Stomatal Conductance, part 1Stomatal Conductance, part 1•ConceptsConcepts– Stomatal anatomy and mechanics•Environmental BiologyEnvironmental Biology– Response of stomata to environmental and physiological forcingspy g g• light•CO2ht th i•photosynthesis• leaf nitrogen•plant functional relationsESPM 129 Biometeorologyplant functional relationsStomataI stand upon a hill so greenAnd spy upon a leafIts occupied with chlorphyll beyond the mind’s beliefIts occupied with chlorphyll, beyond the mind’s beliefMicrocasms everywhereStomatal holes of hellExpiring vaporFor the carbon they inhaleESPM 129 BiometeorologyFor the carbon they inhaleStomatal Features and TerminologyStomatal Features and Terminology•Amphistomatousp– Stomata on both sides of leaves• Hypostomatous– Stomata on the under side of leaves• Fractional area of Leaf05t 5%–0.5 to 5%•C3plants–Elliptically shaped stomata–Elliptically shaped stomata•C4plants–Dumbbell shaped stomataESPM 129 BiometeorologypLeaf Anatomy and StomataUpper epidermisPalisade mesophyllySpongymesophyllLowerIntercellularspaceepidermisStomata &guard cellsESPM 129 BiometeorologyBuckley 2005 New PhytologistESPM 129 BiometeorologyBuckley, 2005, New PhytologistBuckley 2005ESPM 129 BiometeorologyBuckley, 2005Hydro-Active-Negative Feedback HypothesisPe: turgor Pressure EpidermisPt P G dCllPg: turgor Pressure Guard Cell: osmotic pressurewater potentialESPM 129 BiometeorologyBuckley, 2005, New PhytologistIEh IGdCllIon Exchange In Guard Cell,Changes Turgur and StomatalAperture Opensstomata,Stomata,ClosedOpenWaterWaterH+K+, CL-ESPM 129 BiometeorologyStomata, Feedback and Feed Forward LoopsSto ata, eedbac a d eed o a d oops•A decrease of CO2in the intercellular air space, via Ps, 2pand guard cells enables K+ to move into the guard cell and open the stomates. –This allows CO2to diffuse into the leaf for photosynthesis. 2py– In converse, stomata close when exposed to elevated CO2levels• If too much transpiration occurs (eg due to low p(ghumidity or a high radiation load) a direct feed-forward effect occurs by altering the turgor of the guard cells, causing stomatal to close.causing stomatal to close.• When soils dry, roots produce ABA is noted in the transpiration stream. This forces a closing of stomata to conserve waterESPM 129 Biometeorology–This forces a closing of stomata, to conserve water.Feedbacks with Environmental BiologyEnvironmentRg, T, u, vpdstomatal conductancegsAEpositive, +gsleafnegative, -positive, +ppositive,Cileafsoilnegative, -positive, +, +ESPM 129 Biometeorologynductance20253035Stomatal Con51015FeedforwardFeedback0.60.7012340Constant ConductancesgefellEg e esl l()Transpiration0.30.40.5Constant ConductancesNegative FeedbackFeedforwardgfllEeefell()2leaf-air vapor pressure deficit012340.00.10.2Eeefell()ESPM 129 BiometeorologyProposed mechanisms, after Buckley, 2005Proposed mechanisms, after Buckley, 2005• Hydro-Passive feedbackCtli thdlillltdttl–Cannot explain most hydraulically related stomatal responses• eg short-term wrong way response when humidity decreases•Feed Forward MechanismFeed Forward Mechanism– Explains why transpiration declines as humidity gradients between leaf and the air increase– The FeedForward effect is ‘Apparent’•It results from ABA production•It results from ABA production• Can be explained in terms of hysteresis in HydroActive Feedback• Hydro-Active feedbackAtblill ditd f dlltllttt–A metabolically mediated response of guard cells to local water status– Stomata respond similarly to all changes in hydraulic continuum by a mechanism involving active guard cell osmoregulation• humidity, xylem resistance, soil water potential, transpirationESPM 129 BiometeorologyPore ParadoxPore Paradox• if you have a wet surface and dry a quarter of it, yyq,you would expect the evaporation rate to reduce by a fourth. F ll i thi l i ld t th ti–Following this logic one would expect the evaporation rate to decrease by 99% if only 1% of the surface was wet (or had evaporating pores, like stomata). • This linear effect is not observed in nature. – When the holes are arranged in the manner and spacing of a leaf we only observe a 50% reduction inspacing of a leaf we only observe a 50% reduction in evaporation, as compared to a wet surface!! – Why?? ESPM 129 Biometeorologye, airDiffusion out of a Leaf is 3DDnagDnazsvE gsrl1rnrD nDs24e, substomatalcavityBrown and Escombe, 1900ESPM 129 BiometeorologycavityAction Spectra, Role of Light Color on Stomata Functionp, g567Adapted from Sharkey and Raschke 1981gs (mm s-1)23401wavelength350 400 450 500 550 600 650 700 750ESPM 129 BiometeorologyStomatal conductance and sunlight0180.200120.140.160.18gs0060.080.100.120 200 400 600 800 1000 1200 1400 16000.020.040.06PARData of Wilson et alESPM 129 BiometeorologyData of Wilson et al.Stomatal Conductance and Photosynthesis, part 1CO2constant, Light Varying0.180.20CO2constant, Light Varyingm-2 s-1)0.120.140.16oak, varying lightCa: 360 ppmTa: 25 Cgs (mmol m0.060.080.100123456780.000.020.04A (mol m-2 s-1)03568Data of Wilson et alESPM 129 BiometeorologyData of Wilson et al.Stomatal Conductance and Internal CO20.160.120.14gs0.060.080.100 100 200 300 400 500 600 700 8000.020.04CiData of Wilson et alESPM 129 BiometeorologyData of Wilson et al.Stomatal Conductance and Photosynthesis, part 20.160.18ol m-2 s-10.100.120.14gs mmo0.060.080.100 2 4 6 8 101214160.020.04A mol m-2 s-1Why the difference?Light constant and COis varyingESPM 129 BiometeorologyLight constant and CO2is varyingA-Ci Curve15A/Ci curve initiallyAA()ssiAgC Cmol m-2 s-1)912A/Ci curveABAcAlation rate (m69slope is initial value of-gtat second timeADAssimil3slope is value of -gtat second time0 50 100 150 200 250 300 350 4000ESPM 129 BiometeorologyCi (mol mol-1)Stomatal Conductance and Leaf Nitrogenm s-1)14after Schulze et al (1994)ductance (mm1012omatal cond468maximum sto024leaf nitrogen (mg g-`1)5 10152025303540mESPM 129 Biometeorologyvegetation type nitrogen contentspecific leaf areamax stomatal conductancemg/g m2/kg mm/sbroadleaved crops 38.4 23.6 12.2cereals 33.6 25.3 11deciduous conifers 20.7 11.3 3.8evergreen conifers 11 4.1 5.5monsoonal forest 11.4 4.3 3.5sclerophyllous shrubland 11.4 6.9 4.8did ftemperate deciduous forest 19.6 11.5 4.6temperate deciduous fruit trees23.8 10.1temperature broadleaved 13.4 5.7