Abstract
Soil moisture is a central theme in eco-hydrology. Topography, soil characteristics, and vegetation types are significant factors impacting soil moisture dynamics. However, water loss (evapotranspiration and leakage) and its factors of the self-organized vegetation pattern are not clear, which has significant ecologic functions and contributes to different hydrological ecosystem services. From an eco-hydrological point of view, we relied on the observation of rainfall, soil moisture, and soil temperature in the growing season of a drought year to compare soil moisture and temperature dynamics in terms of frequency/probability distribution and water loss among three typical vegetation types in the Qilian Mountains, China. The results indicated that shrubland (the semi-shaded slope) had the highest average soil moisture at the surface soil (0–40 cm) and soil profile during the growing season, while grassland (the south-facing slope) had the lowest daily average soil moisture and highest daily average soil temperature at the surface soil and soil profile. Spruce forest (the shaded slope) had the lowest daily average soil temperature at the surface soil and soil profile (p < 0.001). Water loss among the three vegetation types has a clear positive relationship with soil water content and a negative relationship with soil temperature. The values of water loss between values of water loss at the wilting point and maximum evapotranspiration point tend to occur in wetter soil moisture under the spruce forest and shrubland, whereas that of grassland emerges in drier soil moisture. The spruce forest and shrubland experienced higher water loss than the grassland. Although the spruce forest and shrubland had a better capacity to retain soil water, they also consumed more soil water than the grassland. Soil moisture may be the main factor controlling the difference in water loss among the three vegetation types. These findings may contribute to improving our understanding of the relationship between the soil moisture dynamics and vegetation pattern, and may offer basic insights for ecosystem management for upstream water-controlled mountainous areas.
Highlights
Soil moisture is a critical element in eco-hydrology and the core variable synthesizing the interactions of climate, soil, vegetation, and hydrological cycle [1,2,3]
In order to provide basic information for watershed ecosystem management and gain insights into the soil moisture probability density function (PDF), we examined differences in soil moisture and temperature and the factors influencing these among three typical vegetation types using probability/frequency distribution and water loss methods in a drought year
Soil temperature can affect plant root up-take and evaporation and, water loss [22]. These results indicate that soil moisture at the surface soil could not ignore the vertical difference in water loss caused by the soil moisture and root density in the soil profile, and that soil temperature plays a critical role in soil moisture dynamics
Summary
Soil moisture is a critical element in eco-hydrology and the core variable synthesizing the interactions of climate, soil, vegetation, and hydrological cycle [1,2,3]. Soil characteristics serve as the storage and regulator compartments in the water flow of eco-hydrological systems, as storage of precipitation input allows this water to be used by vegetation, and water flux regulation controls the partition of the rainfall input between the major outflows, including runoff, evapotranspiration, and leakage [10,11,12,13]. These three important factors—topography, soil characteristics, and vegetation types—directly impact soil moisture dynamics in the same climate zone. Vegetation type controls the availability and variability in soil moisture due to the difference of plant transpiration rates, and soil moisture content, in turn, affects transpiration rates related to plant physiological activities [14,15,16,17]
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