Evaporative enrichment and time lags between <i>δ</i><sup>18</sup>O of leaf water and organic pools in a pine stand

Barnard, Romain L.; Salmon, Yann; Kodama, Nobuhiro; Sörgel, Karin; Holst, Jutta; Rennenberg, Heinz; Geßler, Arthur; Buchmann, Nina

doi:10.1111/j.1365-3040.2007.01654.x

Cited by 84 publications

(131 citation statements)

References 56 publications

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“…The effective mixing length L for pine needles was 10 cm, and falls well within the range of expected values for P. sylvestris (5-15 cm, see Barnard et al, 2007;Gessler et al, 2009a). The isotope fractionation factor during sucrose synthesis assumed in MuSICA was +25& (Gessler et al, 2009b).…”

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confidence: 75%

Improvement of water and light availability after thinning at a xeric site: which matters more? A dual isotope approach

et al. 2015

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SummaryThinning fosters individual tree growth by increasing the availability of water, light and nutrients. At sites where water rather than light is limiting, thinning also enhances soil evaporation and might not be beneficial. Detailed knowledge of the short-to long-term physiological response underlying the growth responses to thinning is crucial for the management of forests already suffering from recurrent drought-induced dieback.We applied a dual isotope approach together with mechanistic isotope models to study the physiological processes underlying long-term growth enhancement of heavily thinned Pinus sylvestris in a xeric forest in Switzerland. This approach allowed us to identify and disentangle thinning-induced changes in stomatal conductance and assimilation rate.At our xeric study site, the increase in stomatal conductance far outweighed the increase in assimilation, implying that growth release in heavily thinned trees is primarily driven by enhanced water availability rather than increased light availability.We conclude that in forests with relatively isohydric species (drought avoiders) that are growing close to their physiological limits, thinning is recommended to maintain a less negative water balance and thus foster tree growth, and ultimately the survival of forest trees under drought.

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confidence: 75%

Improvement of water and light availability after thinning at a xeric site: which matters more? A dual isotope approach

et al. 2015

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“…However, the isotope signature of phytoliths formed at 40 % RH suggests a forming water more evaporated than the bulk leaf water. The Péclet effect, which is known to scale with transpiration (e.g., Barnard et al, 2007), can explain this discrepancy. Advection of less evaporated stem water may decrease δ 18 O LW and increase 17 O-excess LW relative to δ 18 O and 17 O-excess of the epidermal water prone to evaporation and from which phytoliths formed.…”

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

confidence: 99%

“…There are multiple ways to reconstruct past continental temperature and precipitation, for instance from pollen (Bartlein et al, 2010;Herbert and Harrison, 2016;Wahl et al, 2012) or tree ring data (Labuhn et al, 2016;Lavergne et al, 2017). However, there is a serious lack of proxies suitable for reconstructing, in a quantitative way, past variations in continental atmospheric RH.…”

Section: Introductionmentioning

confidence: 99%

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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“…Net CO 2 and H 2 O exchange rates were measured, and stomatal conductance (g s ) was subsequently calculated according to von Caemmerer and Farquhar (1981). Separate values of leaf level assimilation rate (A) and c i /c a were calculated for N and N-1 needles (see Barnard et al 2007 for details), assuming g s and A of N-1 needles to amount to 53 and 61% of N needles (Beadle et al 1985). The projected area of the N and N-1 needles that were inserted in the chamber was determined with a leaf area meter (DT Devices, Cambridge, UK), and threedimensional leaf area was calculated according to Luoma (1997).…”

Section: Needle Gas Exchangementioning

confidence: 99%

Temporal dynamics of the carbon isotope composition in a Pinus sylvestris stand: from newly assimilated organic carbon to respired carbon dioxide

et al. 2008

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The (13)C isotopic signature (C stable isotope ratio; delta(13)C) of CO(2) respired from forest ecosystems and their particular compartments are known to be influenced by temporal changes in environmental conditions affecting C isotope fractionation during photosynthesis. Whereas most studies have assessed temporal variation in delta(13)C of ecosystem-respired CO(2) on a day-to-day scale, not much information is available on its diel dynamics. We investigated environmental and physiological controls over potential temporal changes in delta(13)C of respired CO(2) by following the short-term dynamics of the (13)C signature from newly assimilated organic matter pools in the needles, via phloem-transported organic matter in twigs and trunks, to trunk-, soil- and ecosystem-respired CO(2). We found a strong 24-h periodicity in delta(13)C of organic matter in leaf and twig phloem sap, which was strongly dampened as carbohydrates were transported down the trunk. Periodicity reappeared in the delta(13)C of trunk-respired CO(2), which seemed to originate from apparent respiratory fractionation rather than from changes in delta(13)C of the organic substrate. The diel patterns of delta(13)C in soil-respired CO(2) are partly explained by soil temperature and moisture and are probably due to changes in the relative contribution of heterotrophic and autotrophic CO(2) fluxes to total soil efflux in response to environmental conditions. Our study shows that direct relations between delta(13)C of recent assimilates and respired CO(2) may not be present on a diel time scale, and other factors lead to short-term variations in delta(13)C of ecosystem-emitted CO(2). On the one hand, these variations complicate ecosystem CO(2) flux partitioning, but on the other hand they provide new insights into metabolic processes underlying respiratory CO(2) emission.

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Evaporative enrichment and time lags between δ¹⁸O of leaf water and organic pools in a pine stand

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Cited by 84 publications

References 56 publications

Improvement of water and light availability after thinning at a xeric site: which matters more? A dual isotope approach

Improvement of water and light availability after thinning at a xeric site: which matters more? A dual isotope approach

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

Temporal dynamics of the carbon isotope composition in a Pinus sylvestris stand: from newly assimilated organic carbon to respired carbon dioxide

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Evaporative enrichment and time lags between δ18O of leaf water and organic pools in a pine stand

Abstract: ABSTRACT

Cited by 84 publications

References 56 publications

Improvement of water and light availability after thinning at a xeric site: which matters more? A dual isotope approach

Improvement of water and light availability after thinning at a xeric site: which matters more? A dual isotope approach

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

Temporal dynamics of the carbon isotope composition in a Pinus sylvestris stand: from newly assimilated organic carbon to respired carbon dioxide

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Evaporative enrichment and time lags between δ¹⁸O of leaf water and organic pools in a pine stand