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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]

Knowledge of CO 2 emissions under different slope gradients and positions and its controlling factors is critical in accurately estimating CO 2 emissions and carbon cycling on the slopes of eroded regions. In this study, three east-facing plots of 100 m 2 (20 m × 5 m) with a slope gradient of 0.5° (S 0.5 ), 1° (S 1 ), and 3° (S 3 ) were established in an eroded gully of the semi-arid Loess Plateau, China. The CO 2 emission, temperature, moisture, runoff, sediment, fine root biomass and grain yield of these three plots were measured from October 2013 to September 2015 to investigate the relationship between slope gradients and soil CO 2 emissions. The results showed that the mean annual cumulative CO 2 emissions at S 1 and S 3 (731.0 ± 65.1 and 628.3 ± 74.8 g C m −2 year −1 ) were about 13.4% and 25.5% lower than that at S 0.5 (843.7 ± 84.9 g C m −2 year −1 ). The CO 2 emissions were higher at bottom slope than at upper slope, with an increase of 26.2% at S 3 , 22.9% at S 1 and 14.5% at S 0.5 , respectively. The mean soil moisture ranged from 40.8% to 44.8% water-filled pore space (WFPS) among the slope gradients, and from 35.8% to 45.6% WFPS among the slope positions. There was a significant difference in mean fine root biomass among different slope gradients (S 0.5 > S 1 > S 3, P < 0.05), but no significant difference among different slope positions. The mean soil organic carbon (SOC) ranged from 8.8 g kg −1 at S 3 to 9.9 g kg −1 at S 0.5, and that at the bottom and middle slope were higher than that at the upper slope at S 1 and S 3. Slope differentiated soil moisture content and redistribution, and the thus derived spatial differences in fine root biomass and crop yields, was the major factor influencing the soil CO 2 emissions among slope gradients and positions. Slope gradients and positions should be considered when estimating soil CO 2 emissions and carbon cycling in the complex and fragmented topography regions. [ABSTRACT FROM AUTHOR]