A novel system for spatial and temporal imaging of intrinsic plant water use efficiency

Instrumentation and methods for rapid screening and selection of plants with improved water use efficiency are essential to address current issues of global food and fuel security. A new imaging system that combines chlorophyll fluorescence and thermal imaging has been developed to generate images of assimilation rate (A), stomatal conductance (gs), and intrinsic water use efficiency (WUEi) from whole plants or leaves under controlled environmental conditions. This is the first demonstration of the production of images of WUEi and the first to determine images of gs from themography at the whole-plant scale. Data are presented illustrating the use of this system for rapidly and non-destructively screening plants for alterations in WUEi by comparing Arabidopsis thaliana mutants (OST1-1) that have altered WUEi driven by open stomata, with wild-type plants. This novel instrument not only provides the potential to monitor multiple plants simultaneously, but enables intra- and interspecies variation to be taken into account both spatially and temporally. The ability to measure A, gs, and WUEi progressively was developed to facilitate and encourage the development of new dynamic protocols. Images illustrating the instrument's dynamic capabilities are demonstrated by analysing plant responses to changing photosynthetic photon flux density (PPFD). Applications of this system will augment the research community's need for novel screening methods to identify rapidly novel lines, cultivars, or species with improved A and WUEi in order to meet the current demands on modern agriculture and food production. © The Author 2013. Published by Oxford University Press on behalf of the Society for Experimental Biology

Rate of leaf production in response to soil water deficits in field pea

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A simple model for minimum crop temperature forecasting during nocturnal cooling

A simple mechanistic model is developed to forecast the minimum temperature reached by the aerial elements of a crop during nocturnal cooling. The model, whose inputs are meteorological data registered at sunset, has two main characteristics: (1) it uses as a framework a two-layer scheme of the surface–atmosphere interaction which allows one to make a clear difference between the temperature of the crop and the temperature of the soil surface; (2) it does not deal with the rather complex resolution of the non-steady-state regime that most of the physical models intend to solve numerically or analytically; it is based upon a static representation of the soil–plant–atmosphere system assumed to be representative of the conditions reached at the end of the night, when minimum temperatures usually occur. The outputs of the model, i.e. minimum crop and soil surface temperatures, are compared to a set of experimental data collected on a pea crop grown near Paris in winter. It appears that the accuracy of the prediction depends mainly on the correct estimation of the nocturnal atmospheric radiation from the weather data observed at sunset. The model performs relatively well under clear sky conditions, but it is less accurate under cloudy conditions. Two simple procedures of estimating long-wave radiation are tested: their accuracy, however, turns out to be relatively poor. When used predictively, the model shows that all other conditions being kept equal, taller crops experience less severe frosts, while crops with greater leaf area index (LAI) experience more severe frosts. The role of soil characteristics (composition, moisture) is also assessed

On the link between potential evaporation and regional evaporation from a CBL perspective

The relationship between potential evaporation and actual evaporation was first examined by Bouchet (Proc Berkeley Calif Symp IAHS Publ, 62:134-142, 1963) who considered potential evaporation as the consequence of regional evaporation due to atmospheric feedbacks. Using a heuristic approach, he derived a complementary relationship which, despite no real theoretical background, has proven to be very useful in interpreting many experimental data under various climatic conditions. Here, the relationship between actual and potential evaporation is reinterpreted in the context of the development of the convective boundary layer (CBL): first, with a closed-box approach, where the CBL has an impermeable lid; and then with an open system, where air is exchanged between the CBL and its external environment. By applying steady forcing to these systems, it is shown that an equilibrium state is reached, where potential evaporation has a specific equilibrium formulation as a function of two parameters: one representing large-scale advection and the other the feedback effect of regional evaporation on potential evaporation, i.e. a kind of "medium-scale advection". It is also shown that the original form of Bouchet's complementary relationship is not verified in the equilibrium state. This analysis leads us to propose a new and more rational approach of the relationship between potential and actual evaporation through the effective surface resistance of the region

A simple model for minimum crop temperature forecasting during nocturnal cooling

A simple mechanistic model is developed to forecast the minimum temperature reached by the aerial elements of a crop during nocturnal cooling. The model, whose inputs are meteorological data registered at sunset, has two main characteristics: (1) it uses as a framework a two-layer scheme of the surface–atmosphere interaction which allows one to make a clear difference between the temperature of the crop and the temperature of the soil surface; (2) it does not deal with the rather complex resolution of the non-steady-state regime that most of the physical models intend to solve numerically or analytically; it is based upon a static representation of the soil–plant–atmosphere system assumed to be representative of the conditions reached at the end of the night, when minimum temperatures usually occur. The outputs of the model, i.e. minimum crop and soil surface temperatures, are compared to a set of experimental data collected on a pea crop grown near Paris in winter. It appears that the accuracy of the prediction depends mainly on the correct estimation of the nocturnal atmospheric radiation from the weather data observed at sunset. The model performs relatively well under clear sky conditions, but it is less accurate under cloudy conditions. Two simple procedures of estimating long-wave radiation are tested: their accuracy, however, turns out to be relatively poor. When used predictively, the model shows that all other conditions being kept equal, taller crops experience less severe frosts, while crops with greater leaf area index (LAI) experience more severe frosts. The role of soil characteristics (composition, moisture) is also assessed

Modelling the daily course of capitulum temperature in a sunflower canopy

A model is proposed to estimate the daily course of capitulum temperature in a sunflower canopy from the beginning of flowering, when the capitulum stands above the canopy. This phase is particularly important for yield determination because it marks the beginning of seed development. The model is based on the equations describing the energy exchanges between the soil-plant system and the atmosphere. The local microclimate surrounding the capitulum is explicitly calculated. The input data are air characteristics at screen level and incident radiations. Some parameters describing canopy architecture and soil water content are also required. The output of the model, i.e., capitulum and leaf temperatures, were successfully compared to measurements made in a field experiment. Simulations have also been made to explore the effects of plant architecture on capitulum temperature. The model can be useful in numerous ecophysiological and genetic studies where thermal environment is taken into account. (c) 2006 Elsevier B.V. All rights reserved

Fortes températures et fonctionnement d'un couvert de pois

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High temperature and water deficit may reduce seed number in field pea purely by decreasing plant growth rate

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