Abstract
Stock estimates are critical to quantifying carbon and nitrogen sequestration, quantifying greenhouse gas emissions, and understanding key biogeochemical processes (i.e., soil carbon and nutrient cycling). Many studies have assessed soil organic matter and nutrients in different ecosystems. However, the spatial distribution of carbon and nitrogen and the key influencing factors in arid desert steppe remain unclear. Here, we investigated the soil organic carbon (SOC) and soil total nitrogen (STN) to a depth of 100 cm at 126 sites in a desert steppe in northwestern China.SOCandSTNcontents decreased with increasing depth; the highest averageSOCandSTNcontents were 12.70 and 0.65 g kg−1in the surface 5 cm, and the lowest were from 80 to 100 cm (4.49 and 0.16 g kg−1, respectively).SOCdensity (SOCD) andSTNdensity (STND) to a depth of 100 cm averaged 8.94 and 0.45 kg m−2, respectively. The top 1 m of the soils stored approximately 1,041 TgSOCand 52 TgSTNin the study area. Geostatistical analysis showed strong and moderate spatial autocorrelation forSOCDin different soil layers, but the autocorrelation forSTNDgradually weakened with increasing depth.SOCDandSTNDdecreased from southwest to northeast in the study area, along an elevation gradient. Both were significantly positively correlated with topographic variables, precipitation, and the normalized-difference vegetation index, but negatively correlated with temperature and aridity. More than 40% of theSOCDandSTNDspatial variation was explained by elevation, which was the dominant factor. The data and high-resolution maps from this study will support future soil carbon and nitrogen analyses.
Highlights
The most recent report of the Intergovernmental Panel on Climate Change (Cubasch et al, 2013) confirmed that the global climate is warming
The spatial pattern maps created by ordinary kriging showed that SOC density (SOCD) and STN density (STND) decreased from southwest to northeast in the desert steppes of the Hexi Corridor (Figures 4, 5), suggesting a gradient effect
We explored the spatial distribution of SOCD and STND across a large area of typical desert steppe in northern China
Summary
The most recent report of the Intergovernmental Panel on Climate Change (Cubasch et al, 2013) confirmed that the global climate is warming. The soil carbon pool is the largest and most active carbon pool in terrestrial ecosystems and is an important source of atmospheric greenhouse gases. The global soil organic carbon (SOC) pool is about 1,550 Pg, which is twice the atmospheric carbon pool and three times the biological carbon pool (Lal, 2004). Slight changes in the SOC pool will significantly affect the atmospheric carbon content; for example, a change of only 10% of the SOC pool is equivalent to 30 years of CO2 releases caused by human activities (Kirschbaum, 2000). A slight increase in the rate of soil carbon oxidation caused by an increase in temperature will increase the atmospheric CO2 concentration (Davidson and Janssens, 2006)
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