Speculations on the application of foliar <sup>13</sup>C discrimination to reveal groundwater dependency of vegetation and provide estimates of root depth and rates of groundwater use

Abstract

Abstract. Groundwater-dependent vegetation is globally distributed, having important ecological, social, and economic value. Along with the groundwater resources upon which it depends, this vegetation is under increasing threat through excessive rates of groundwater extraction. In this study we examined one shallow-rooted and two deep-rooted tree species at multiple sites along a naturally occurring gradient in depth-to-groundwater. We measured (i) stable isotope ratios of leaves (δ13C), xylem, and groundwater (δ2H and δ18O); and (ii) leaf-vein density. We established that foliar discrimination of 13C (Δ13C) is a reliable indicator of groundwater use by vegetation and can also be used to estimate rooting depth. Through comparison with a continental-scale assessment of foliar Δ13C, we also estimated the upper limits to annual rates of groundwater use. We conclude that maximum rooting depth for both deep-rooted species ranged between 9.4 and 11.2 m and that annual rates of groundwater use ranged from ca. 1400 to 1700 mm for Eucalyptus camaldulensis and from 600 to 900 mm for Corymbia opaca. Several predictions about hydraulic and leaf traits arising from the conclusion that these two species made extensive use of groundwater were supported by additional independent studies of these species in central Australia.

Squandering water in drylands: the water‐use strategy of the phreatophyte Ziziphus lotus in a groundwater‐dependent ecosystem

“…To explore the variability in plant resource‐use and establish the link between leaf carbon isotope composition and rooting depth in response of the DGTW gradient (Prieto et al, 2018; Rumman et al, 2018), we also analyzed foliar nutrient concentrations and carbon isotope discrimination in the Z. lotus population. We collected 30 leaves per individual from the same 16 plants associated to the boreholes, stored them in paper bags, and ultimately oven‐dried them at 60°C for 48 h to finely ground to powder.…”

“…Indeed, stable hydrogen (δ 2 H) and oxygen (δ 18 O) isotopes are used to determine the dominant water source for plants, assuming differences in isotopic composition among water sources (Lin and Sternberg, 1993; Dawson et al, 2002). This approach compares the stable isotope composition in xylem water to that in precipitation, soil water, intermediate water of the vadose zone, or groundwater (Moreno‐Gutiérrez et al, 2012; Eamus et al, 2015; Nolan et al, 2018; Rumman et al, 2018). Although this approach is based on the assumption that isotopic fractionation does not occur during root water uptake in terrestrial plants (Dawson and Ehleringer, 1991; Dawson et al, 2002), several studies have reported fractionated isotopic signatures in xylem water of xerophytic and halophytic species (Lin and Sternberg, 1993; Ellsworth and Williams, 2007).…”

“…Particularly, leaf carbon isotope discrimination (Δ 13 C) has been used as a time‐integrated measure of intrinsic water‐use efficiency (WUEi) that depends on the ratio between intercellular and ambient CO 2 concentration (ci/ca) (Flanagan et al, 1992; Moreno‐Gutiérrez et al, 2012; Prieto et al, 2018). Recent studies have shown that leaf (or sapwood) Δ 13 C can respond to changes in rooting depth and groundwater use in phreatophytes; thus, carbon isotopes in leaves can serve as a reliable indicator of depth‐to‐groundwater (DTGW) in dryland ecosystems (Zolfaghar et al, 2014; Garrido et al, 2016; Rumman et al, 2018).…”

Spatiotemporal variations in groundwater and evaporative demand drive ecophysiological functioning of a phreatophyte in drylands

“…This result can be explained by Z. lotus accessing and using groundwater continuously and by avoiding stomatal closure and g s restrictions (Torres-García et al, 2021), as demonstrated by low WUEi, not only at sites with the shallowest water tables but also at the deepest ones. Such behaviour is observed in phreatophytic vegetation with access to groundwater (Nolan et al, 2017b(Nolan et al, , 2018Rumman et al, 2018). Additionally, Z. lotus transpiration rate did not decline in summer; in fact, it increased with VPD, more signi cantly at shallow water tables, suggesting that summer conditions could induce higher rates when su cient groundwater is available (Nolan et al, 2018;Eamus and Prior, 2001), and that groundwater availability to the plant depends on climatic conditions.…”

Algunos Usos De Técnicas De Isótopos Estables en Ciencia Forestal

“…The δ 13 C measured in the dry matter has been a precise estimator of the intrinsic time-integrated water use efficiency for C 3 plants (Farquhar et al, 1989). Also, δ 13 C has been successfully used in the iWUE study of eucalyptus (Eucalyptus) forests (Zolfaghar et al, 2017) and Prosopis tamarugo (Garrido et al, 2016) submitted to depth gradients of water level, as well as roots depth estimation and use of groundwater in different forest communities (Rumman et al, 2018).…”