scholarly journals Circadian Regulation Does Not Optimize Stomatal Behaviour

Plants ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 1091
Author(s):  
Víctor Resco de Dios ◽  
William R.L. Anderegg ◽  
Ximeng Li ◽  
David T. Tissue ◽  
Michael Bahn ◽  
...  
Keyword(s):  
Stomatal Conductance ◽  
Circadian Variation ◽  
Vapour Pressure Deficit ◽  
Parameter Estimates ◽  
Circadian Regulation ◽  
Stomatal Behaviour ◽  
Broad Array ◽  
Leaf Level ◽  
Free Running ◽  
Use Efficiency

The circadian clock is a molecular timer of metabolism that affects the diurnal pattern of stomatal conductance (gs), amongst other processes, in a broad array of plant species. The function of circadian gs regulation remains unknown and here, we test whether circadian regulation helps to optimize diurnal variations in stomatal conductance. We subjected bean (Phaseolus vulgaris) and cotton (Gossypium hirsutum) canopies to fixed, continuous environmental conditions of photosynthetically active radiation, temperature, and vapour pressure deficit (free-running conditions) over 48 h. We modelled gs variations in free-running conditions to test for two possible optimizations of stomatal behaviour under circadian regulation: (i) that stomata operate to maintain constant marginal water use efficiency; or (ii) that stomata maximize C net gain minus the costs or risks of hydraulic damage. We observed that both optimization models predicted gs poorly under free-running conditions, indicating that circadian regulation does not directly lead to stomatal optimization. We also demonstrate that failure to account for circadian variation in gs could potentially lead to biased parameter estimates during calibrations of stomatal models. More broadly, our results add to the emerging field of plant circadian ecology, where circadian controls may partially explain leaf-level patterns observed in the field.

scholarly journals Does circadian regulation lead to optimal gas exchange regulation?

2017 ◽  
Author(s):  
Víctor Resco de Dios ◽  
Arthur Gessler ◽  
Juan Pedro Ferrio ◽  
Josu G Alday ◽  
Michael Bahn ◽  
...  
Keyword(s):  
Stomatal Conductance ◽  
Gas Exchange ◽  
Vapour Pressure Deficit ◽  
Evolutionary Model ◽  
Time Of Day ◽  
Carbon Gain ◽  
Circadian Oscillation ◽  
Circadian Regulation ◽  
Stomatal Behaviour ◽  
Leaf Level

SummaryOptimal stomatal theory is an evolutionary model proposing that leaves trade-off Carbon (C) for water to maximise C assimilation (A) and minimise transpiration (E), thereby generating a marginal water cost of carbon gain (λ) that remains constant over short temporal scales. The circadian clock is a molecular timer of metabolism that controls A and stomatal conductance (gs), amongst other processes, in a broad array of plant species. Here, we test whether circadian regulation contributes towards achieving optimal stomatal behaviour. We subjected bean (Phaseolus vulgaris) and cotton (Gossypium hirsutum) canopies to fixed, continuous environmental conditions of photosynthetically active radiation, temperature and vapour pressure deficit over 48 hours. We observed a significant and self-sustained circadian oscillation in A and in stomatal conductance (gs) which also led to a circadian oscillation in λ. The lack of constant marginal water cost indicates that circadian regulation does not directly lead to optimal stomatal behaviour. However, the temporal pattern in gas exchange, indicative of either maximizing A or of minimizing E, depending upon time of day, indicates that circadian regulation could contribute towards optimizing stomatal responses. More broadly, our results add to the emerging field of plant circadian ecology and show that molecular controls may partially explain leaf-level patterns observed in the field.

Partial rootzone drying increases water-use efficiency of lemon Fino 49 trees independently of root-to-shoot ABA signalling

2012 ◽  
Vol 39 (5) ◽  
pp. 366 ◽  
Author(s):  
J. G. Pérez-Pérez ◽  
I. C. Dodd ◽  
P. Botía
Keyword(s):  
Stomatal Conductance ◽  
Water Use Efficiency ◽  
Water Potential ◽  
Water Use ◽  
Leaf Water Potential ◽  
Vapour Pressure ◽  
Vapour Pressure Deficit ◽  
Leaf Water ◽  
Use Efficiency ◽  
Partial Rootzone Drying

To determine whether irrigation strategy altered the sensitivity of Citrus leaf gas exchange to soil, plant and atmospheric variables, mature (16-year-old) Fino 49 lemon trees (Citrus limon (L.) Burm. fil. grafted on Citrus macrophylla Wester) were exposed to three irrigation treatments: control (irrigated with 100% of crop potential evapotranspiration, ETc), deficit irrigation (DI) and partial rootzone drying (PRD) treatments,which received 75% ETc during the period of highest evaporative demand and 50% ETc otherwise. Furthermore, to assess the physiological significance of root-to-shoot ABA signalling, the seasonal dynamics of leaf xylem ABA concentration ([X-ABA]leaf) were evaluated over two soil wetting–drying cycles during a 2-week period in summer. Although stomatal conductance (gs) declined with increased leaf-to-air vapour pressure deficit (LAVPD), lower leaf water potential and soil water availability, [X-ABA]leaf was only related to stomatal closure in well irrigated trees under moderate (<2.5 kPa) atmospheric vapour pressure deficit (VPD). Differences in [X-ABA]leaf were not detected between treatments either before or immediately after (<12 h) rewatering the dry side of PRD trees. Leaf water potential was higher in control trees, but decreased similarly in all irrigation treatments as daily LAVPD increased. In contrast, DI and PRD trees showed lower stomatal sensitivity to LAVPD than control trees. Although DI and PRD decreased stomatal conductance and photosynthesis, these treatments did not significantly decrease yield, but PRD increased crop water use efficiency (WUE) by 83% compared with control trees. Thus PRD-induced enhancement of crop WUE in a semiarid environment seems to involve physiological mechanisms other than increased [X-ABA]leaf.

scholarly journals The contribution of PIP2-type aquaporins to photosynthesis in response to increased vapour pressure deficit

2019 ◽  
Author(s):  
D. Israel ◽  
S. Khan ◽  
C.R. Warren ◽  
J.J. Zwiazek ◽  
T.M. Robson
Keyword(s):  
Vapour Pressure Deficit ◽  
High Water ◽  
Regulatory Function ◽  
Wild Type ◽  
Evaporative Demand ◽  
Flow Measurements ◽  
Knockout Mutants ◽  
Leaf Level ◽  
Low Humidity ◽  
Use Efficiency

AbstractRoles of three different plasma membrane aquaporins (PIPs) in leaf-level gas exchange of Arabidopsis thaliana were examined using single, double and triple knockout mutants and compared to the Columbia-0 wild type (WT) plants. Since multiple Arabidopsis PIPs are implicated in conducting carbon dioxide across membranes, we focused on identifying whether the examined isoforms affect photosynthesis, either mediated through the control of stomatal conductance to water vapour (gs) or mesophyll conductance of CO2 (gm) or a combination of both. In two separate studies, we grew Arabidopsis plants in a low humidity environment and under high humidity conditions. We found that the contribution of functional PIPs to gs was larger under conditions of low air humidity when the evaporative demand was high, whereas any effect of lacking PIP function was minimal under higher humidity conditions. The pip2;4 knockout mutants had 44% higher gs than the WT under low humidity conditions, which in turn resulted in an increased photosynthetic rate (Anet). AtPIP2;4 is thus likely to be involved in maintaining a positive water balance and high water use efficiency through mediation of transmembrane water flow. The lack of functional AtPIP2;5 on the other hand did not affect gs, but reduced gm indicating a possible role in regulating CO2 membrane permeability. This potential regulatory function was indeed confirmed by subsequent stopped flow measurements of yeast expressing AtPIP2;5.

Photosynthetic gas exchange and water use in tropical and subtropical populations of the mangrove Aegiceras corniculatum

1998 ◽  
Vol 49 (4) ◽  
pp. 329 ◽  
Author(s):  
Tarek Youssef ◽  
Peter Saenger
Keyword(s):  
Gas Exchange ◽  
Water Use ◽  
Vapour Pressure Deficit ◽  
Photosynthetic Gas Exchange ◽  
Aegiceras Corniculatum ◽  
Stomatal Behaviour ◽  
Arid Conditions ◽  
Air Temperatures ◽  
Quantum Flux ◽  
Use Efficiency

Photosynthetic gas exchange and stomatal behaviour in the tropical (Darwin: 12°25′S) and subtropical (Ballina: 28°50′S) populations of the mangrove Aegiceras corniculatum (L.) Blanco were compared at elevated air temperatures (>32°C) and leaf-to-air vapour pressure deficit (vpd >25 mbar) with a quantum flux at, or above, their light saturation capacity (>600 µmol m-2 s-1). At the lower end of the tested aridity range, the tropical population showed a less conservative water use than the subtropical population. As aridity increased, both populations showed a reduction in stomatal conductance. However, transpiration rates remained higher in the subtropical population at all times, reducing its water-use efficiency from that under less arid conditions. At extreme aridity (temperature >37°C and vpd >35 mbar), the efficiency of the evaporative cooling of fully exposed leaves was evident in the leaf-to-air temperature differential which remained minimal in the tropical population while it increased significantly in the subtropical population. Aridity tolerance was more pronounced in individuals from the tropical site than from the subtropical site, as evidenced by a tighter stomatal control on water use in the tropical population. These data suggest that the tropical and subtropical populations of A. corniculatum have different physiological responses to aridity.

scholarly journals Circadian rhythms have significant effects on leaf-to-canopy gas exchange under field conditions

2016 ◽  
Author(s):  
Víctor Resco de Dios ◽  
Arthur Gessler ◽  
Juan Pedro Ferrio ◽  
Josu G Alday ◽  
Michael Bahn ◽  
...  
Keyword(s):  
Stomatal Conductance ◽  
Gas Exchange ◽  
Environmental Conditions ◽  
Circadian Regulation ◽  
Molecular Clocks ◽  
Flux Dynamics ◽  
Vapor Flux ◽  
Leaf Level ◽  
Improved Performance ◽  
Temperature Radiation

AbstractMolecular clocks drive oscillations in leaf photosynthesis, stomatal conductance and other cell and leaf level processes over ~24 h under controlled laboratory conditions. The influence of such circadian regulation over whole canopy fluxes remains uncertain and diurnal CO2and H2O vapor flux dynamics in the field are currently interpreted as resulting almost exclusively from direct physiological responses to variations in light, temperature and other environmental factors. We tested whether circadian regulation would affect plant and canopy gas exchange at the CNRS Ecotron. Canopy and leaf level fluxes were constantly monitored under field-like environmental conditions, and also under constant environmental conditions (no variation in temperature, radiation or other environmental cues). Here we show first direct experimental evidence at canopy scales of circadian gas exchange regulation: 20-79% of the daily variation range in CO2and H2O fluxes occurred under circadian entrainment in canopies of an annual herb (bean) and of a perennial shrub (cotton). We also observed that considering circadian regulation improved performance in commonly used stomatal conductance models. Overall, our results show that overlooked circadian controls affect diurnal patterns of CO2and H2O fluxes in entire canopies and in field-like conditions, although this process is currently unaccounted for in models.

Effect of Mycorrhizal Fungi on Gas Exchange of Micropropagated Guava Plantlets (Psidium guajava L.) during Acclimatization and Plant Establishment

HortScience ◽  
1998 ◽  
Vol 33 (3) ◽  
pp. 501c-501
Author(s):  
Andrés A. Estrada-Luna ◽  
Jonathan N. Egilla ◽  
Fred T. Davies
Keyword(s):  
Tissue Culture ◽  
Stomatal Conductance ◽  
Gas Exchange ◽  
Vapor Pressure ◽  
Mycorrhizal Fungi ◽  
Vapor Pressure Deficit ◽  
Psidium Guajava ◽  
Glomus Etunicatum ◽  
Plant Establishment ◽  
Use Efficiency

The effect of mycorrhizal fungi on gas exchange of micropropagated guava plantlets (Psidium guajava L.) during acclimatization and plant establishment was determined. Guava plantlets (Psidium guajava L. cv. `Media China') were asexually propagated through tissue culture and acclimatized in a glasshouse for eighteen weeks. Half of the plantlets were inoculated with ZAC-19, which is a mixed isolate containing Glomus etunicatum and an unknown Glomus spp. Plantlets were fertilized with modified Long Ashton nutrient solution containing 11 (g P/ml. Gas exchange measurements included photosynthetic rate (A), stomatal conductance (gs), internal CO2 concentration (Ci), transpiration rate (E), water use efficiency (WUE), and vapor pressure deficit (VPD). Measurements were taken at 2, 4, 8 and 18 weeks after inoculation using a LI-6200 portable photosynthesis system (LI-COR Inc. Lincoln, Neb., USA). Two weeks after inoculation, noninoculated plantlets had greater A compared to mycorrhizal plantlets. However, 4 and 8 weeks after inoculation, mycorrhizal plantlets had greater A, gs, Ci and WUE. At the end of the experiment gas exchange was comparable between noninoculated and mycorrhizal plantlets.

scholarly journals The contribution of PIP2-type aquaporins to photosynthetic response to increased vapour pressure deficit

2021 ◽  
Author(s):  
D Israel ◽  
S Khan ◽  
C R Warren ◽  
J J Zwiazek ◽  
T M Robson
Keyword(s):  
Vapour Pressure Deficit ◽  
Air Humidity ◽  
Wild Type ◽  
Knockout Mutant ◽  
Evaporative Demand ◽  
Co2 Transport ◽  
Whole Plant ◽  
Knockout Mutants ◽  
Leaf Level ◽  
Low Humidity

Abstract The roles of different plasma membrane aquaporins (PIPs) in leaf-level gas exchange of Arabidopsis thaliana were examined using knockout mutants. Since multiple Arabidopsis PIPs are implicated in CO2 transport across cell membranes, we focused on identifying the effects of the knockout mutations on photosynthesis, and whether they are mediated through the control of stomatal conductance of water vapour (gs), mesophyll conductance of CO2 (gm) or both. We grew Arabidopsis plants in low and high humidity environments and found that the contribution of PIPs to gs was larger under low air humidity when the evaporative demand was high, whereas any effect of lacking PIP function was minimal under higher humidity. The pip2;4 knockout mutant had 44% higher gs than the wild type plants under low humidity, which in turn resulted in an increased net photosynthetic rate (Anet). We also observed a 23% increase in whole-plant transpiration (E) for this knockout mutant. The lack of functional AtPIP2;5 did not affect gs or E, but resulted in homeostasis of gm despite changes of humidity, indicating a possible role in regulating CO2 membrane permeability. CO2 transport measurements in yeast expressing AtPIP2;5 confirmed that this aquaporin is indeed permeable to CO2.

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