Abstract
Soil moisture scarcity has become the major limiting factor of vegetation restoration in the Loess Plateau of China. The aim of this study is: (i) to compare the spatial distribution of deep (up to 5 m) soil moisture content (SMC) beneath the introduced shrub Caragana korshinskii Kom. under different precipitation zones in the Loess Plateau and (ii) to investigate the impacts of environmental factors on soil moisture variability. Soil samples were taken under C. korshinskii from three precipitation zones (Semiarid-350, Semiarid-410, Semiarid-470). We found that the highest soil moisture value was in the 0–0.1 m layer with a large coefficient of variation. The soil water storage under different precipitation zones increased following the increase of precipitation (i.e., Semiarid-350 < Semiarid-410 < Semiarid-470), although the degree of SMC variation was different for different precipitation zones. The SMC in the Semiarid-350 zone initially increased with soil depth, and then decreased until it reached the depth of 2.8-m. The SMC in the Semiarid-410 zone showed a decreasing trend from the top soil to 4.2-m depth. The SMC in the Semiarid-470 zone firstly decreased with soil depth, increased, and then decreased until it reached 4.6-m depth. All SMC values then became relatively constant after reaching the 2.8-m, 4.2-m, and 4.6-m depths for Semiarid-350, Semiarid-410, and Semiarid-470, respectively. The low but similar SMC values at the stable layers across the precipitation gradient indicate widespread soil desiccation in this region. Our results suggested that water deficit occurred in all of the three precipitation zones with precipitation, latitude, field capacity, and bulk density as the main environmental variables affecting soil moisture. Considering the correlations between precipitation, SMC and vegetation, appropriate planting density and species selection should be taken into account for introduced vegetation management.
Highlights
The Loess Plateau of China covers an area of more than 6.2 ˆ 105 km2, with diverse rainfall, soil, and vegetation patterns
We found that precipitation was the key factor dominating the spatial variations in soil moisture under C. korshinskii shrubs, in the top 5 m of the soils
Soil water storage increased with precipitation, the degree of soil moisture content (SMC) variation varied with different precipitation zones
Summary
The Loess Plateau of China covers an area of more than 6.2 ˆ 105 km , with diverse rainfall, soil, and vegetation patterns. Vegetation restoration is the primary task of ecological rehabilitation here under the “Grain to Green Program” in the Loess Plateau of China [1], aiming to reverse the existing farmlands to their original grassland or woodland condition. The continued expansion of the “Grain to Green Program” might instead lead to dry soil layers, negatively affecting the vegetation sustainability in the Loess Plateau [5] as precipitation is the only source of soil moisture in the region [6]. Since soil moisture is critical in regulating plant growth in these semiarid regions [7], it is crucial to identify the spatial variation and factors affecting soil moisture in different areas of the Loess Plateau of China [8]
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