Leaf cell wall properties and stomatal density influence oxygen isotope enrichment of leaf water

Abstract

Oxygen isotopic composition (Δ18OLW) of leaf water can help improve our understanding of how anatomy interacts with physiology to influence leaf water transport. Leaf water isotope models of Δ18OLW such as the Péclet effect model have been developed to predict Δ18OLWO, and it incorporates transpiration rate (E) and the mixing length between unenriched xylem water and enriched mesophyll water, which can occur in the mesophyll (L) or veins (L). Here we used two cell wall composition mutants grown under two light intensities and RH to evaluate the effect of cell wall composition on Δ18OLW. In maize (Zea mays), the compromised ultrastructure of the suberin lamellae in the bundle sheath of the ALIPHATIC SUBERIN FERULOYL TRANSFERASE mutant (Zmasft) reduced barriers to apoplastic water movement, resulting in higher E and L and, consequently, lower Δ18OLW. In cellulose synthase-like F6 (Cslf6) mutants and wildtype of rice (Oryza sativa), the difference in Δ18OLW in plants grown under high and low growth light intensity co-varied with their differences in stomatal density. These results show that cell wall composition and stomatal density influence Δ18OLW by altering the Péclet effect and that stable isotopes can facilitate the development of a physiologically and anatomically explicit water transport model.

The determining factors of hydrogen isotope offsets between plants and their source waters

“…Our results revealed that the effects of temperature and relative humidity on D 18 O Leaf-Xylem and d 2 H offsets varied with climate and spatial scales. Generally, increased temperature promotes plant leaf transpiration thereby increasing D 18 O Leaf-xylem (Cernusak et al, 2022;Ellsworth et al, 2023). An increase in the transpiration rate also leads to an increase in the d 2 H offset (Vargas et al, 2017;Barbeta et al, 2020), which was consistent with our results that temperature promotes plant leaf transpiration, then leads to the more negative d 2 H offsets in the upper reaches and the entire basin scales under the conditions where temperature is the main impacting factor.…”

“…S3c,d) and in the upper reaches (Fig. 4c,d) revealed that the stronger 18 O enrichment in leaf water through transpiration, the stronger negative d 2 H fractionation (Larcher et al, 2015;Barbeta et al, 2020;Casa et al, 2022;Ellsworth et al, 2023). No significant correlations between the d 2 H offset with d 18 O leaf /D 18 O Leaf-xylem were found in the middle reaches with relatively dry conditions, while significantly positive correlations were found in the lower reaches (Fig.…”

“…This may be related to direct relative humidity control on transpiration, or impacts of relative humidity and temperature on transpiration, with respect to the D 18 O Leaf-xylem and d 18 O Leaf water (Cernusak et al, 2022). Previous studies also reported significantly positive relationships between transpirational water loss and isotope fractionation of soil-plant stem water for Persea americana (Vargas et al, 2017;Barbeta et al, 2020), significant linear relationships between transpiration rate and oxygen isotope enrichment of leaf water above source water (Ellsworth et al, 2023) and that leaf water d 18 O was more closely correlated with air relative humidity (Cernusak et al, 2022). From the basin perspective, linkages between climates/D 18 O Leaf-xylem and d 2 H offset represent the integrated features across the environmental gradient (Fig.…”

“…For example, temperature affects d 2 H offsets (significant negative relationship) likely through controlling leaf transpiration via vapor pressure deficit (i.e. usually vapor pressure deficit increases with increasing temperature) in the upper cold and wet environment (Larcher et al, 2015;Barbeta et al, 2020;Casa et al, 2022;Ellsworth et al, 2023). While in the lower reaches with an extremely hot-dry environment, low air humidity (low relative humidity and high vapor pressure deficit) drives plant transpiration accordingly (increased, even at a constant stomatal conductance) affecting the d 2 H offset.…”

“…D 18 O Leaf-Xylem ) to indicate the enrichment in 18 O of leaf water above the d 18 O value of the source water used by plants. These indicators are useful to represent various impacts of stomatal regulation (Larcher et al, 2015;Ellsworth et al, 2023). We also assessed the effect of plant growth form by comparing trees, shrubs, and grasses.…”