Stomatal conductance of individual leaves was measured in a maize field, together with leaf water potential, leaf turgor, xylem ABA concentration and leaf ABA concentration in the same leaves. Stomatal conductance showed a tight relationship with xylem ABA, but not with the current leaf water status or with the concentration of ABA in the bulk leaf. The relationship between stomatal conductance and xylem [ABA] was common for variations in xylem [ABA] linked to the decline with time of the soil water reserve, to simultaneous differences between plants grown on compacted, non‐compacted and irrigated soil, and to plant‐to‐plant variability. Therefore, this relationship is unlikely to be fortuitous or due to synchronous variations. These results suggest that increased concentration of ABA in the xylem sap in response to stress can control the gas exchange of plants under field conditions.

C4-type photosynthesis is known to vary with growth and measurement temperatures. In an attempt to quantify its variability with measurement temperature, the photosynthetic parameters -the maximum catalytic rate of the enzyme ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) (Vcmax), the maximum catalytic rate of the enzyme phosphoenolpyruvate carboxylase (PEPC) (Vpmax) and the maximum electron transport rate ( These parameters should be further tested with C4 plants for validation. Other model key parameters such as the mesophyll cell conductance to CO2 (gi), the bundle sheath cells conductance to CO2 (gbs) and Michaelis-Menten constants for CO2 and O2 (Kc, Kp and Ko) also vary with temperature and should be better parameterized.

Abstract. Stomatal conductance, leaf water potential, soil water potential and concentration of abscisic acid (ABA) in the xylem sap were measured on maize plants growing in the field, in two treatments with contrasting soil structures. Soil compaction affected the stomatal conductance, but this effect was no longer observed if the soil water potential was increased by irrigation. Differences in leaf water potential did not account for the differences in conductance between treatments. Conversely, the relationship between stomatal conductance and concentration of ABA in the xylem sap was consistent during the experiment. The proposed interpretation is that stomatal conductance was controlled by the root water potential via an ABA message. Control of the stomatal conductance by the leaf water potential or by an effect of mechanical stress on the roots is unlikely.

. 2012 Updated stomatal flux and flux-effect models for wheat for quantifying effects of ozone on grain yield, grain mass and protein yield. Environmental Pollution, 165. 147-157. 10.1016Pollution, 165. 147-157. 10. /j.envpol.2012 Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. Field measurements and open-top chamber experiments using nine current European winter wheat 2 cultivars provided a data set that was used to revise and improve the parameterisation of a stomatal 3 conductance model for wheat, including a revised value for maximum stomatal conductance and 4 new functions for phenology and soil moisture. For the calculation of stomatal conductance for 5 ozone a diffusivity ratio between O 3 and H 2 O in air of 0.663 was applied, based on a critical review 6 of the literature. By applying the improved parameterisation for stomatal conductance, new flux-7 effect relationships for grain yield, grain mass and protein yield were developed for use in ozone 8 risk assessments including effects on food security. An example of application of the flux model at 9the local scale in Germany shows that negative effects of ozone on wheat grain yield were likely 10 each year and on protein yield in most years since the mid 1980s. 11 12 Keywords: Ozone, diffusivity ratio, stomatal flux, flux-effect models, wheat, food security 13 14Capsule 15Improved parameterizations of ozone stomatal conductance model for wheat and new ozone flux-16 effect relationships for risk assessments.

The Alpilles-ReSeDA program was initiated to develop and test methods for interpreting remote sensing data that could lead to a better evaluation of soil and vegetation processes. This article presents the experiment that was setup in order to acquire the necessary data to achieve this goal. Intensive measurements were performed for almost one year over a small agricultural region in the South of France (20 kilometers square). To capture the main processes controlling land-atmosphere exchanges, the local climate was fully characterized, and surface energy fluxes, vegetation biomass, vegetation structure, soil moisture profiles, surface soil moisture, surface temperature and soil temperature were monitored. Additional plant physiological measurements and a full characterization of physical soil parameters were also carried out. After presenting the different types of measurements, examples are given in order to illustrate the variability of soils and plant processes in the area in response to the experienced climate. surface energy fluxes / evapotranspiration / soil moisture / soil physical properties / experiment / vegetation characterization Résumé-Suivi des échanges d'énergie et de masse au cours de l'expérimentation Alpilles-ReSeDA. Le programme Alpilles-ReSeDA a été mis en place pour développer et tester des méthodes permettant une meilleure utilisation des données de télédétection pour le suivi du fonctionnement des sols et des cultures. Cet article présente l'expérimentation qui a été réalisée pour acquérir un jeu de données permettant cette analyse. Des mesures intensives ont été réalisées pendant presque une année sur une petite région agricole du Sud de la France (20 kilomètres carrés). De façon à suivre l'ensemble des processus contrôlant les échanges surface-atmosphère, l'ensemble des paramètres climatiques locaux ont été mesurés, ainsi que les flux d'énergie de surface, les caractéristiques de structure de la végétation et du sol, l'humidité et les températures du sol, la température de surface. Des mesures des paramètres physiologiques des plantes et des caractéristiques physiques des sols ont également été entreprises. Après avoir présenté les différents types de mesures réalisées, des exemples présentant la variabilité des couverts végétaux et des sols dans la zone d'étude sont présentés.