The contribution of photosynthesis and soil respiration to net land-atmosphere carbon dioxide (CO... more The contribution of photosynthesis and soil respiration to net land-atmosphere carbon dioxide (CO<sub>2</sub>) exchange can be estimated based on the differential influence of leaves and soils on budgets of the oxygen isotope composition (δ<sup>18</sup>O) of atmospheric CO<sub>2</sub>. To do so, the activity of carbonic anhydrases (CA), a group of enzymes that catalyse the hydration of CO<sub>2</sub>, in soils and plants needs to be understood. Measurements of soil CA activity typically involve the inversion of models describing the δ<sup>18</sup>O of CO<sub>2</sub> fluxes to solve for the apparent, potentially catalysed, rate of CO<sub>2</sub> hydration. This requires information about the…
Estimates of photosynthetic and respiratory fluxes at large scales is needed to improve our predi... more Estimates of photosynthetic and respiratory fluxes at large scales is needed to improve our predictions of the current and future global CO<sub>2</sub> cycle. Carbonyl sulphide (OCS) is the most abundant sulphur gas in the atmosphere and has been proposed as a new tracer of photosynthesis (GPP), as the uptake of OCS from the atmosphere is dominated by the activity of carbonic anhydrase (CA), an enzyme abundant in leaves that also catalyses CO<sub>2</sub> hydration during photosynthesis. But soils also exchange OCS with the atmosphere which complicates the retrieval of GPP from atmospheric budgets. Indeed soils can take up large amounts of OCS from the atmosphere as soil microorganisms also contain CA, and OCS emissions from soils have been reported in agricultural fields or anoxic soils. To date no mechanistic framework exists to describe this exchange of OCS between soils and the atmosphere but empirical results, once upscaled to the global scale, indicate t...
ABSTRACT Stable isotopes in tree-rings are widely used for the reconstruction of environmental co... more ABSTRACT Stable isotopes in tree-rings are widely used for the reconstruction of environmental conditions, but more information could be extracted when using mechanistic models for their interpretation. Tree-ring width, cell wall structure and stable carbon as well as oxygen isotope analyses in tree wood and cellulose were carried out for four larch trees (Larix cajanderi Mayr) from northeastern Yakutia (69°N, 148°E) during the period from 1945 to 2004 and these data compared with several models. Based on a biochemical model of photosynthesis and modified model of stomatal conductance our work provides intra-annual dynamics of carbon content in photoassimilates and isotope composition in tree-rings depending on climatic factors. The mechanistic Roden-Lin-Ehleringer model was used to quantify both the physical and biochemical fractionation events associated with hydrogen and oxygen isotope ratios in tree-ring cellulose. Simulation results were compared with measured data. Predictions of carbon isotope ratios from Fritts, ORCHIDEE and LPX models were consistent with measured data. The Roden-Lin-Ehleringer oxygen model allowed the prediction of humidity and source water enrichment as well as oxygen isotope effects associated with leaf water enrichment. This work was supported by Marie Curie Fellowships (EU-ISOTREC 235122; 909122) awarded to Sidorova Olga and a grant of Russian Scientific School 5327.2012.4.
The contribution of photosynthesis and soil respiration to net land-atmosphere carbon dioxide (CO... more The contribution of photosynthesis and soil respiration to net land-atmosphere carbon dioxide (CO<sub>2</sub>) exchange can be estimated based on the differential influence of leaves and soils on budgets of the oxygen isotope composition (δ<sup>18</sup>O) of atmospheric CO<sub>2</sub>. To do so, the activity of carbonic anhydrases (CA), a group of enzymes that catalyse the hydration of CO<sub>2</sub>, in soils and plants needs to be understood. Measurements of soil CA activity typically involve the inversion of models describing the δ<sup>18</sup>O of CO<sub>2</sub> fluxes to solve for the apparent, potentially catalysed, rate of CO<sub>2</sub> hydration. This requires information about the…
Estimates of photosynthetic and respiratory fluxes at large scales is needed to improve our predi... more Estimates of photosynthetic and respiratory fluxes at large scales is needed to improve our predictions of the current and future global CO<sub>2</sub> cycle. Carbonyl sulphide (OCS) is the most abundant sulphur gas in the atmosphere and has been proposed as a new tracer of photosynthesis (GPP), as the uptake of OCS from the atmosphere is dominated by the activity of carbonic anhydrase (CA), an enzyme abundant in leaves that also catalyses CO<sub>2</sub> hydration during photosynthesis. But soils also exchange OCS with the atmosphere which complicates the retrieval of GPP from atmospheric budgets. Indeed soils can take up large amounts of OCS from the atmosphere as soil microorganisms also contain CA, and OCS emissions from soils have been reported in agricultural fields or anoxic soils. To date no mechanistic framework exists to describe this exchange of OCS between soils and the atmosphere but empirical results, once upscaled to the global scale, indicate t...
ABSTRACT Stable isotopes in tree-rings are widely used for the reconstruction of environmental co... more ABSTRACT Stable isotopes in tree-rings are widely used for the reconstruction of environmental conditions, but more information could be extracted when using mechanistic models for their interpretation. Tree-ring width, cell wall structure and stable carbon as well as oxygen isotope analyses in tree wood and cellulose were carried out for four larch trees (Larix cajanderi Mayr) from northeastern Yakutia (69°N, 148°E) during the period from 1945 to 2004 and these data compared with several models. Based on a biochemical model of photosynthesis and modified model of stomatal conductance our work provides intra-annual dynamics of carbon content in photoassimilates and isotope composition in tree-rings depending on climatic factors. The mechanistic Roden-Lin-Ehleringer model was used to quantify both the physical and biochemical fractionation events associated with hydrogen and oxygen isotope ratios in tree-ring cellulose. Simulation results were compared with measured data. Predictions of carbon isotope ratios from Fritts, ORCHIDEE and LPX models were consistent with measured data. The Roden-Lin-Ehleringer oxygen model allowed the prediction of humidity and source water enrichment as well as oxygen isotope effects associated with leaf water enrichment. This work was supported by Marie Curie Fellowships (EU-ISOTREC 235122; 909122) awarded to Sidorova Olga and a grant of Russian Scientific School 5327.2012.4.
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Papers by Thomas Launois