Interrelation of soil water and plant water revealed by hydrogen-oxygen
isotopes across alpine shrub and grassland in northern Qinghai-Tibet
Plateau
Abstract
The alpine grassland shrubbization of the northern Qinghai-Tibet Plateau
on the background of global change and overgrazing, is a prominent and
serious problem. However, the water competition ability of shrubs and
alpine grasslands is rarely reported. Here, we tracked the δ
18O and δ 2H of soil water, plant
water, precipitation, and groundwater, analysed sources of water use in
shrub and grassland by Mix SIAR model. Our results showed that both δ
18O and δ 2H in soil, precipitation,
and plant varied significantly over time, groundwater remained
relatively stable in P. fruticosa shrub and alpine grassland
sites during observation. Considering groundwater, precipitation, soil
water, and plant water, a progressive enrichment in δ
18O or δ 2H existed from groundwater
and precipitation to soil water to plant water for each month. Alpine
grassland was more susceptible to drought stress, had a stronger
partitioning effect in dynamic transport than shrub. The P.
fruticosa shrub displayed more flexible water utilisations, and was
more competitive for water than grasslands. Furthermore, the plants in
alpine shrub and grassland reached water use balance in August. Shrubs
degraded from alpine grassland changed water use pattern of grassland,
thereby changing soil water storage. These results contribute to
in-depth understanding the alpine grassland shrubbization from water use
patterns of grassland and shrub plants on the northern Qinghai-Tibet
Plateau.