Vertical Distribution and Influencing Factors of Soil Water and Organic Carbon within 21-m Profile on the Chinese Loess Plateau.

Abstract In water-limited regions that have deep soils, plant root systems can extract soil water and nutrients via plant root systems that are deep enough to a depth of 20 m or more, which may play an important role in the global water and carbon cycles. We collected soil samples to a depth of 21 m across the Chinese Loess Plateau (CLP) in order to determine the vertical distributions and influencing factors of soil water content (SWC) and soil organic carbon (SOC). Mean values for SWC, SOC, soil water storage (SWS), and available soil water storage (AWS) in the soil layers had a similar distribution pattern down the profile, which could be divided into three statistically significant different sub-layers. The amount of SWS and AWS in the 21-m profiles varied from 1639 mm to 5669 mm and from 831 mm to 2953 mm, respectively. In the deep soil layer (5-21 m), SOC storage was significantly higher (P<0.01) under forest (47±0.43 kg m^-2) than under cropland (38±0.44 kg m^-2). Within the rooting zone, the factors affecting SWC (i.e., land use and root mass) and SOC (i.e., root length, pH and clay content) variation were different; below the rooting zone, soil texture became a more important factor of affecting SWC, while the factors affecting SOC were soil water content, pH and clay content. Understanding this information is important to regional water and carbon budgets, sustainable land management and the restoration of the ecological environment on the Loess Plateau and possibly in other water-limited ecosystems around the world.

Keywords: Deep soil; Land use; Plant root; Soil water storage; Soil organic carbon management