Abstract
Non-native vegetation with high canopy closure can alter the equilibrium
relationship between soil water and plant growth into a non-equilibrium
relationship leading to soil degradation, vegetation decline and crop
failure in the most part of water- limited regions. There is a need for
the application of a novel theory in the assessment and the adjustment
of non-equilibrium relationships to facilitate the sustainable
management of non-native vegetation in the course of vegetation
restoration in such regions. Therefore, a novel theory, Soil Water
Resources Use Limit by Plant (SWRULP) has been developed. SWRULP refers
to the amount of water stored in the maximum infiltration depth (MID) at
which the soil moisture content in each layer is equivalent to the
wilting coefficient. The wilting coefficient is expressed by the wilting
coefficient of indicator plants in a plant community. SWRULP is an index
for assessing plant overuse of soil water resources and the estimation
of the starting time to regulate the relationship between soil water and
plant growth in addition to the selection of the most suitable tree or
plant species for vegetation restoration activities. To better
understand SWRULP, in the present study, the SWRULP was assessed in a
Caragana shrubland and an alfalfa grassland in semiarid loess hilly
region. The results showed that the wilting coefficient varied with soil
depth, and the SWRULP changed based on site conditions and vegetation
type. When the soil water resources were equivalent to the SWRULP, soil
water influenced plant growth considerably and caused the discoloration
of sclerophyllous plants, abscission, cessation of growth, and soft leaf
plant wilt. Under such conditions, the relationship between soil water
and plant growth should be regulated based on soil water carrying
capacity for vegetation to achieve sustainable use of soil water
resource and sustainable management of forest and grassland and
utilization, in addition to sustainable development.