4.3. Implications for meadow eco-hydrological processes
In this study, δ18O and δ2H at the
grassland site were greater than at the shrub site during the growing
season, but almost the same during the withering season, indicating that
grassland plant water had a stronger dynamic fractionation effect in the
process of transportation and was more sensitive to environmental
conditions. Furthermore, plants at the shrub site displayed more
flexible water use patterns that shifted shrub water sources between
shallow water and deep soil water, and the grassland site was more
susceptible to drought stress. From this perspective, alpine shrub sites
on the QPT were formed from the long-term encroachment of P.
squamosa . This result is consistent with the results published
previously by many other researchers who found that shrub populations
are a result of the proliferation and range expansion of woody plant
species in arid and semiarid grassland ecosystems (Van Auken, 2000;
Maestre et al., 2009; Archer et al., 2017) , and that areal expansion of
shrubs is one of the most threatening forms of grassland degradation in
arid and semiarid areas (Eldridge et al., 2011). Shrubs from alpine
grassland leaded to changes in grassland water use, thereby changing
soil water storage(Li et al., 2022).
Many previous studies have shown that vegetation has profound effects on
maintaining local hydrological processes (Feng, et al., 2016; Jia et
al., 2017). Plant water use strategies can be used to exploring all
available water sources by isotopic compositions of xylem water (Wu, et
al., 2019). The contrasting plant water use patterns identified in our
study contribute to the differential sensitivity to interannual
variations of available moisture input. Hence, appropriate management
measures, such as recovering natural environmental characteristics and
moisture status, should be implemented to maintain grassland ecosystem
sustainability.
5. Conclusions and future
directions
The δ18O and δ2H values of
precipitation, soil water, and plant water varied significantly over
months and water sources at the alpine grassland and P. fruticosashrub sites on the QTP. The relationships of δ18O and
δ2H indicated that both soil evaporation and plant
transpiration at the P. fruticosa shrub site were relatively
lower than they were at the alpine grassland site. The grassland plant
water had a stronger dynamic fractionation effect in the process of
transportation and was more sensitive to environmental conditions, but
the plants at the P. fruticosa shrub site displayed more flexible
water use patterns that shifted shrub water sources between shallow soil
water and deep soil water. Moreover, the relationship in
δ18O and δ2H between precipitation
and plant water, and the factors influencing precipitation maybe
resulted from various possibilities. These results promote better
understanding of the interface between plant and surrounding soils
between P. fruticosa shrub and alpine grassland sites, provide
guidance for meadow management from the perspective of eco-hydrological
processes on the QTP.
Although our study used advanced technology exploring the interrelation
of soil water and plant water at the alpine grassland and P.
fruticosa shrub sites and drawn important conclusions in-depth
understanding of eco-hydrological processes, the factors influencing
δ18O and δ2H values maybe resulted
from various possibilities. These possibilities need to be further
examined through greater variety of species, more potential water
sources, multi-site continuous observation, and longer time scales in
the future.