scholarly journals Leaf scale quantification of the effect of photosynthetic gas exchange on Δ47 of CO2

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Getachew Agmuas Adnew ◽  
Magdalena E. G. Hofmann ◽  
Thijs L. Pons ◽  
Gerbrand Koren ◽  
Martin Ziegler ◽  
...  
Keyword(s):  
Gas Exchange ◽  
Isotope Composition ◽  
Diffusion Flux ◽  
Leaf Water ◽  
Back Diffusion ◽  
Ambient Conditions ◽  
Photosynthetic Gas Exchange ◽  
O Isotope ◽  
Clumped Isotope ◽  
Kinetic Fractionation

AbstractThe clumped isotope composition (Δ47, the anomaly of the mass 47 isotopologue relative to the abundance expected from a random isotope distribution) of CO2 has been suggested as an additional tracer for gross CO2 fluxes. However, the effect of photosynthetic gas exchange on Δ47 has not been directly determined and two indirect/conceptual studies reported contradicting results. In this study, we quantify the effect of photosynthetic gas exchange on Δ47 of CO2 using leaf cuvette experiments with one C4 and two C3 plants. The experimental results are supported by calculations with a leaf cuvette model. Our results demonstrate the important roles of the Δ47 value of CO2 entering the leaf, kinetic fractionation as CO2 diffuses into, and out of the leaf and CO2–H2O isotope exchange with leaf water. We experimentally confirm the previously suggested dependence of Δ47 of CO2 in the air surrounding a leaf on the stomatal conductance and back-diffusion flux. Gas exchange can enrich or deplete the Δ47 of CO2 depending on the Δ47 of CO2 entering the leaf and the fraction of CO2 exchanged with leaf water and diffused back to the atmosphere, but under typical ambient conditions, it will lead to a decrease in Δ47.

Fractionation of clumped isotopes of CO2 during photosynthesis

2021 ◽  
Author(s):  
Getachew A. Adnew ◽  
Magdalena E.G. Hofmann ◽  
Thijs L. Pons ◽  
Gerbrand Koren ◽  
Martin Ziegler ◽  
...  
Keyword(s):  
Gas Exchange ◽  
Carbon Cycle ◽  
Isotope Composition ◽  
Diffusion Flux ◽  
Carbonic Anhydrase Activity ◽  
Clumped Isotopes ◽  
Photosynthetic Gas Exchange ◽  
O Isotope ◽  
Clumped Isotope ◽  
Kinetic Fractionation

<p>Stable isotope (δ<sup>13</sup>C and δ<sup>18</sup>O) and mole fraction measurements of CO<sub>2</sub> are used to constrain the carbon cycle. However, the gross fluxes of the carbon cycle, especially photosynthesis and respiration, remain uncertain due to the challenging task of distinguishing individual flux terms from each other. The clumped isotope composition (Δ<sub>47</sub>) of CO<sub>2</sub> has been suggested as an additional tracer for gross CO<sub>2</sub> fluxes since it depends mainly on temperature but not on the bulk isotopic composition of leaf, soil and surface water, unlike δ<sup>18</sup>O of CO<sub>2</sub>.</p><p>In this study, we quantify the effect of photosynthetic gas exchange on Δ<sub>47</sub> of CO<sub>2</sub> using leaf cuvette experiments with two C<sub>3</sub> and one C<sub>4</sub> plants and discuss challenges and possible applications of clumped isotope measurements. The experimental results are supported by calculations with a leaf cuvette model. Our results demonstrate how the effect of gas exchange on Δ<sub>47</sub> is controlled by CO<sub>2</sub>-H<sub>2</sub>O isotope exchange (using plants with different carbonic anhydrase activity), and kinetic fractionation as CO<sub>2</sub> diffuses into and out of the leaf (using plants with different stomatal and mesophyll conductance). We experimentally confirm the previously suggested dependence of Δ<sub>47</sub>­­ on the stomatal conductance and back-diffusion flux.</p>

scholarly journals Leaf-scale quantification of the effect of photosynthetic gas exchange on Δ<sup>17</sup>O of atmospheric CO<sub>2</sub>

2020 ◽  
Vol 17 (14) ◽  
pp. 3903-3922
Author(s):  
Getachew Agmuas Adnew ◽  
Thijs L. Pons ◽  
Gerbrand Koren ◽  
Wouter Peters ◽  
Thomas Röckmann
Keyword(s):  
Gas Exchange ◽  
Oxygen Isotope ◽  
Isotope Composition ◽  
Diffusion Flux ◽  
Leaf Water ◽  
Atmospheric Co2 ◽  
C3 Plants ◽  
Back Diffusion ◽  
Photosynthetic Gas Exchange ◽  
Oxygen Isotope Exchange

Abstract. Understanding the processes that affect the triple oxygen isotope composition of atmospheric CO2 during gas exchange can help constrain the interaction and fluxes between the atmosphere and the biosphere. We conducted leaf cuvette experiments under controlled conditions using three plant species. The experiments were conducted at two different light intensities and using CO2 with different Δ17O. We directly quantify the effect of photosynthesis on Δ17O of atmospheric CO2 for the first time. Our results demonstrate the established theory for δ18O is applicable to Δ17O(CO2) at leaf level, and we confirm that the following two key factors determine the effect of photosynthetic gas exchange on the Δ17O of atmospheric CO2. The relative difference between Δ17O of the CO2 entering the leaf and the CO2 in equilibrium with leaf water and the back-diffusion flux of CO2 from the leaf to the atmosphere, which can be quantified by the cm∕ca ratio, where ca is the CO2 mole fraction in the surrounding air and cm is the one at the site of oxygen isotope exchange between CO2 and H2O. At low cm∕ca ratios the discrimination is governed mainly by diffusion into the leaf, and at high cm∕ca ratios it is governed by back-diffusion of CO2 that has equilibrated with the leaf water. Plants with a higher cm∕ca ratio modify the Δ17O of atmospheric CO2 more strongly than plants with a lower cm∕ca ratio. Based on the leaf cuvette experiments, the global value for discrimination against Δ17O of atmospheric CO2 during photosynthetic gas exchange is estimated to be -0.57±0.14 ‰ using cm∕ca values of 0.3 and 0.7 for C4 and C3 plants, respectively. The main uncertainties in this global estimate arise from variation in cm∕ca ratios among plants and growth conditions.

Leaf-scale quantification of the effect of photosynthetic gas exchange on Δ17O of atmospheric CO2

2020 ◽  
Author(s):  
Getachew Adnew ◽  
Thijs Pons ◽  
Gerbrand Koren ◽  
Wouter Peters ◽  
Thomas Röckmann
Keyword(s):  
Stomatal Conductance ◽  
Gas Exchange ◽  
Photosynthetic Capacity ◽  
Isotope Composition ◽  
Diffusion Flux ◽  
Relative Difference ◽  
Leaf Water ◽  
Back Diffusion ◽  
Photosynthetic Gas Exchange ◽  
High Photosynthetic Capacity

&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Understanding the processes affecting the triple oxygen isotope composition of atmospheric CO&lt;sub&gt;2&lt;/sub&gt; during photosynthesis can help to constrain the interaction and fluxes between the atmosphere and the biosphere. We conducted leaf cuvette experiments under controlled conditions, using sunflower (&lt;em&gt;Helianthus annuus&lt;/em&gt;), an annual C&lt;sub&gt;3&lt;/sub&gt; species with high photosynthetic capacity and stomatal conductance for CO&lt;sub&gt;2&lt;/sub&gt;, an evergreen C&lt;sub&gt;3&lt;/sub&gt; species, ivy (&lt;em&gt;Hedera hybernica&lt;/em&gt;) with lower values for these traits, and a C&lt;sub&gt;4&lt;/sub&gt; species maize (&lt;em&gt;Zea mays)&lt;/em&gt; that has a high photosynthetic capacity and low stomatal conductance. The experiments were conducted at different light intensities and using CO&lt;sub&gt;2&lt;/sub&gt; with different &lt;sup&gt;17&lt;/sup&gt;O- excess. Our results demonstrate that two key factors determine the effect of photosynthetic gas exchange on &amp;#916;&lt;sup&gt;17&lt;/sup&gt;O of atmospheric CO&lt;sub&gt;2&lt;/sub&gt;: The relative difference in &amp;#916;&lt;sup&gt;17&lt;/sup&gt;O of the CO&lt;sub&gt;2&lt;/sub&gt; entering the leaf and &amp;#916;&lt;sup&gt;17&lt;/sup&gt;O of leaf water, and the back-diffusion flux from the leaf to the atmosphere, which can be quantified by the c&lt;sub&gt;m&lt;/sub&gt;/c&lt;sub&gt;a&lt;/sub&gt; ratio.&amp;#160; At low c&lt;sub&gt;m&lt;/sub&gt;/c&lt;sub&gt;a&lt;/sub&gt; the discrimination is governed by diffusion into the leaf, and at high c&lt;sub&gt;m&lt;/sub&gt;/c&lt;sub&gt;a&lt;/sub&gt; by back-diffusion of CO&lt;sub&gt;2&lt;/sub&gt; that has equilibrated with the leaf water. Plants with a higher c&lt;sub&gt;m&lt;/sub&gt;/c&lt;sub&gt;a&lt;/sub&gt; ratio modify the &amp;#916;&lt;sup&gt;17&lt;/sup&gt;O of atmospheric CO&lt;sub&gt;2&lt;/sub&gt; more strongly than plants with lower c&lt;sub&gt;m&lt;/sub&gt;/c&lt;sub&gt;a&lt;/sub&gt;.&amp;#160;&lt;/p&gt;&lt;p&gt;Based on the leaf cuvette experiments using both C&lt;sub&gt;4&lt;/sub&gt; and C&lt;sub&gt;3&lt;/sub&gt; plants, the global discrimination in &lt;sup&gt;17&lt;/sup&gt;O-excess of atmospheric CO&lt;sub&gt;2&lt;/sub&gt; due to assimilation is estimated to be -0.6&amp;#177;0.2&amp;#8240;. The main uncertainty in the global estimation is due to the uncertainty in the c&lt;sub&gt;m&lt;/sub&gt;/c&lt;sub&gt;a&lt;/sub&gt; ratio.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals Leaf-scale quantification of the effect of photosynthetic gas exchange on Δ<sup>17</sup>O of atmospheric CO<sub>2</sub>

2020 ◽  
Author(s):  
Getachew Agmuas Adnew ◽  
Thijs L. Pons ◽  
Gerbrand Koren ◽  
Wouter Peters ◽  
Thomas Röckmann
Keyword(s):  
Gas Exchange ◽  
Oxygen Isotope ◽  
Mole Fraction ◽  
Isotope Composition ◽  
Leaf Water ◽  
Oxygen Isotope Composition ◽  
Atmospheric Co2 ◽  
C3 Plants ◽  
Back Diffusion ◽  
Photosynthetic Gas Exchange

Abstract. Understanding the processes that affect the triple oxygen isotope composition of atmospheric CO2 during gas exchange can help constrain the interaction and fluxes between the atmosphere and the biosphere. We conducted leaf cuvette experiments under controlled conditions, using three plant species. The experiments were conducted at two different light intensities and using CO2 with different 17O-excess. The oxygen isotope composition of CO2 was used to estimate cm, the mole fraction of CO2 at the CO2-H2O exchange site. Our results demonstrate that two key factors determine the effect of gas exchange on the Δ17O of atmospheric CO2. The relative difference between Δ17O of the CO2 entering the leaf and the CO2 in equilibrium with leaf water, and the back-diffusion flux of CO2 from the leaf to the atmosphere, which can be quantified by the cm/ca ratio where ca is the CO2 mole fraction in the surrounding air. At low cm/ca ratio the discrimination is governed mainly by diffusion into the leaf, and at high cm/ca ratio by back-diffusion of CO2 that has equilibrated with the leaf water. Plants with a higher cm/ca ratio modify the Δ17O of atmospheric CO2 more strongly than plants with a lower cm/ca ratio. Based on the leaf cuvette experiments, the global value for discrimination against Δ17O of atmospheric CO2 during the photosynthetic gas exchange is estimated to be −0.57+/−0.14 ‰ using cm/ca values of 0.3 and 0.7 for C4 and C3 plants, respectively. The main uncertainties in this global estimate arise from variation in cm/ca ratios among plants and growth conditions.

Effect of Changes in Leaf Water Oxygen Isotopic Composition on Discrimination Against C18O16O During Photosynthetic Gas Exchange

1994 ◽  
Vol 21 (2) ◽  
pp. 221 ◽  
Author(s):  
LB Flanagan ◽  
SL Phillips ◽  
JR Ehleringer ◽  
J Lloyd ◽  
GD Farquhar
Keyword(s):  
Gas Exchange ◽  
Isotopic Composition ◽  
Vapour Pressure ◽  
Mechanistic Model ◽  
Isotopic Fractionation ◽  
Oxygen Isotopic Composition ◽  
Leaf Water ◽  
Photosynthetic Gas Exchange ◽  
Oxygen Isotopic ◽  
Environment Chamber

Photosynthetic gas exchange measurements were combined with measurements of the carbon and oxygen stable isotopic composition of CO2 after it passed over a leaf of Phaseolus vulgaris or Senecio spp. plants held in a controlled environment chamber. Calculations were then made of discrimination by the leaf against 13CO2 and C18O16O. Leaves were maintained at different vapour pressure gradients in order to generate a range of leaf water 18CO/16CO ratios. The 18CO content of leaf water increased when plants were exposed to higher vapour pressure deficits. The observed C18O16O discrimination values also increased with an increase in the leaf-air vapour pressure gradient and the associated change in leaf water 18/CO16CO values. In addition, the observed C18O16O discrimination values were strongly correlated with values predicted by a mechanistic model of isotopic fractionation.

scholarly journals Where in the leaf is intercellular CO2 (Ci)? Considerations and recommendations for assessing gaseous diffusion in leaves

2020 ◽  
Author(s):  
Joseph R. Stinziano ◽  
Jun Tominaga ◽  
David T. Hanson
Keyword(s):  
Water Vapor ◽  
High Temperature ◽  
Stomatal Conductance ◽  
Gas Exchange ◽  
Water Loss ◽  
Leaf Water ◽  
Marginal Effect ◽  
Photosynthetic Gas Exchange ◽  
Gaseous Diffusion ◽  
Intercellular Co2

AbstractThe assumptions that water vapor exchange occurs exclusively through stomata, that the intercellular airspace is fully saturated with water vapor, and that CO2 gradients are negligible between stomata and the intercellular airspace have enabled significant advancements in photosynthetic gas exchange research for nearly 60 years via calculation of intercellular CO2 (Ci). However, available evidence suggests that these assumptions may be overused. Here we review the literature surrounding evidence for and against the assumptions made by Moss & Rawlins (1963). We reinterpret data from the literature by propagating different rates of cuticular water loss, CO2 gradients, and unsaturation through the data. We find that in general, when cuticle conductance is less than 1% of stomatal conductance, the assumption that water vapor exchange occurs exclusively through stomata has a marginal effect on gas exchange calculations, but this is not true when cuticle conductance exceeds 5% of stomatal conductance. Our analyses further suggest that CO2 and water vapor gradients have stronger impacts at higher stomatal conductance, while cuticle conductance has a greater impact at lower stomatal conductance. Therefore, we recommend directly measuring Ci whenever possible, measuring apoplastic water potentials to estimate humidity inside the leaf, and exercising caution when interpreting data under conditions of high temperature and/or low stomatal conductance, and when a species is known to have high cuticular conductance.HighlightLeaf water vapor and CO2 exchange have been successfully used to model photosynthetic biochemistry. We review critical assumptions in these models and make recommendations about which need to be re-assessed.

Combined clumped isotope measurements resolve kinetic biases in carbonate formation temperatures

2020 ◽  
Author(s):  
David Bajnai ◽  
Weifu Guo ◽  
Niklas Löffler ◽  
Katharina Methner ◽  
Emilija Krsnik ◽  
...  
Keyword(s):  
High Precision ◽  
Dissolved Inorganic Carbon ◽  
Isotope Composition ◽  
Coral Skeletons ◽  
Carbonate Formation ◽  
Devils Hole ◽  
Kinetic Effects ◽  
Clumped Isotope ◽  
Kinetic Fractionation ◽  
Geologic Record

&lt;p&gt;Reaction kinetics involved in the precipitation of carbonates can introduce large scatter and inaccuracies in the temperatures derived from their &lt;em&gt;&amp;#948;&lt;/em&gt;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#8710;&lt;sub&gt;47&lt;/sub&gt; values. Advances in mass spectrometry instrumentation recently enabled high-precision analysis of the &lt;sup&gt;18&lt;/sup&gt;O&amp;#8211;&lt;sup&gt;18&lt;/sup&gt;O clumping in carbonate minerals (&lt;em&gt;&amp;#8710;&lt;/em&gt;&lt;sub&gt;48&lt;/sub&gt;), despite the relatively low natural abundance of &lt;sup&gt;12&lt;/sup&gt;C&lt;sup&gt;18&lt;/sup&gt;O&lt;sup&gt;18&lt;/sup&gt;O, the main isotopologue contributing to the &lt;em&gt;&amp;#8710;&lt;/em&gt;&lt;sub&gt;48&lt;/sub&gt;&amp;#160;signal (1). Measurements of &lt;em&gt;&amp;#8710;&lt;/em&gt;&lt;sub&gt;48&lt;/sub&gt;, when combined with &lt;em&gt;&amp;#8710;&lt;/em&gt;&lt;sub&gt;47,&lt;/sub&gt; can yield additional insights into kinetic effects and the carbonate formation environment (2).&lt;/p&gt;&lt;p&gt;Here we report high-precision &lt;em&gt;&amp;#8710;&lt;/em&gt;&lt;sub&gt;47&lt;/sub&gt; and &lt;em&gt;&amp;#8710;&lt;/em&gt;&lt;sub&gt;48&lt;/sub&gt; values of speleothem carbonates, modern coral skeletons, a brachiopod, and a belemnite. We constrained equilibrium in &lt;em&gt;&amp;#8710;&lt;/em&gt;&lt;sub&gt;47&lt;/sub&gt; vs &lt;em&gt;&amp;#8710;&lt;/em&gt;&lt;sub&gt;48&lt;/sub&gt; space by anchoring empirically derived &lt;em&gt;&amp;#8710;&lt;/em&gt;&lt;sub&gt;47&lt;/sub&gt; vs temperature and &lt;em&gt;&amp;#8710;&lt;/em&gt;&lt;sub&gt;48&lt;/sub&gt; vs temperature relationships to a Devils Hole mammillary calcite, known to be precipitated at extremely slow rates at a constant 33.7(&amp;#177;0.8)&amp;#160;&amp;#176;C and water oxygen isotope composition. Our results, compared to theoretical predictions, provide the most substantial evidence to date that the isotopic disequilibrium commonly observed in speleothems and scleractinian coral skeletons is inherited from the dissolved inorganic carbon pool of their parent solutions. Data from an ancient belemnite imply it precipitated near isotopic equilibrium and confirm the warmer-than-present temperatures at Early Cretaceous southern high latitudes. The presence of similar kinetic departure in a brachiopod but not in a belemnite suggests that the current discrepancy between belemnite and brachiopod-based temperature estimates in the geologic record is most likely related to a greater kinetic bias in the isotopic composition of brachiopod shells.&lt;/p&gt;&lt;p&gt;We demonstrate that the combined clumped isotope method makes it possible to identify carbonates that did not precipitate in thermodynamic equilibrium from their parent water. Our results highlight the potential that the combined clumped isotope analyses hold for accurate paleoclimate reconstructions and the identification of the kinetic fractionation processes dominant in carbonate (bio)mineralisation.&lt;/p&gt;&lt;p&gt;(1) Fiebig et al. (2019), https://doi.org/10.1016/j.chemgeo.2019.05.019&lt;/p&gt;&lt;p&gt;(2) Guo, W. (2020), https://doi.org/10.1016/j.gca.2019.07.055&lt;/p&gt;

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