Are leaf physiological traits related to leaf water isotopic enrichment in restinga woody species?

Abstract

During plant-transpiration, water molecules having the lighter stable isotopes of oxygen and hydrogen evaporate and diffuse at a faster rate through the stomata than molecules having the heavier isotopes, which cause isotopic enrichment of leaf water. Although previous models have assumed that leaf water is well-mixed and isotopically uniform, non-uniform stomatal closure, promoting different enrichments between cells, and different pools of water within leaves, due to morpho-physiological traits, might lead to inaccuracies in isotopic models predicting leaf water enrichment. We evaluate the role of leaf morphophysiological traits on leaf water isotopic enrichment in woody species occurring in a coastal vegetation of Brazil known as restinga. Hydrogen and oxygen stable isotope values of soil, plant stem and leaf water and leaf traits were measured in six species from restinga vegetation during a drought and a wet period. Leaf water isotopic enrichment relative to stem water was more homogeneous among species during the drought in contrast to the wet period suggesting convergent responses to deal to temporal heterogeneity in water availability. Average leaf water isotopic enrichment relative to stem water during the drought period was highly correlated with relative apoplastic water content. We discuss this observation in the context of current models of leaf water isotopic enrichment as a function of the Péclet effect. We suggest that future studies should include relative apoplastic water content in isotopic models.

Depth distribution of soil water sourced by plants at the global scale: A new direct inference approach

“…Xylem water in the arid and cold zones had lower d‐excess values (Table ). This is consistent with Bertrand et al (), Yang and Fu (), and Zhu, Wang, Mao, Zheng, and Xu () and values reported for the tropical and temperate zone (Goldsmith et al, ; Hervé‐Fernández et al, ; Rosado, De Mattos, & Sternberg, ). The patterns between climate zones largely reflect those found in the soil water and indicate more fractionation with aridity.…”

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

“…In this study, lower L v in cslf6-1 was likely due to an interaction between a genotype-driven reduction in E related to Sd and an increased mesophyll and xylem water exchange due to lower water flow, which reduced the mixing length between enriched mesophyll water and unenriched water in the xylem Gan et al 2003). Therefore, changes in Sd regulated the relative differences in Δ 18 O LW , but Sd alone did not predict the magnitude of Δ 18 O LW (Rosado et al 2013;Larcher et al 2015). Conversely and similar to Sternberg and Manganiello (2014), higher Δ 18 O e at high light in wildtype and cslf6-2 did not result in higher Δ 18 O LW because increased advective flow (E ) and longer mixing length (L v ) between xylem and mesophyll reduced back diffusion and the impact of Δ 18 O e on Δ 18 O LW .…”

“…The genotypic response of Δ 18 O LW to growth light intensity can be explained within the Péclet effect theory by the corresponding response in stomatal density (Sd). Multiple studies have shown that Sd and stomatal size influence Δ 18 O LW by modifying E andL , and that differences in Sd were sufficient to drive specieslevel differences in Δ 18 O LW between mangrove and nearby freshwater species and acrossArabidopsis stomatal density lines (Rosado et al 2013;Sternberg & Manganiello 2014;Larcher et al 2015;Liang et al 2018). In this study, lower L v in cslf6-1 was likely due to an interaction between a genotype-driven reduction in E related to Sd and an increased mesophyll and xylem water exchange due to lower water flow, which reduced the mixing length between enriched mesophyll water and unenriched water in the xylem Gan et al 2003).…”

Effects of stomatal density and leaf water content on the 18O enrichment of leaf water

“…Therefore, no conclusions, regarding the effect of leaf water content on the isotopic enrichment of leaf water, can be drawn from this study. We note that several other investigators observed no relationship between water content and leaf water isotopic enrichment (Kahmen et al ., , ; Rosado et al ., ).…”