Stable isotope analysis of plant water and soil water
across two vegetation types in the
northern Qinghai-Tibet Plateau
Jing
Li 1,2#, Fawei Zhang 1,3#, Yangong
Du 1,3, Yunying Wang 1,2, Yuting
Lan1,3, Mengke Si 1,3, Bo
Fan1,3, Huakun Zhou1,3, Bin
Wang4, Guangmin Cao 1,3*, Xiaowei
Guo1,3*
1 Key Laboratory of Adaptation and Evolution of Plateau Biota,
Northwest
Institute of Plateau Biology, Chinese Academy of Sciences, Xining, China
2 College of Resources and Environment, University of the Chinese
Academy of Sciences, Beijing, China
3 Qinghai Provincial Key Laboratory of Restoration Ecology for Cold
Regions, Xining, Qinghai, China
4 New South Wales Department of Primary Industries, Wagga Wagga
Agricultural Institute, Wagga Wagga 2650, Australia
# These authors contribute equally.
* Correspondence: Xiaowei Guo and Guangmin Cao, Key Laboratory
of Adaptation and Evolution of Plateau Biota, Northwest Institute of
Plateau Biology, Chinese Academy of Sciences, Xining,810008, China;
Email: guoxw@nwipb.cas.cn; Tel
& fax: +86 09716123010
Abstract:
Studying the interrelation of soil water and plant water is essential
for an in-depth understanding of eco-hydrological processes. However,
water use relationships and comparative studies between shrubs and
alpine grassland of the northern Qinghai-Tibet Plateau remain poorly
understood. In this study, we compared δ18O and
δ2H values of water from soil, plant, precipitation,
and groundwater between P. fruticosa shrub and alpine grassland
locations at two neighboring sites in order to better understand the
interface between plant and surrounding soils of shrubs and grasslands
in the northern Qinghai-Tibet Plateau. Our results showed that
δ18O and
δ2H of soil water, precipitation, and plant water
varied significantly over time and water sources in P. fruticosashrub and alpine grassland sites.
Both
soil evaporation and plant
transpiration at the P. fruticosa shrub site were relatively
lower than they were at the alpine grassland site.
Alpine grassland plant water had a
stronger dynamic fractionation effect in the process of transportation
and was more sensitive to environmental conditions. However,
plants at the P. fruticosashrub site displayed more flexible water use patterns, shifted their
water sources between shallow soil water and deep soil water. Shrubs
from alpine grassland leaded to changes in grassland water use, thereby
changing soil water storage. The results of this study will provide
theoretical basis for improving the availability and sustainability of
soil water, provide guidance for meadow management from ecohydrological
processes on the northern Qinghai-Tibet Plateau.
Keyword: Ecohydrological
processes, Alpine meadow water, Qinghai-Tibet Plateau, Stable water
isotopes, P. fruticosa shrub water, Soil water
Introduction
Water is one of the most crucial limiting factors determining the
dynamic trends of plant in arid and semiarid ecosystems (Li et al.,
2013). The availability of the primary water sources (i.e., soil water,
groundwater) absorbed by plants have significant changes spatially and
temporally, and determine the growth status of plants, and the
distribution and growth status of plants affect the ecological structure
and functions of the soil/plant system (White&Smith, 2013; Wu et al.,
2019). In addition, the interaction of soil and plant water is a vital
component of eco-hydrological processes (Dawson&Ehleringer, 1991; Feng
et al., 2016; Chang et al., 2019). Therefore, there is an growing
interest in researching studies on the interface between plants and
surrounding soils (Sprenger et al., 2017; Roebroek et al., 2020).
The Qinghai-Tibet Plateau (QTP) is known as the ”Chinese Water Tower”
and is an essential component of China’s ”three screens and two belts”
ecological security strategic pattern. QTP is particularly vulnerable to
hydrological changes under climate change (He et al., 2020). Data
observed from 2001 to 2018 indicated that both soil water storage and
number of days of seasonal frozen soil declined over that period. Shrub
meadows (Potentilla fruticosa ) and alpine grasslands are the
dominant vegetation types in the QTP. They have important water
conservation functions (Dai et al., 2021), and play an important role in
maintaining the water-heat balance and ecological barrier function of
the QTP (Dai et al., 2019a). Previous studies of soil and plant between
grasslands and shrubs only focused on exploiting different hydrological
niches of plant and soil (Walker et al., 1981), soil
moisture–vegetation feedbacks and their possible effects (D’Odorico et
al., 2007), and functional differences in soil and plant (Ryel et al.,
2008) by modeling. Additionally, physiological and physical
characteristics (Volkmann et al., 2016), such as precipitation patterns
(D’Odorico, et al., 2007), soil water availability (Gow et al., 2018)
and distribution of fine roots (Lanning et al., 2020; Wang et al., 2021)
affect the plant water use patterns, the plants influence soil water
availability of different soil layers (Fu et al., 2017), with shallow
soil water being affected by precipitation, and deep soil water being
affected by groundwater (Feng, et al., 2016). However, on the one hand,
water-use patterns of plants on the QTP only conducted on theAchnatherum splendens grassland (Jiang et al., 2021) and alpine
riparian plants (Huawu et al., 2019), which both have an environment
along the river and located in the west of QTP, on the other hand, many
mechanisms and significance between shrubs and grasslands are not well
understood, and little research on water-use patterns and relationships
between shrubs and grasslands has been conducted on the north of QTP.
The isotopic variation of both plant water and soil water can provide
valuable information on the interactions between plant water and soil
water (Vargas et al., 2017; Che et al., 2019), providing an effective
and powerful method for revealing and partitioning the different
potential water sources used by plants (Dawson et al., 2002;
Rothfuss&Javaux, 2017). During water absorption by roots and
transportation along shoots prior to transpiration, no isotopic
fractionation of water occurs in terrestrial plants (Ehleringer&Dawson,
1992; Dawson, et al., 2002), except for the halophytes concluding
coastal wetland species and woody xerophytes, that H (but not O)
fractionate due to symplastic movement of water during uptake
(Ellsworth&Williams, 2007) (Brum et al., 2019).
In this study, we compared δ18O and
δ2H from different water sources in a pair of
neighboring sites, and distinguished water use sources of P.
fruticosa shrubs and alpine grassland plants on different seasons in
order to in-depth understanding of the interaction of soil water and
plant water for P. fruticosa shrubs and alpine grasslands on the
QTP. The results are expected to provide a theoretical basis for the
management of the alpine grassland ecosystem, and sustainable use of the
soil water in the northern QTP.
2. Materials and methods