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Review
, 174 (2), 614-623

Diurnal Variation in Gas Exchange: The Balance Between Carbon Fixation and Water Loss

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Review

Diurnal Variation in Gas Exchange: The Balance Between Carbon Fixation and Water Loss

Jack S A Matthews et al. Plant Physiol.

Abstract

Stomatal control of transpiration is critical for maintaining important processes, such as plant water status, leaf temperature, as well as permitting sufficient CO2 diffusion into the leaf to maintain photosynthetic rates (A). Stomatal conductance often closely correlates with A and is thought to control the balance between water loss and carbon gain. It has been suggested that a mesophyll-driven signal coordinates A and stomatal conductance responses to maintain this relationship; however, the signal has yet to be fully elucidated. Despite this correlation under stable environmental conditions, the responses of both parameters vary spatially and temporally and are dependent on species, environment, and plant water status. Most current models neglect these aspects of gas exchange, although it is clear that they play a vital role in the balance of carbon fixation and water loss. Future efforts should consider the dynamic nature of whole-plant gas exchange and how it represents much more than the sum of its individual leaf-level components, and they should take into consideration the long-term effect on gas exchange over time.

Figures

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Figure 1.
Figure 1.
Interspecific diversity of (A) gs, (B) A, and (C) intrinsic water use efficiency (Wi) of Phaseolus vulgaris, Vicia faba, Triticum aestivum, and Nicotiana tabacum in response to a diurnal (8-h) sinusoidal variation of light intensity (from 0 to 2,000 µmol m−2 s−1). Gas-exchange parameters (gs, A, and Wi) were recorded at 10-s intervals, leaf temperature was maintained at 25°C, and leaf VPD was maintained at 1.3 kPa. A representative plant of each species was grown in the greenhouse at the University of Essex and maintained under well-watered conditions. Under the same pattern of light, the diversity of the temporal response of gs and A between species resulted in large differences in the pattern and magnitude of Wi over the course of the diurnal period, highlighting the importance of processes that may determine the slow decrease of A and gs through the day. PPFD, Photosynthetic photon flux density.
Figure 2.
Figure 2.
Effects of stomatal patchiness on the spatial heterogeneity of gs, A, and Wi in an N. tabacum leaf subjected to a diurnal (8-h) sinusoidal variation in light intensity (from 0 to 2,000 µmol m−2 s−1). (A) Three areas (a, b, and c) of the leaf were measured simultaneously for (B) gs, (C) A, and (D) Wi. Gas-exchange parameters were recorded at 10-s intervals, leaf temperature was maintained at 25°C, and leaf VPD was maintained at 1.3 kPa. All plants were grown in the greenhouse at the University of Essex and were maintained under well-watered conditions. Each leaf cuvette only covered 2 cm2 of the leaf surface (∼300 cm2), providing an insight into the heterogenous response of gas exchange over the leaf surface. Remarkably, despite the differences in A and gs, Wi exhibited a similar trajectory at all sites, questioning how the balance between A and gs is maintained over the leaf surface (see text). PPFD, Photosynthetic photon flux density.
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Figure 3.
Figure 3.
Effects of progressive drought on the response of gs (A), A (B), and Wi (C) in V. faba to a diurnal sinusoidal variation in light intensity (from 0 to 2,000 µmol m−2 s−1; black lines). Gas-exchange parameters (gs, A, and Wi) were recorded at 10-s intervals, leaf temperature was maintained at 25°C, and leaf VPD was maintained at 1.3 kPa. The plant was grown in the greenhouse at the University of Essex. A well-watered plant was subjected to progressive soil drying in the absence of rewatering and measured for 4 d consecutively. Soil water content was quantified via a gravimetric method and is represented with different colors as a percentage of soil water content. The decrease in gs only limited A when soil water content was lower than 30%, revealing the unnecessary water loss occurring with no further gain in A under well-watered conditions. PPFD, Photosynthetic photon flux density.

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