The effect of <sup>18</sup>O‐labelled water vapour on the oxygen isotope ratio of water and assimilates in plants at high humidity

Lehmann, Marco M.; Goldsmith, Gregory R.; Schmid, Lino; Geßler, Arthur; Saurer, Matthias; Siegwolf, Rolf

doi:10.1111/nph.14788

Cited by 59 publications

(104 citation statements)

References 76 publications

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“…This difference is larger than the range of 18 O-enrichment observed for the upper 10 cm depth of soil water under tropical humid forests (2-3 ‰; Liu et al, 2008;Stahl et al, 2013), suggesting that evaporative isotope signatures of both soils and leaf water imprinted the Globular granulate phytolith type. This is in line with recent 18 O-labelling experiment showing that the 18 O-enriched oak phloem water may exchange with xylem water under low transpiration rates (Lehmann et al, 2018).…”

Section: Imprint Of Changes In Atmospheric Rh On the 17 O-excess Of Psupporting

confidence: 77%

“…Stem water is usually used as an analogue of soil water when modelling δ 17 O LW and δ 18 O LW (Landais et al, 2006;Li et al, 2017). However, in the stem, water in the phloem that is bidirectional (moves up and down the plant's stem) receives the contribution of evaporating leaf water, and water in the xylem that is unidirectional (moves up the plant's stem) may exchange with phloem waters (Lehmann et al, 2018). Consequently one may expect the isotope composition of stem water to be slightly different than that of soil water (Berkelhammer et al, 2013;Treydte et al, 2014).…”

Section: Discussionmentioning

confidence: 99%

“…In the natural environment, a first-order approximation for the isotope composition of water vapor is to consider equilibrium with precipitation. As a result of water-vapor equilibrium fractionation and soil water 18 O-enrichment, this can lead to a water vapor 18 Odepleted by 10-13 ‰ compared to the soil water (Landais et al, 2006;Lehmann et al, 2018). In this case the predicted λ transp (equivalent to λ LW−SW ) decreases with increasing humidity.…”

Section: Irrigation and Soil Watersmentioning

confidence: 99%

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

et al. 2018

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Abstract. Continental atmospheric relative humidity (RH) is a key climate parameter. Combined with atmospheric temperature, it allows us to estimate the concentration of atmospheric water vapor, which is one of the main components of the global water cycle and the most important gas contributing to the natural greenhouse effect. However, there is a lack of proxies suitable for reconstructing, in a quantitative way, past changes of continental atmospheric humidity. This reduces the possibility of making model-data comparisons necessary for the implementation of climate models. Over the past 10 years, analytical developments have enabled a few laboratories to reach sufficient precision for measuring the triple oxygen isotopes, expressed by the 17 O-excess ( 17 O-excess = ln (δ 17 O + 1) -0.528 × ln (δ 18 O + 1)), in water, water vapor and minerals. The 17 O-excess represents an alternative to deuterium-excess for investigating relative humidity conditions that prevail during water evaporation. Phytoliths are micrometric amorphous silica particles that form continuously in living plants. Phytolith morphological assemblages from soils and sediments are commonly used as past vegetation and hydrous stress indicators. In the present study, we examine whether changes in atmospheric RH imprint the 17 O-excess of phytoliths in a measurable way and whether this imprint offers a potential for reconstructing past RH. For that purpose, we first monitored the 17 O-excess evolution of soil water, grass leaf water and grass phytoliths in response to changes in RH (from 40 to 100 %) in a growth chamber experiment where transpiration reached a steady state. Decreasing RH from 80 to 40 % decreases the 17 Oexcess of phytoliths by 4.1 per meg/% as a result of kinetic fractionation of the leaf water subject to evaporation. In order to model with accuracy the triple oxygen isotope fractionation in play in plant water and in phytoliths we recommend direct and continuous measurements of the triple isotope composition of water vapor. Then, we measured the 17 O-excess of 57 phytolith assemblages collected from top soils along a RH and vegetation transect in inter-tropical West and Central Africa. Although scattered, the 17 O-excess of phytoliths decreases with RH by 3.4 per meg/%. The similarity of the trends observed in the growth chamber and nature supports that RH is an important control of 17 O-excess of phytoliths in the natural environment. However, other parameters such as changes in the triple isotope composition of the soil water or phytolith origin in the plant may come into play. Assessment of these parameters through additional growth chambers experiments and field campaigns will bring us closer to an accurate proxy of changes in relative humidity.

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Section: Imprint Of Changes In Atmospheric Rh On the 17 O-excess Of Psupporting

confidence: 77%

Section: Discussionmentioning

confidence: 99%

Section: Irrigation and Soil Watersmentioning

confidence: 99%

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

et al. 2018

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“…To quantify the effects of labelling, δ 18 O values of leaf water and assimilates during the 9‐hr fog event were corrected for natural isotope abundances (Lehmann et al, ).

{Δδ}^{18} normalO = δ^{18} O_{fog} - δ^{18} O_{prefog},

where δ 18 O fog is the isotope ratio of a sample taken during or at the conclusion of the 9‐hr labelling period and δ 18 O prefog is the isotope ratio of a sample taken before labelling start (at 08:30 a.m.).…”

Section: Methodsmentioning

confidence: 99%

“…Our understanding on how δ 18 O V signals are transferred to δ 18 O of plant organic matter and assimilates is even more limited. Research to date has demonstrated that variation in δ 18 O LW induced by step changes in δ 18 O V can be incorporated into δ 18 O of plant organic matter, and the incorporation may differ among different sugar compounds (Lehmann et al, ; Studer, Siegwolf, Leuenberger, & Abiven, ). However, it remains unclear if the observed compound‐specific pattern, with some compounds being more sensitive to water vapour‐induced δ 18 O LW variations than others, can be generalized among species and growth forms.…”

Section: Introductionmentioning

confidence: 99%

The ¹⁸O‐signal transfer from water vapour to leaf water and assimilates varies among plant species and growth forms

Lehmann

Goldsmith

Mirande-Ney

et al. 2019

Plant Cell & Environment

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The 18O signature of atmospheric water vapour (δ18OV) is known to be transferred via leaf water to assimilates. It remains, however, unclear how the 18O‐signal transfer differs among plant species and growth forms. We performed a 9‐hr greenhouse fog experiment (relative humidity ≥ 98%) with 18O‐depleted water vapour (−106.7‰) on 140 plant species of eight different growth forms during daytime. We quantified the 18O‐signal transfer by calculating the mean residence time of O in leaf water (MRTLW) and sugars (MRTSugars) and related it to leaf traits and physiological drivers. MRTLW increased with leaf succulence and thickness, varying between 1.4 and 10.8 hr. MRTSugars was shorter in C3 and C4 plants than in crassulacean acid metabolism (CAM) plants and highly variable among species and growth forms; MRTSugars was shortest for grasses and aquatic plants, intermediate for broadleaf trees, shrubs, and herbs, and longest for conifers, epiphytes, and succulents. Sucrose was more sensitive to δ18OV variations than other assimilates. Our comprehensive study shows that plant species and growth forms vary strongly in their sensitivity to δ18OV variations, which is important for the interpretation of δ18O values in plant organic material and compounds and thus for the reconstruction of climatic conditions and plant functional responses.

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Phloem water isotopically different to xylem water: Potential causes and implications for ecohydrological tracing

et al. 2022

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The stable isotopes of hydrogen and oxygen in xylem water are often used to investigate tree water sources. But this traditional approach does not acknowledge the contribution of water stored in the phloem to transpiration and how this may affect xylem water and source water interpretations. Additionally, there is a prevailing assumption that there is no isotope fractionation during tree water transport. Here, we systematically sampled xylem and phloem water at daily and subdaily resolutions in a large lysimeter planted with Salix viminalis. Stem diurnal change in phloem water storage and transpiration rates were also measured. Our results show that phloem water is significantly less enriched in heavy isotopes than xylem water. At subdaily resolution, we observed a larger isotopic difference between xylem and phloem during phloem water refilling and under periods of tree water deficit. These findings contrast with the expectation of heavy‐isotope enriched water in phloem due to downward transport of enriched leaf water isotopic signatures. Because of previous evidence of aquaporin mediated phloem and xylem water transport and higher osmotic permeability of lighter hydrogen isotopologues across aquaporins, we propose that radial water transport across the xylem–phloem boundary may drive the relative depletion of heavy isotopes in phloem and their relative enrichment in xylem.

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The effect of ¹⁸O‐labelled water vapour on the oxygen isotope ratio of water and assimilates in plants at high humidity

Abstract: Summary

Cited by 59 publications

References 76 publications

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

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

The ¹⁸O‐signal transfer from water vapour to leaf water and assimilates varies among plant species and growth forms

Phloem water isotopically different to xylem water: Potential causes and implications for ecohydrological tracing

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The effect of 18O‐labelled water vapour on the oxygen isotope ratio of water and assimilates in plants at high humidity

Abstract: Summary

Cited by 59 publications

References 76 publications

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

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

The 18O‐signal transfer from water vapour to leaf water and assimilates varies among plant species and growth forms

Phloem water isotopically different to xylem water: Potential causes and implications for ecohydrological tracing

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The effect of ¹⁸O‐labelled water vapour on the oxygen isotope ratio of water and assimilates in plants at high humidity

The ¹⁸O‐signal transfer from water vapour to leaf water and assimilates varies among plant species and growth forms