Graham Farquhar - Profile on Academia.edu (original) (raw)
Papers by Graham Farquhar
Silva Fennica, 2002
We develop, and discuss the implementation of, a mathematical framework for inferring optimal pat... more We develop, and discuss the implementation of, a mathematical framework for inferring optimal patterns of water and nitrogen use. Our analysis is limited to a time scale of one day and a spatial scale consisting of the green canopy of one plant, and we assume that this canopy has fi xed quantities of nitrogen and water available for use in photosynthesis. The effi ciencies of water and nitrogen use, and the interactions between the two, are strongly affected by physiological and physical properties that can be modeled in different ways. The thrust of this study is therefore to discuss these properties and how they affect the effi ciencies of nitrogen and water use, and to demonstrate, qualitatively, the effects of different model assumptions on inferred optimal strategies. Preliminary simulations suggest that the linked optimisation of nitrogen and water use is particularly sensitive to the level of detail in canopy light penetration models (e.g., whether sunlit and shaded fractions are pooled or considered independently), and to assumptions regarding nitrogen and irradiance gradients within leaves (which determine how whole-leaf potential electron transport rate is calculated from leaf nitrogen content and incident irradiance).
Silva Fennica, 2002
We introduce the simultaneous optimisation of water-use effi ciency and nitrogen-use effi ciency ... more We introduce the simultaneous optimisation of water-use effi ciency and nitrogen-use effi ciency of canopy photosynthesis. As a vehicle for this idea we consider the optimal leaf area for a plant in which there is no self-shading among leaves. An emergent result is that canopy assimilation over a day is a scaled sum of daily water use and of photosynthetic nitrogen display. The respective scaling factors are the marginal carbon benefi ts of extra transpiration and extra such nitrogen, respectively. The simple approach successfully predicts that as available water increases, or evaporative demand decreases, the leaf area should increase, with a concomitant reduction in nitrogen per unit leaf area. The changes in stomatal conductance are therefore less than would occur if leaf area were not to change. As irradiance increases, the modelled leaf area decreases, and nitrogen/leaf area increases. As total available nitrogen increases, leaf area also increases. In all the examples examined, the sharing by leaf area and properties per unit leaf area means that predicted changes in either are less than if predicted in isolation. We suggest that were plant density to be included, it too would further share the response, further diminishing the changes required per unit leaf area.
Measurement of guard cell wall elasticity and implications for stomatal sensitivity to environmental stimuli
Science Access, 2001
Over the course of stomatal opening guard cells exhibit dramatic changes in volume. This dynamic ... more Over the course of stomatal opening guard cells exhibit dramatic changes in volume. This dynamic characteristic is driven by changes in guard cell osmotic pressure and water potential, but constrained by the elastic properties of the guard cell walls. Thus guard cell wall elasticity will strongly influence the sensitivity of stomata to environmental stimuli. However, our understanding of guard cell wall elastic properties is limited. In this study we calculated the elastic modulus e of guard cells of Vicia faba L. by taking concurrent measurements of guard cell volume and pressure using confocal microscopy and a cell pressure probe. While controlling guard cell pressure at intervals over the range 0.3 to 5.0 MPa, guard cell volume increased with pressure in a saturating fashion and e increased linearly from approximately 2 to 40 MPa. These new data allow a quantitative understanding of the relationship between guard cell osmotic content and stomatal conductance, with implications fo...
Changes of the variances of global precipitation based on the IPCC AR4 Climate Models
AGU Fall Meeting Abstracts, Dec 1, 2009
In the Chapter 11 of the IPCC AR4, Christensen et al. (2007) state ``warming generally increases ... more In the Chapter 11 of the IPCC AR4, Christensen et al. (2007) state ``warming generally increases the spatial variability of precipitation, contributing to a reduction of rainfall in the subtropics and an increase at higher latitudes and in parts of the tropics.'' In the meantime, Held and Soden (2006, Figure 9) using the zonal-mean variance of monthly mean anomalies in
Crop Science, 1992
Breeding cultivars with improved water use efficiency (WUE = total biomass production/water use) ... more Breeding cultivars with improved water use efficiency (WUE = total biomass production/water use) has been limited by the lack of suitable screening criteria. Theory has predicted an association between WUE and Δ (leaf discrimination against 13C) that could be used in indirect selection for WUE in C3 plants. Several studies have provided empirical evidence supporting this theory but with some exceptions. Earlier studies showed genotypic and drought‐induced variation in Δ in cowpea (Vigna unguiculata (L.) Walp.) and expected associations with leaf gas exchange for drought‐induced effects but not for genotypic effects. Studies were conducted to evaluate directly the association between seasonal WUE and Δ in cowpea. Five contrasting genotypes and two isogenic lines were grown in the field either in pots or under natural soil conditions and subjected to well‐watered or drought treatments. Genotypic rankings for Δ in leaves were consistent in the wet and dry pot and natural soil condition...
Annals of Applied Biology, Apr 1, 1993
Crop growth, water-use efficiency and carbon isotope discrimination in groundnut (Amchis hypogaea... more Crop growth, water-use efficiency and carbon isotope discrimination in groundnut (Amchis hypogaea L.) genotypes under endsf season drought conditions*
Carbon Isotope Fractionation and Plant Water-Use Efficiency
Springer eBooks, 1989
ABSTRACT
Carbon Isotope Discrimination Varies Genetically in C4 Species
Plant Physiology, Feb 1, 1990
Australian journal of agricultural research, 1991
Pod yield response of two spanish (McCubbin and Red Spanish) and two virginia (Virginia Bunch and... more Pod yield response of two spanish (McCubbin and Red Spanish) and two virginia (Virginia Bunch and Q18801) cultivars were compared under a range of irrigation treatments applied at different growth stages on a Xanthozem soil in a subtropical environment in southeast Queensland. Detailed growth and soil water use measurements were taken on a fully irrigated treatment and a treatment which received no rainfall after 83 days after planting (DAP). Soil water deficits occurring during the flowering to the start of pod growth phase (R/I) significantly reduced pod yields (range, 17-25%) relative to the well-watered control plots (I/I) for all cultivars. Where crops were irrigated until 8 3 DAP, then crop water deficits occurred throughout the pod growth phase (I/R), a significant cultivar by irrigation treatment interaction was observed for pod yield. The greatest reduction in yield occurred when severe stress occurred during the pod filling phase (Sh). Significant cultivar variation in pod yield was apparent. Differences in pod yield within this treatment were analysed in terms of a simple framework where pod yield is a function of transpired water (T) , transpiration efficiency (TE) and harvest index (H). Estimates of TE derived from measurements of carbon isotope discrimination in leaves indicated only small variation in TE, and suggest this trait contributed little to pod yield variation in the cultivars used in this experiment. Variation in pod yield among the four cultivars was largely a result of differences in harvest index characteristics.
Annual review of plant physiology and plant molecular biology, Jun 1, 1989
Correlation between the Carbon Isotope Discrimination in Leaf Starch and Sugars of C3 Plants and the Ratio of Intercellular and Atmospheric Partial Pressures of Carbon Dioxide
Plant Physiology, Dec 1, 1988
Photosynthesis and gas exchange
Cambridge University Press eBooks, Oct 27, 1989
Nature, Sep 1, 1993
LETTERS TO NATURE second step reaction of group I introns). We propose that the spliceosome gener... more LETTERS TO NATURE second step reaction of group I introns). We propose that the spliceosome generates a group I-like catalytic site to execute the second step of pre-mRNA splicing. D
Photosynthetic manipulation provides new opportunities for enhancing crop yield. However, underst... more Photosynthetic manipulation provides new opportunities for enhancing crop yield. However, understanding and quantifying effectively how the seasonal growth and yield dynamics of target crops might be affected over a wide range of environments is limited. Using a state-of-the-art cross-scale model we predicted crop-level impacts of a broad list of promising photosynthesis manipulation strategies for C3 wheat and C4 sorghum. The manipulation targets have varying effects on the enzyme-limited (Ac) and electron transport-limited (Aj) rates of photosynthesis. In the top decile of seasonal outcomes, yield gains with the list of manipulations were predicted to be modest, ranging between 0 and 8%, depending on the crop type and manipulation. To achieve the higher yield gains, large increases in both Ac and Aj are needed. This could likely be achieved by stacking Rubisco function and electron transport chain enhancements or installing a full CO2 concentrating system. However, photosynthetic ...
Nature Plants, 2020
Stable isotopes are commonly used to study the diffusion of CO inside photosynthetic tissues of p... more Stable isotopes are commonly used to study the diffusion of CO inside photosynthetic tissues of plants. The standard method to interpret the observed preference for the lighter carbon isotope in C 3 photosynthesis involves the model by Farquhar, O'Leary and Berry, which relates carbon isotope discrimination to physical and biochemical processes inside the leaf. However, under many conditions the model returns unreasonable results for mesophyll conductance to CO 2 diffusion (g m), especially when rates of photosynthesis are low. Here we re-derive the carbon isotope discrimination model using modified assumptions related to the isotope effect of mitochondrial respiration. In particular, we treat the carbon pool associated with respiration as separate from the pool of the primary assimilates. We experimentally test the model by comparing g m values measured with different CO 2 source gases varying in their isotopic composition and show that our new model returns matching g m values that are much more reasonable than those obtained with the old model. We use our results to discuss CO 2 diffusion properties inside the mesophyll.
Functional Plant Biology, 2019
Rice quantitative trait locus (QTL) qDTY12.1 is a major-effect drought yield QTL that was identif... more Rice quantitative trait locus (QTL) qDTY12.1 is a major-effect drought yield QTL that was identified from a cross of Vandana (recipient parent) and Way Rarem (donor parent) through breeding efforts to improve rice yield under upland drought stress conditions. The two main physiological effects previously observed to be related to the presence of qDTY12.1 were (i) increased lateral root growth, and (ii) increased transpiration efficiency. Since relatively more progress has thus far been made on characterising the lateral root growth response related to qDTY12.1, the present study focussed on characterising how qDTY12.1 confers higher transpiration efficiency under upland drought stress in the Vandana background. In a series of field experiments in which stomatal conductance was measured across different times of day in four qDTY12.1 near isogenic lines (NILs), the NILs and Way Rarem showed consistently higher stomatal conductance than Vandana under conditions of low vapour pressure d...
Functional Plant Biology, 2018
Photosynthetic manipulation is seen as a promising avenue for advancing field crop productivity. ... more Photosynthetic manipulation is seen as a promising avenue for advancing field crop productivity. However, progress is constrained by the lack of connection between leaf-level photosynthetic manipulation and crop performance. Here we report on the development of a model of diurnal canopy photosynthesis for well watered conditions by using biochemical models of C3 and C4 photosynthesis upscaled to the canopy level using the simple and robust sun–shade leaves representation of the canopy. The canopy model was integrated over the time course of the day for diurnal canopy photosynthesis simulation. Rationality analysis of the model showed that it simulated the expected responses in diurnal canopy photosynthesis and daily biomass accumulation to key environmental factors (i.e. radiation, temperature and CO2), canopy attributes (e.g. leaf area index and leaf angle) and canopy nitrogen status (i.e. specific leaf nitrogen and its profile through the canopy). This Diurnal Canopy Photosynthesi...
Plant Physiology, 1997
Cuticular properties affect the gas exchange of leaves, but little is known about how much CO2 an... more Cuticular properties affect the gas exchange of leaves, but little is known about how much CO2 and water vapor cross the cuticular barrier or whether low water potentials affect the process. Therefore, we measured the cuticular conductances for CO2 and water vapor in grape (Vitis vinifera L.) leaves having various water potentials. The lower leaf surface was sealed to force all gas exchange through the upper surface, which was stoma-free. In this condition both gases passed through the cuticle, and the CO2 conductance could be directly determined from the internal mole fraction of CO2 near the compensation point, the external mole fraction of CO2, and the CO2 flux. The cuticle allowed small amounts of CO2 and water vapor to pass through, indicating that gas exchange occurs in grape leaves no matter how tightly the stomata are closed. However, the CO2 conductance was only 5.7% of that for water vapor. This discrimination against CO2 markedly affected calculations of the mole fraction...
New Phytologist, 2015
Summary Leaf dark respiration (Rdark) is an important yet poorly quantified component of the glob... more Summary Leaf dark respiration (Rdark) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of Rdark and associated leaf traits. Data for 899 species were compiled from 100 sites (from the Arctic to the tropics). Several woody and nonwoody plant functional types (PFTs) were represented. Mixed‐effects models were used to disentangle sources of variation in Rdark. Area‐based Rdark at the prevailing average daily growth temperature (T) of each site increased only twofold from the Arctic to the tropics, despite a 20°C increase in growing T (8–28°C). By contrast, Rdark at a standard T (25°C, Rdark25) was threefold higher in the Arctic than in the tropics, and twofold higher at arid than at mesic sites. Species and PFTs at cold sites exhibited higher Rdark25 at a given photosynthetic capacity (Vcmax25) or leaf nitrogen concentration ([N]) than species at warmer sites. Rdark25 values at any given Vcmax25 or [N] were higher...
Genetic Variation in the Relationship between Photosynthetic CO2 Assimilation Rate and Stomatal Conductance to Water Loss
Progress in Photosynthesis Research, 1987
Jones (1) has discussed two main reasons for attempting to manipulate stornata by breeding. The f... more Jones (1) has discussed two main reasons for attempting to manipulate stornata by breeding. The first was to maximise productivity and hence yield, by increasing rates of assimilation of CO2. An increase in stomatal conductance would be expected to achieve this in C3 species by increasing the partial pressure of CO2 within the leaf, p., which would be useful in conditions where water supply is not limiting. The second was to improve drought tolerance. A decreased stomatal conductance can aid in this direction, but at some expense to yield potential (yield in well-watered conditions).
Silva Fennica, 2002
We develop, and discuss the implementation of, a mathematical framework for inferring optimal pat... more We develop, and discuss the implementation of, a mathematical framework for inferring optimal patterns of water and nitrogen use. Our analysis is limited to a time scale of one day and a spatial scale consisting of the green canopy of one plant, and we assume that this canopy has fi xed quantities of nitrogen and water available for use in photosynthesis. The effi ciencies of water and nitrogen use, and the interactions between the two, are strongly affected by physiological and physical properties that can be modeled in different ways. The thrust of this study is therefore to discuss these properties and how they affect the effi ciencies of nitrogen and water use, and to demonstrate, qualitatively, the effects of different model assumptions on inferred optimal strategies. Preliminary simulations suggest that the linked optimisation of nitrogen and water use is particularly sensitive to the level of detail in canopy light penetration models (e.g., whether sunlit and shaded fractions are pooled or considered independently), and to assumptions regarding nitrogen and irradiance gradients within leaves (which determine how whole-leaf potential electron transport rate is calculated from leaf nitrogen content and incident irradiance).
Silva Fennica, 2002
We introduce the simultaneous optimisation of water-use effi ciency and nitrogen-use effi ciency ... more We introduce the simultaneous optimisation of water-use effi ciency and nitrogen-use effi ciency of canopy photosynthesis. As a vehicle for this idea we consider the optimal leaf area for a plant in which there is no self-shading among leaves. An emergent result is that canopy assimilation over a day is a scaled sum of daily water use and of photosynthetic nitrogen display. The respective scaling factors are the marginal carbon benefi ts of extra transpiration and extra such nitrogen, respectively. The simple approach successfully predicts that as available water increases, or evaporative demand decreases, the leaf area should increase, with a concomitant reduction in nitrogen per unit leaf area. The changes in stomatal conductance are therefore less than would occur if leaf area were not to change. As irradiance increases, the modelled leaf area decreases, and nitrogen/leaf area increases. As total available nitrogen increases, leaf area also increases. In all the examples examined, the sharing by leaf area and properties per unit leaf area means that predicted changes in either are less than if predicted in isolation. We suggest that were plant density to be included, it too would further share the response, further diminishing the changes required per unit leaf area.
Measurement of guard cell wall elasticity and implications for stomatal sensitivity to environmental stimuli
Science Access, 2001
Over the course of stomatal opening guard cells exhibit dramatic changes in volume. This dynamic ... more Over the course of stomatal opening guard cells exhibit dramatic changes in volume. This dynamic characteristic is driven by changes in guard cell osmotic pressure and water potential, but constrained by the elastic properties of the guard cell walls. Thus guard cell wall elasticity will strongly influence the sensitivity of stomata to environmental stimuli. However, our understanding of guard cell wall elastic properties is limited. In this study we calculated the elastic modulus e of guard cells of Vicia faba L. by taking concurrent measurements of guard cell volume and pressure using confocal microscopy and a cell pressure probe. While controlling guard cell pressure at intervals over the range 0.3 to 5.0 MPa, guard cell volume increased with pressure in a saturating fashion and e increased linearly from approximately 2 to 40 MPa. These new data allow a quantitative understanding of the relationship between guard cell osmotic content and stomatal conductance, with implications fo...
Changes of the variances of global precipitation based on the IPCC AR4 Climate Models
AGU Fall Meeting Abstracts, Dec 1, 2009
In the Chapter 11 of the IPCC AR4, Christensen et al. (2007) state ``warming generally increases ... more In the Chapter 11 of the IPCC AR4, Christensen et al. (2007) state ``warming generally increases the spatial variability of precipitation, contributing to a reduction of rainfall in the subtropics and an increase at higher latitudes and in parts of the tropics.'' In the meantime, Held and Soden (2006, Figure 9) using the zonal-mean variance of monthly mean anomalies in
Crop Science, 1992
Breeding cultivars with improved water use efficiency (WUE = total biomass production/water use) ... more Breeding cultivars with improved water use efficiency (WUE = total biomass production/water use) has been limited by the lack of suitable screening criteria. Theory has predicted an association between WUE and Δ (leaf discrimination against 13C) that could be used in indirect selection for WUE in C3 plants. Several studies have provided empirical evidence supporting this theory but with some exceptions. Earlier studies showed genotypic and drought‐induced variation in Δ in cowpea (Vigna unguiculata (L.) Walp.) and expected associations with leaf gas exchange for drought‐induced effects but not for genotypic effects. Studies were conducted to evaluate directly the association between seasonal WUE and Δ in cowpea. Five contrasting genotypes and two isogenic lines were grown in the field either in pots or under natural soil conditions and subjected to well‐watered or drought treatments. Genotypic rankings for Δ in leaves were consistent in the wet and dry pot and natural soil condition...
Annals of Applied Biology, Apr 1, 1993
Crop growth, water-use efficiency and carbon isotope discrimination in groundnut (Amchis hypogaea... more Crop growth, water-use efficiency and carbon isotope discrimination in groundnut (Amchis hypogaea L.) genotypes under endsf season drought conditions*
Carbon Isotope Fractionation and Plant Water-Use Efficiency
Springer eBooks, 1989
ABSTRACT
Carbon Isotope Discrimination Varies Genetically in C4 Species
Plant Physiology, Feb 1, 1990
Australian journal of agricultural research, 1991
Pod yield response of two spanish (McCubbin and Red Spanish) and two virginia (Virginia Bunch and... more Pod yield response of two spanish (McCubbin and Red Spanish) and two virginia (Virginia Bunch and Q18801) cultivars were compared under a range of irrigation treatments applied at different growth stages on a Xanthozem soil in a subtropical environment in southeast Queensland. Detailed growth and soil water use measurements were taken on a fully irrigated treatment and a treatment which received no rainfall after 83 days after planting (DAP). Soil water deficits occurring during the flowering to the start of pod growth phase (R/I) significantly reduced pod yields (range, 17-25%) relative to the well-watered control plots (I/I) for all cultivars. Where crops were irrigated until 8 3 DAP, then crop water deficits occurred throughout the pod growth phase (I/R), a significant cultivar by irrigation treatment interaction was observed for pod yield. The greatest reduction in yield occurred when severe stress occurred during the pod filling phase (Sh). Significant cultivar variation in pod yield was apparent. Differences in pod yield within this treatment were analysed in terms of a simple framework where pod yield is a function of transpired water (T) , transpiration efficiency (TE) and harvest index (H). Estimates of TE derived from measurements of carbon isotope discrimination in leaves indicated only small variation in TE, and suggest this trait contributed little to pod yield variation in the cultivars used in this experiment. Variation in pod yield among the four cultivars was largely a result of differences in harvest index characteristics.
Annual review of plant physiology and plant molecular biology, Jun 1, 1989
Correlation between the Carbon Isotope Discrimination in Leaf Starch and Sugars of C3 Plants and the Ratio of Intercellular and Atmospheric Partial Pressures of Carbon Dioxide
Plant Physiology, Dec 1, 1988
Photosynthesis and gas exchange
Cambridge University Press eBooks, Oct 27, 1989
Nature, Sep 1, 1993
LETTERS TO NATURE second step reaction of group I introns). We propose that the spliceosome gener... more LETTERS TO NATURE second step reaction of group I introns). We propose that the spliceosome generates a group I-like catalytic site to execute the second step of pre-mRNA splicing. D
Photosynthetic manipulation provides new opportunities for enhancing crop yield. However, underst... more Photosynthetic manipulation provides new opportunities for enhancing crop yield. However, understanding and quantifying effectively how the seasonal growth and yield dynamics of target crops might be affected over a wide range of environments is limited. Using a state-of-the-art cross-scale model we predicted crop-level impacts of a broad list of promising photosynthesis manipulation strategies for C3 wheat and C4 sorghum. The manipulation targets have varying effects on the enzyme-limited (Ac) and electron transport-limited (Aj) rates of photosynthesis. In the top decile of seasonal outcomes, yield gains with the list of manipulations were predicted to be modest, ranging between 0 and 8%, depending on the crop type and manipulation. To achieve the higher yield gains, large increases in both Ac and Aj are needed. This could likely be achieved by stacking Rubisco function and electron transport chain enhancements or installing a full CO2 concentrating system. However, photosynthetic ...
Nature Plants, 2020
Stable isotopes are commonly used to study the diffusion of CO inside photosynthetic tissues of p... more Stable isotopes are commonly used to study the diffusion of CO inside photosynthetic tissues of plants. The standard method to interpret the observed preference for the lighter carbon isotope in C 3 photosynthesis involves the model by Farquhar, O'Leary and Berry, which relates carbon isotope discrimination to physical and biochemical processes inside the leaf. However, under many conditions the model returns unreasonable results for mesophyll conductance to CO 2 diffusion (g m), especially when rates of photosynthesis are low. Here we re-derive the carbon isotope discrimination model using modified assumptions related to the isotope effect of mitochondrial respiration. In particular, we treat the carbon pool associated with respiration as separate from the pool of the primary assimilates. We experimentally test the model by comparing g m values measured with different CO 2 source gases varying in their isotopic composition and show that our new model returns matching g m values that are much more reasonable than those obtained with the old model. We use our results to discuss CO 2 diffusion properties inside the mesophyll.
Functional Plant Biology, 2019
Rice quantitative trait locus (QTL) qDTY12.1 is a major-effect drought yield QTL that was identif... more Rice quantitative trait locus (QTL) qDTY12.1 is a major-effect drought yield QTL that was identified from a cross of Vandana (recipient parent) and Way Rarem (donor parent) through breeding efforts to improve rice yield under upland drought stress conditions. The two main physiological effects previously observed to be related to the presence of qDTY12.1 were (i) increased lateral root growth, and (ii) increased transpiration efficiency. Since relatively more progress has thus far been made on characterising the lateral root growth response related to qDTY12.1, the present study focussed on characterising how qDTY12.1 confers higher transpiration efficiency under upland drought stress in the Vandana background. In a series of field experiments in which stomatal conductance was measured across different times of day in four qDTY12.1 near isogenic lines (NILs), the NILs and Way Rarem showed consistently higher stomatal conductance than Vandana under conditions of low vapour pressure d...
Functional Plant Biology, 2018
Photosynthetic manipulation is seen as a promising avenue for advancing field crop productivity. ... more Photosynthetic manipulation is seen as a promising avenue for advancing field crop productivity. However, progress is constrained by the lack of connection between leaf-level photosynthetic manipulation and crop performance. Here we report on the development of a model of diurnal canopy photosynthesis for well watered conditions by using biochemical models of C3 and C4 photosynthesis upscaled to the canopy level using the simple and robust sun–shade leaves representation of the canopy. The canopy model was integrated over the time course of the day for diurnal canopy photosynthesis simulation. Rationality analysis of the model showed that it simulated the expected responses in diurnal canopy photosynthesis and daily biomass accumulation to key environmental factors (i.e. radiation, temperature and CO2), canopy attributes (e.g. leaf area index and leaf angle) and canopy nitrogen status (i.e. specific leaf nitrogen and its profile through the canopy). This Diurnal Canopy Photosynthesi...
Plant Physiology, 1997
Cuticular properties affect the gas exchange of leaves, but little is known about how much CO2 an... more Cuticular properties affect the gas exchange of leaves, but little is known about how much CO2 and water vapor cross the cuticular barrier or whether low water potentials affect the process. Therefore, we measured the cuticular conductances for CO2 and water vapor in grape (Vitis vinifera L.) leaves having various water potentials. The lower leaf surface was sealed to force all gas exchange through the upper surface, which was stoma-free. In this condition both gases passed through the cuticle, and the CO2 conductance could be directly determined from the internal mole fraction of CO2 near the compensation point, the external mole fraction of CO2, and the CO2 flux. The cuticle allowed small amounts of CO2 and water vapor to pass through, indicating that gas exchange occurs in grape leaves no matter how tightly the stomata are closed. However, the CO2 conductance was only 5.7% of that for water vapor. This discrimination against CO2 markedly affected calculations of the mole fraction...
New Phytologist, 2015
Summary Leaf dark respiration (Rdark) is an important yet poorly quantified component of the glob... more Summary Leaf dark respiration (Rdark) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of Rdark and associated leaf traits. Data for 899 species were compiled from 100 sites (from the Arctic to the tropics). Several woody and nonwoody plant functional types (PFTs) were represented. Mixed‐effects models were used to disentangle sources of variation in Rdark. Area‐based Rdark at the prevailing average daily growth temperature (T) of each site increased only twofold from the Arctic to the tropics, despite a 20°C increase in growing T (8–28°C). By contrast, Rdark at a standard T (25°C, Rdark25) was threefold higher in the Arctic than in the tropics, and twofold higher at arid than at mesic sites. Species and PFTs at cold sites exhibited higher Rdark25 at a given photosynthetic capacity (Vcmax25) or leaf nitrogen concentration ([N]) than species at warmer sites. Rdark25 values at any given Vcmax25 or [N] were higher...
Genetic Variation in the Relationship between Photosynthetic CO2 Assimilation Rate and Stomatal Conductance to Water Loss
Progress in Photosynthesis Research, 1987
Jones (1) has discussed two main reasons for attempting to manipulate stornata by breeding. The f... more Jones (1) has discussed two main reasons for attempting to manipulate stornata by breeding. The first was to maximise productivity and hence yield, by increasing rates of assimilation of CO2. An increase in stomatal conductance would be expected to achieve this in C3 species by increasing the partial pressure of CO2 within the leaf, p., which would be useful in conditions where water supply is not limiting. The second was to improve drought tolerance. A decreased stomatal conductance can aid in this direction, but at some expense to yield potential (yield in well-watered conditions).