Vertical variations of soil moisture in response to vegetation
restoration on the Loess Plateau of China
Abstract
Soil moisture is essential for vegetation restoration in arid and
semi-arid regions. Ascertaining the vertical distribution and
transportation of soil moisture under different vegetation restoration
types has a profound impact on the ecological construction. In this
study, the soil moisture at a depth of 500 cm for four typical
vegetation types, including R. pseudoacacia (forestland), C. korshinskii
(shrubland), S. bungeana (abandoned land), and corn (cropland) were
investigated and compared in the Zhifanggou watershed of Loess plateau,
China. Additionally, hydrogen and oxygen stable isotopes were detected
to identify and reflect the characteristics of soil water. The results
showed vertical distribution and transportation of soil moisture have
different variations under different vegetation types. Depth-averaged
soil moisture under S. bungeana and corn increased along the profile as
a whole, while C. korshinskii and R. pseudoacacia showing a trend of
weakly increasing and relatively stable state after an obvious
decreasing trend (0–40 cm). The mean soil moisture under R.
pseudoacacia is lower than other types, especially in deeper layers. In
addition, it was observed that the longer vegetation age, the lower mean
soil moisture, while this phenomenon was unobvious in S. bungeana.
Planting arbor species such as R. pseudoacacia intensified the decline
of soil moisture in the Loess Plateau, this limited the growth of arbor
species in turn. The capacity of evaporation fractionation of soil
moisture followed the sequence: corn > S. bungeana
> R. pseudoacacia > C. korshinskii. Profiles
of δ18O values of soil moisture under different vegetation types are
quite different. On the whole, the δ18O values varied greatly in upper
soil layers and tend to be consistent with the increase of soil depth.
We estimate that piston flow is the main mode of precipitation
infiltration, and the occurrence of preferential flow is related to
vegetation types. These results are expected to help improve the
understanding of the response of deep soil moisture to vegetation
restoration and inform practices for sustainable water management.