scale for landuse planning, biodiversity conservation and ecosystem restoration.