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A better understanding of the response of soil respiration to land-use conversion has important practical implications for ecological restoration in degraded regions. In this study, in situ soil respiration was monitored in a typical land-use sequence on a ridge slope in Wangdonggou watershed of the Loess Plateau, China, during a three-year period from 2011 to 2013. The land-use conversion sequences included cropland (control), apple orchard, grassland, and woodland. The results clearly showed that soil respiration and temperature sensitivity ( Q 10 ) varied significantly with land-use conversion. Soil respiration was decreased by 10% after conversion of cropland to orchard, and increased by 7–46% after conversion of cropland to grassland and woodland. Q 10 was increased by 19% after conversion of cropland to woodland, and decreased by 9–26% after conversion of cropland to grassland and orchard. Soil respiration increased linearly with soil organic carbon (SOC) storage and fine root biomass (<2 mm). The results indicated that root biomass and SOC storage were the major factors influencing Q 10 after conversion of cropland to non-natural ecosystem, and substrate quality or root system adaptability may be the real reason for the difference in Q 10 after conversion of cropland to natural grassland ecosystem. Although soil temperature and moisture significantly influenced soil respiration among the four typical land-use types, their difference derived from land-use conversions could not well explain the difference in soil respiration among land-use conversions. In conclusion, the increases in SOC storage and fine root biomass were the major factors influencing soil respiration among land-use conversions. Thus, conversion of cropland to natural grassland seemed to be the most effective integrated small watershed management to increase soil carbon storage and decrease CO 2 concentration in the loess regions of China. [ABSTRACT FROM AUTHOR]

Land use and topography are two primary factors that affect the spatial distribution of soil organic carbon (SOC) at the watershed scale, particularly in areas of multiple land uses and complex topography on the Loess Plateau. The General Linear Model (GLM) combined with Duncan’s Multiple Range Test (DMRT) were used to conduct variance tests and evaluate the effects of topography (summit, sloping areas and gullies), land use (farmland, orchard, grassland, shrubland and woodland), and their interactions on the vertical and horizontal distributions of SOC at soil depths of 0–10, 10–20, 20–40, 40–60, 60–80 and 80–100 cm. The effects of land use intensified from the summits to the slope areas to the gullies. The SOC concentrations throughout the 100 cm-thick soil profiles in farmland in slope areas and gullies were, respectively, 45.4% ( P < 0.0001) and 55.2% ( P < 0.0001) greater than those on the summits (3.1 g kg −1 ). In slope areas, the SOC concentrations in shrubland and grassland exceeded those in farmland (4.5 g kg −1 ) by 52.1% ( P < 0.0001) and 15.8%, respectively. In addition, in the gullies, the mean SOC concentrations in shrubland and grassland exceeded those in farmland (4.8 g kg −1 ) by 80.6% ( P < 0.0001) and 50.7% ( P = 0.0039), respectively. The SOC concentrations in areas of semi-shaded slope aspects were greater than those in areas of semi-sunny aspects. The enhanced effect of topographic position on SOC may be attributed to the vegetation and the soil conditions associated with the land uses and to the interactions between these variables at the watershed scale. These results could enhance understanding of the effects of environmental factors and their interaction on the spatial variation of SOC in regions with complex topography. These conclusions could have important implications for ecosystem recovery through rational land use changes in the ecologically fragile areas of the Loess Plateau and for improving the accuracy of prediction of SOC in regions of complex topography and land use on the Loess Plateau. [ABSTRACT FROM AUTHOR]