The spatial variations in the stable carbon isotope composition (d 13 C) of air and leaves (total... more The spatial variations in the stable carbon isotope composition (d 13 C) of air and leaves (total matter and soluble sugars) were quantified within the crown of a well-watered, 20-year-old walnut tree growing in a low-density orchard. The observed leaf carbon isotope discrimination (D) was compared with that computed by a three-dimensional model simulating the intracanopy distribution of irradiance, transpiration and photosynthesis (previously parameterized and tested for the same tree canopy) coupled to a biophysically based model of carbon isotope discrimination. The importance of discrimination associated with CO2 gradients encountered from the substomatal sites to the carboxylation sites was evaluated. We also assessed by simulation the effect of current irradiance on leaf gas exchange and the effect of long-term acclimation of photosynthetic capacity and stomatal and internal conductances to light regime on intracanopy gradients in D. The main conclusions of this study are: (i) leaf D can exhibit important variations (5 and 8‰ in total leaf material and soluble sugars, respectively) along light gradients within the foliage of an isolated tree; (ii) internal conductance must be taken into account to adequately predict leaf D , and (iii) the spatial variations in D and water-use efficiency resulted from the short-term response of leaf gas exchange to variations in local irradiance and, to a much lesser extent, from the long-term acclimation of leaf characteristics to the local light regime.
Concern exists about the suitability of laser spectroscopic instruments for the measurement of th... more Concern exists about the suitability of laser spectroscopic instruments for the measurement of the (18)O/(16)O and (2)H/(1)H values of liquid samples other than pure water. It is possible to derive erroneous isotope values due to optical interference by certain organic compounds, including some commonly present in ecosystem-derived samples such as leaf or soil waters. Here we investigated the reliability of wavelength-scanned cavity ring-down spectroscopy (CRDS) (18)O/(16)O and (2)H/(1)H measurements from a range of ecosystem-derived waters, through comparison with isotope ratio mass spectrometry (IRMS). We tested the residual of the spectral fit S(r) calculated by the CRDS instrument as a means to quantify the difference between the CRDS and IRMS δ-values. There was very good overall agreement between the CRDS and IRMS values for both isotopes, but differences of up to 2.3‰ (δ(18)O values) and 23‰ (δ(2)H values) were observed in leaf water extracts from Citrus limon and Alnus cordata. The S(r) statistic successfully detected contaminated samples. Treatment of Citrus leaf water with activated charcoal reduced, but did not eliminate, δ(2)H(CRDS) - δ(2)H(IRMS) linearly for the tested range of 0-20% charcoal. The effect of distillation temperature on the degree of contamination was large, particularly for δ(2)H values but variable, resulting in positive, negative or no correlation with distillation temperature. S(r) and δ(CRDS) - δ(IRMS) were highly correlated, in particular for δ(2)H values, across the range of samples that we tested, indicating the potential to use this relationship to correct the δ-values of contaminated plant water extracts. We also examined the sensitivity of the CRDS system to changes in the temperature of its operating environment. We found that temperature changes ≥4 °C for δ(18)O values and ≥10 °C for δ(2)H values resulted in errors larger than the CRDS precision for the respective isotopes and advise the use of such instruments only in sufficiently temperature-stabilised environments.
Rainfall recycling by evapotranspiration from continental surfaces is certainly the most unknown ... more Rainfall recycling by evapotranspiration from continental surfaces is certainly the most unknown component of the global water cycle. This is due to the large variability of rainfall as well as the heterogeneity of these continental surfaces, both in time and space. Traditional measuring methods such as sap flow, micro lysimeter, water and energy balance estimation (Bowen ratio, eddy correlation) have been used since the 70s for a monitoring of real evapotranspiration fluxes over crops and others plant covers. A complementary method consists in using isotopic biogeochemistry. When making specific hypothesis, it is possible to identify and quantify the different sources of the atmospheric water vapour (vegetation and soil at different scales). Analysis of the heavy stable isotopic ratios of water in both liquid and vapour phases: 18O and 2H can allow determining the history of the water in the soil since the last rainfall event (infiltration, re-evaporation) or the root extraction de...
Recently available laser instruments can directly measure the isotopic composition of water vapou... more Recently available laser instruments can directly measure the isotopic composition of water vapour (delta18O, delta2H) in air. Here, we evaluate the calibration of a wavelength-scanned cavity ring-down spectrometer (CRDS) with vapourised liquid standards. We also quantify the dependency of the measured isotope values on the water concentration for a range of isotopic compositions. In both liquid and vapour samples, we
The response of plants to increasing atmospheric CO2 concentrations will have an important influe... more The response of plants to increasing atmospheric CO2 concentrations will have an important influence on biogeochemical cycles in the future. These responses are physiologically driven, but have important feedbacks to water and nutrient cycles as the plants adjust photosynthetic activity within the constraints of these other cycles. Leaf scale manipulations of CO2 concentration provide us with a wealth of information on the short-term, biochemical response of leaf photosynthesis, but these responses do not translate to whole plant responses under sustained growth at higher CO2 concentrations, as has been evidenced by free air enrichment studies. Here we report on a study into whole plant responses to CO2 concentration using a new, 10m3 isotope-biogeochemistry growth chamber housing small (1.5m) potted Pinus nigra trees under controlled conditions. This chamber is capable of controlling the climatic and CO2 conditions and designed for sampling biogeochemical pools for isotopic analysi...
ABSTRACT The contribution of diffusion processes and leaf temperature variations to the spatial d... more ABSTRACT The contribution of diffusion processes and leaf temperature variations to the spatial distribution of leaf water isotopes.
Sustainable use of Genetic Diversity in Forage and Turf Breeding, 2010
ABSTRACT Depending on root depth and the vertical distribution of water, the soil contributes to ... more ABSTRACT Depending on root depth and the vertical distribution of water, the soil contributes to satisfy the transpiration demand of grass crops. Using soil humidity measurements repeated in time at different depth, the depth of water extraction (DWE) of a species can be measured in pure swards. However, that may be irrelevant in mixed swards because (i) roots of all species can be found in all horizons and (ii) the relationship between root density, soil humidity and water extraction is complex. To date, the use of natural abundance of 18O is the only way to precisely compare the DWE of plants sharing the same ground. The work reported here describes the results obtained in a mixture of Dactylis glomerata, Lolium perenne, Festuca arundinacea grown in dense sward and believed to exhibit various abilities to exploit soil resources. Pure stands were also analysed and compared to the mixed crop. The results showed that when the soil profile exhibited a monotonous gradient of natural 18O abundance in water, the ranking of the DWE of three species was possible and explained the differences in plant water status observed in summer. KeywordsPerennial ryegrass-Tall fescue-Cocksfoot-Water use-Isotopic signature- 18O
The response of plants to increasing atmospheric CO2 concentrations is a key element shaping futu... more The response of plants to increasing atmospheric CO2 concentrations is a key element shaping future biogeochemical cycles. While leaf scale manipulations of CO2 concentration provide us with a wealth of information on the biochemical response of leaf photosynthesis, these responses do not necessarily translate to whole plant responses at higher CO2 concentrations. Evidence from free air enrichment studies show different responses of plant gas exchange parameters in their degree of acclimation to long-term increases in atmospheric CO2, relative to those predicted from the instantaneous responses of leaf-level measurements. However, free air enrichment studies are also limited by the fact that they represent a single step change in CO2 and it is therefore of interest to understand how physiological responses derived from leaf-scale increases in CO2 compare to those from exposing the whole plant to increases CO2 across a range of elevated CO2 concentrations. Here we report on a study i...
This article defends the appropriateness of tobacco-free school policies as an effective tool tow... more This article defends the appropriateness of tobacco-free school policies as an effective tool toward ensuring young people develop into healthy and intellectually strong adults, and demonstrates how such a policy can be introduced into a school district. Health education efforts to eliminate tobacco use are widely considered more effective when carried out in concert with school policies and adult role models offering the consistent message that tobacco use is unhealthy and unacceptable. Studies indicate students who attend schools with strict smoking policies are less likely to begin smoking than students who attend schools without such policies. Through research, support, and guidance, the Colorado Tobacco-Free Schools and Communities Project successfully has assisted almost half the 176 school districts in Colorado to adopt such policies.
The spatial variations in the stable carbon isotope composition (d 13 C) of air and leaves (total... more The spatial variations in the stable carbon isotope composition (d 13 C) of air and leaves (total matter and soluble sugars) were quantified within the crown of a well-watered, 20-year-old walnut tree growing in a low-density orchard. The observed leaf carbon isotope discrimination (D) was compared with that computed by a three-dimensional model simulating the intracanopy distribution of irradiance, transpiration and photosynthesis (previously parameterized and tested for the same tree canopy) coupled to a biophysically based model of carbon isotope discrimination. The importance of discrimination associated with CO2 gradients encountered from the substomatal sites to the carboxylation sites was evaluated. We also assessed by simulation the effect of current irradiance on leaf gas exchange and the effect of long-term acclimation of photosynthetic capacity and stomatal and internal conductances to light regime on intracanopy gradients in D. The main conclusions of this study are: (i) leaf D can exhibit important variations (5 and 8‰ in total leaf material and soluble sugars, respectively) along light gradients within the foliage of an isolated tree; (ii) internal conductance must be taken into account to adequately predict leaf D , and (iii) the spatial variations in D and water-use efficiency resulted from the short-term response of leaf gas exchange to variations in local irradiance and, to a much lesser extent, from the long-term acclimation of leaf characteristics to the local light regime.
Concern exists about the suitability of laser spectroscopic instruments for the measurement of th... more Concern exists about the suitability of laser spectroscopic instruments for the measurement of the (18)O/(16)O and (2)H/(1)H values of liquid samples other than pure water. It is possible to derive erroneous isotope values due to optical interference by certain organic compounds, including some commonly present in ecosystem-derived samples such as leaf or soil waters. Here we investigated the reliability of wavelength-scanned cavity ring-down spectroscopy (CRDS) (18)O/(16)O and (2)H/(1)H measurements from a range of ecosystem-derived waters, through comparison with isotope ratio mass spectrometry (IRMS). We tested the residual of the spectral fit S(r) calculated by the CRDS instrument as a means to quantify the difference between the CRDS and IRMS δ-values. There was very good overall agreement between the CRDS and IRMS values for both isotopes, but differences of up to 2.3‰ (δ(18)O values) and 23‰ (δ(2)H values) were observed in leaf water extracts from Citrus limon and Alnus cordata. The S(r) statistic successfully detected contaminated samples. Treatment of Citrus leaf water with activated charcoal reduced, but did not eliminate, δ(2)H(CRDS) - δ(2)H(IRMS) linearly for the tested range of 0-20% charcoal. The effect of distillation temperature on the degree of contamination was large, particularly for δ(2)H values but variable, resulting in positive, negative or no correlation with distillation temperature. S(r) and δ(CRDS) - δ(IRMS) were highly correlated, in particular for δ(2)H values, across the range of samples that we tested, indicating the potential to use this relationship to correct the δ-values of contaminated plant water extracts. We also examined the sensitivity of the CRDS system to changes in the temperature of its operating environment. We found that temperature changes ≥4 °C for δ(18)O values and ≥10 °C for δ(2)H values resulted in errors larger than the CRDS precision for the respective isotopes and advise the use of such instruments only in sufficiently temperature-stabilised environments.
Rainfall recycling by evapotranspiration from continental surfaces is certainly the most unknown ... more Rainfall recycling by evapotranspiration from continental surfaces is certainly the most unknown component of the global water cycle. This is due to the large variability of rainfall as well as the heterogeneity of these continental surfaces, both in time and space. Traditional measuring methods such as sap flow, micro lysimeter, water and energy balance estimation (Bowen ratio, eddy correlation) have been used since the 70s for a monitoring of real evapotranspiration fluxes over crops and others plant covers. A complementary method consists in using isotopic biogeochemistry. When making specific hypothesis, it is possible to identify and quantify the different sources of the atmospheric water vapour (vegetation and soil at different scales). Analysis of the heavy stable isotopic ratios of water in both liquid and vapour phases: 18O and 2H can allow determining the history of the water in the soil since the last rainfall event (infiltration, re-evaporation) or the root extraction de...
Recently available laser instruments can directly measure the isotopic composition of water vapou... more Recently available laser instruments can directly measure the isotopic composition of water vapour (delta18O, delta2H) in air. Here, we evaluate the calibration of a wavelength-scanned cavity ring-down spectrometer (CRDS) with vapourised liquid standards. We also quantify the dependency of the measured isotope values on the water concentration for a range of isotopic compositions. In both liquid and vapour samples, we
The response of plants to increasing atmospheric CO2 concentrations will have an important influe... more The response of plants to increasing atmospheric CO2 concentrations will have an important influence on biogeochemical cycles in the future. These responses are physiologically driven, but have important feedbacks to water and nutrient cycles as the plants adjust photosynthetic activity within the constraints of these other cycles. Leaf scale manipulations of CO2 concentration provide us with a wealth of information on the short-term, biochemical response of leaf photosynthesis, but these responses do not translate to whole plant responses under sustained growth at higher CO2 concentrations, as has been evidenced by free air enrichment studies. Here we report on a study into whole plant responses to CO2 concentration using a new, 10m3 isotope-biogeochemistry growth chamber housing small (1.5m) potted Pinus nigra trees under controlled conditions. This chamber is capable of controlling the climatic and CO2 conditions and designed for sampling biogeochemical pools for isotopic analysi...
ABSTRACT The contribution of diffusion processes and leaf temperature variations to the spatial d... more ABSTRACT The contribution of diffusion processes and leaf temperature variations to the spatial distribution of leaf water isotopes.
Sustainable use of Genetic Diversity in Forage and Turf Breeding, 2010
ABSTRACT Depending on root depth and the vertical distribution of water, the soil contributes to ... more ABSTRACT Depending on root depth and the vertical distribution of water, the soil contributes to satisfy the transpiration demand of grass crops. Using soil humidity measurements repeated in time at different depth, the depth of water extraction (DWE) of a species can be measured in pure swards. However, that may be irrelevant in mixed swards because (i) roots of all species can be found in all horizons and (ii) the relationship between root density, soil humidity and water extraction is complex. To date, the use of natural abundance of 18O is the only way to precisely compare the DWE of plants sharing the same ground. The work reported here describes the results obtained in a mixture of Dactylis glomerata, Lolium perenne, Festuca arundinacea grown in dense sward and believed to exhibit various abilities to exploit soil resources. Pure stands were also analysed and compared to the mixed crop. The results showed that when the soil profile exhibited a monotonous gradient of natural 18O abundance in water, the ranking of the DWE of three species was possible and explained the differences in plant water status observed in summer. KeywordsPerennial ryegrass-Tall fescue-Cocksfoot-Water use-Isotopic signature- 18O
The response of plants to increasing atmospheric CO2 concentrations is a key element shaping futu... more The response of plants to increasing atmospheric CO2 concentrations is a key element shaping future biogeochemical cycles. While leaf scale manipulations of CO2 concentration provide us with a wealth of information on the biochemical response of leaf photosynthesis, these responses do not necessarily translate to whole plant responses at higher CO2 concentrations. Evidence from free air enrichment studies show different responses of plant gas exchange parameters in their degree of acclimation to long-term increases in atmospheric CO2, relative to those predicted from the instantaneous responses of leaf-level measurements. However, free air enrichment studies are also limited by the fact that they represent a single step change in CO2 and it is therefore of interest to understand how physiological responses derived from leaf-scale increases in CO2 compare to those from exposing the whole plant to increases CO2 across a range of elevated CO2 concentrations. Here we report on a study i...
This article defends the appropriateness of tobacco-free school policies as an effective tool tow... more This article defends the appropriateness of tobacco-free school policies as an effective tool toward ensuring young people develop into healthy and intellectually strong adults, and demonstrates how such a policy can be introduced into a school district. Health education efforts to eliminate tobacco use are widely considered more effective when carried out in concert with school policies and adult role models offering the consistent message that tobacco use is unhealthy and unacceptable. Studies indicate students who attend schools with strict smoking policies are less likely to begin smoking than students who attend schools without such policies. Through research, support, and guidance, the Colorado Tobacco-Free Schools and Communities Project successfully has assisted almost half the 176 school districts in Colorado to adopt such policies.
Uploads
Papers by Patricia Richard