Stable isotopes in leaf water of terrestrial plants

Abstract

Leaf water contains naturally occurring stable isotopes of oxygen and hydrogen in abundances that vary spatially and temporally. When sufficiently understood, these can be harnessed for a wide range of applications. Here, we review the current state of knowledge of stable isotope enrichment of leaf water, and its relevance for isotopic signals incorporated into plant organic matter and atmospheric gases. Models describing evaporative enrichment of leaf water have become increasingly complex over time, reflecting enhanced spatial and temporal resolution. We recommend that practitioners choose a model with a level of complexity suited to their application, and provide guidance. At the same time, there exists some lingering uncertainty about the biophysical processes relevant to patterns of isotopic enrichment in leaf water. An important goal for future research is to link observed variations in isotopic composition to specific anatomical and physiological features of leaves that reflect differences in hydraulic design. New measurement techniques are developing rapidly, enabling determinations of both transpired and leaf water δ(18) O and δ(2) H to be made more easily and at higher temporal resolution than previously possible. We expect these technological advances to spur new developments in our understanding of patterns of stable isotope fractionation in leaf water.

The triple oxygen isotope composition of phytoliths as a proxy of continental atmospheric humidity: insights from climate chamber and climate transect calibrations

“…This absence of a relationship between 17 O-excess and tree cover density is also mirrored in Fig. 4 Cernusak et al, 2016;Landais et al, 2006;Li et al, 2017). The average value of λ LW−IW (0.519) is close to the value of θ diff calculated for the diffusion of vapor in air (0.518; Barkan and Luz, 2007).…”

“…It has been shown that the δ 18 O Phyto of grass stems weakly affected by transpiration correlated with the δ 18 O signature of soil water (δ 18 O SW ) and the atmospheric temperature, as expected for a polymerization of silica in isotope equilibrium with the plant water (Webb and Longstaffe, 2000. It has also been shown that δ 18 O Phyto from grass leaves correlated with RH, as expected for an evaporative kinetic isotope enrichment of the leaf water (e.g., Cernusak et al, 2016) imprinted on δ 18 O Phyto . However, because grass stem and leaf phytoliths have the same morphology and are mixed in soil and sedimentary samples, these calibrations were not sufficient for using δ 18 O Phyto of grassland phytolith assemblages as a paleoclimatic signal.…”

“…The predicted value of 0.529 at 100 % RH reflects pure equilibrium in a situation where irrigation water and water vapor are assumed to have similar isotope composition since irrigation water is directly vaporized into the chamber (Table S3), without any fractionation. Sensitivity tests show that regardless of the model chosen (Buhay et al, 1996;Cernusak et al, 2016;Li et al, 2017), estimations of λ LW−IW are very dependent on the isotope compositions of the water vapor (Li et al, 2017), not measured either in our experiment or in previous studies (Landais et al, 2006;Li et al, 2017). In the natural environment, a first-order approximation for the isotope composition of water vapor is to consider equilibrium with precipitation.…”

“…In grasses, leaf water is expected to be more prone to evaporative enrichment than stem water, and inside the leaf itself, the heterogeneity of evaporative sites repartition and water movements can lead to a significant heterogeneity in the δ 18 O signatures of water and phytoliths (Cernusak et al, 2016;Helliker and Ehleringer, 2000;Webb and Longstaffe, 2002). However, soil top phytolith assemblages likely record several decades of annual bulk phytolith production and their isotope composition is expected to be an average.…”

Quantification of dynamic soil–vegetation feedbacks following an isotopically labelled precipitation pulse

“…This opens the door for large-scale assessment of the soil-vegetation-atmosphere interactions in the water cycle. In particular, these developments have enhanced the spatial and temporal resolution tremendously, furthering the understanding in the fields of plant ecophysiology (Cernusak et al, 2016) and ecosystem physiology (Dubbert et al, 2014a, c).…”