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Berkeley ESPM C129 - Stomatal Conductance

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Stomatal Conductance, part 2Stomatal Conductance, part 2• Environmental Biology, ContinuedRftttitldhilil–Response of stomata to environmental and physiological forcings• humidity deficits•temperaturep– relation to hydraulic conductance– tree age/height. – soil moisture• Diurnal variations of stomata– ample soil moisture– soil moisture deficits• Dynamic ResponsesESPM 129 BiometeorologyStomatal Conductance and Humidity Deficits, DataESPM 129 BiometeorologyStomatal Conductance and Humidity Deficits, DataESPM 129 BiometeorologyCi/Ca and Stomatal ConductanceCi/Ca and Stomatal Conductance081.0Ci/Ca0.60.80.4gs0.0 0.1 0.2 0.3 0.4 0.5ESPM 129 BiometeorologyStomatal Conductance and Soil MoistureESPM 129 BiometeorologyGollan et al 1986, Aust J Plant PhysiolEgekslsoilleaf()700fsoybeanse (s m-1)500600omatal resistance300400sto100200leaf water potential (MPa)-2.00-1.75-1.50-1.25-1.00-0.75-0.50-0.250.000ESPM 129 BiometeorologyBaldocchi, 1982Classic Diurnal Patternsadapted from Korner1.0well-wateredmoderate water deficitssevere soil water deficitsductance060.8ve stomatal cond0.40.6relativ0.2time0 4 8 121620240.0ESPM 129 BiometeorologyESPM 129 BiometeorologyESPM 129 BiometeorologyHydraulic Conductance Modulates Stomatal ConductanceESPM 129 BiometeorologyBrodribb et al New Phytol 2006Dynamic Response of StomataESPM 129 Biometeorologyresponse phases of gs to vpdresponse phases of gs to vpd•low vpd, E is limited by vpd and not gs. As vpd pypgpincreases, E increases so stomatal conductance does not limit transpiration•at mid range values of VPD, stomata close as VPDat mid range values of VPD, stomata close as VPD increases. E remains constant as the increase in the driving force is equal to the change in conductance•At high VPD feedforward effects are noted causing E to•At high VPD, feedforward effects are noted, causing E to decline as V increases more. Hydraulic limitations limit the supply of waterESPM 129 BiometeorologySummary, Key Points• From an environmental standpoint, stomata open and close with changes in light, temperature, humidity, CO2, soil moisture, a hormone (ABA) and transpiration. Stomatal conductance scales with photosynthesis and transpiration. As guard cells respond to light, their solute concentration increases. This allows water to enter the pgguard cell, forcing them to bow and open.• As guard cells respond to CO2, there is a solute efflux from the guard cells. This forces the turgor of the guard cells to decrease and the stomata to close.• Direct effects on stomata occur by high transpiration rates and high humidity deficits. Water loss from the guard cells force them to closeWater loss from the guard cells force them to close.• Soil moisture deficits trigger the product of ABA, which acts as a signal and causes stomata to close.• Stomata tend to open and close to maintain Ci/Ca of C3 plants near 0.7 and Ci/Ca of C4 plants near 0.4.• From a dynamic standpoint, stomatal movement is relatively slow, changing over the course of a half-hour to a change in light. The time response will be faster if a leaf is induced.• The shape of the diurnal pattern of stomatal conductance is a strong indicator as to whether the plant is suffering from soil water deficitswhether the plant is suffering from soil water deficits.• When soil moisture deficits occur, stomatal closure can be patchy.ESPM 129


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Berkeley ESPM C129 - Stomatal Conductance

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