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Plant water regime Regulation of gas exchange by stomatal opening –Stomatal limitation of transpiration rate and photosynthetic rate –Water use efficiency –Global climate change –Antitranspirants
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Regulation of transpiration Limitation of transpiration rate (E) by stomatal conductance (g s ): l sE = ( E/E) / ( g s /g s ) l sE = r s / (r a + r s + r i ) dependent mostly on r a transpiration of canopy is dependent on leaf transpiration and LAI stomatal limitation of transpiration is generally higher than stomatal limitation of photosynthetic rate
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Comparison of transport of water vapour and carbon dioxide in a leaf
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Regulation of photosynthetic rate Stomatal limitation of photosynthetic rate l sPN = ( P N /P N ) / ( g s /g s ) l sF = r s / (r a + r s + r i + r m ) stomatal and nonstomatal limitation of photosynthetic rate determination of photosynthetic rate under high CO 2 concentration, simultaneous measurements of gas exchange and chlorophyll fluorescence, calculation by models Cowan, Farquhar (1977): optimum stomatal regulation = maximum carbon gain at minimum water loss E/ P N = E/ g s / P N / g s = const.
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Grassi and Magnani 2005
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Calculation of stomatal and nonstomatal limitation of photosynthesis
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Homobaric and heterobaric leaves, effect of “stomatal patchiness“
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Photosynthesis under stress Stomatal limitation of photosynthesis Non-stomatal limitation of photosynthesis decrease in g m decrease in carbonic anhydrase activity decrease in ATP formation decrease in carboxylation, decrease in amount and activity of RuBPC, decrease in RuBP regeneration decrease in pigment content due to decrease in their synthesis and increase in their degradation. Car are more stable that Chl. Importance of Car and xanthophylls as defence against photoinhibition decrease in activities of photosystem 1 and 2 often in consequence of damage of chloroplast ultrastructure. PS 2 usually more sensitive than PS 1 (PS 2 - degradation and slow recovery of D1 protein). Indicators are changes in Chl a fluorescence Photoinhibition, leaf movements against photoinhibition Limitation of photosynthesis by accumulation of photosynthates under decreased transport Gene expression, rbcS, rbcL
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Effects of transient and permanent water stress (Monti et al. 2006)
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Effect of water stress on parameters of Chl a fluorescence
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WUE WUE = P N /E 1 mol CO 2 per 300 - 500 (C 3 ), 250 (C 4 ) or 100 (CAM) mol of water (D H2O /D CO2 = 1.7) WUE m = M/E WUE i („intrinsic“ WUE) = P N /g s Under mild stress WUE is usually increased, but under severe stress WUE is often decreased
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Relationship between transpiration rate and photosynthetic rate as affected by irradiance
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Methods for WUE determination Measurements of gas exchange Carbon isotope discrimination 13 C ‰ = (R sample /R standard - 1) 1000, R = 13 C/ 12 C 13 C for CO 2 diffusion in air -7.8 ‰, for CO 2 transport in cytoplasm -9.5 to -17.7 ‰, Rubisco – 23.8 ‰, PEPC – 2.03 ‰ Rubisco PEPC, diffusion 13 C for C 3 plants -23 až -36 ‰, C 4 -9 až -18 ‰, CAM -9 až -36 ‰ 13 C = 13 C air - 13 C leaf Farquhar et al. 1989: 13 C P ‰ = 13 C a - a - (b - a) c i /c a, where 13 Ca - 13 C in air, 13 C P - 13 C in plant, a - 13 C connected with CO 2 diffusion, b - 13 C during carbon fixation by RuBPC, c i /c a - internal and ambient CO 2 concentration ratio higher WUE lower c i /c a lower 13 C
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Carbon discrimination and WUE (Monti et al. 2006)
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Methods for WUE determination Oxygen isotope discrimination (Barbour et al. 2002) 18 O ‰ = (R sample /R standard - 1) 1000, R = 18 O/ 16 O 18 O e = 18 O s + * + k + ( 18 O v - 18 O s - k ) e a /e i where 18 O e - 18 O at site of evaporation, 18 O s - 18 O water source, 18 O v - 18 O in air, * - decrease in water vapour tension due to heavier isotope, k - fractionation during diffusion through air boundary layer and stomata, e a /e i - ratio of ambient and internal water vapour concentration
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Sheshshayee et al. 2005
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Global climate change Elevation of CO 2 concentration Increased temperature More often occurrence of drought
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Different possible effects of predicted climate change
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Effects of increased CO 2 concentration 1) Short-term increase induces increase of P N 2) Long-term increase induces increase or decrease of P N 3) E and g s remain unchanged or decrease 4) WUE increases 5) Water consumption decreases or increases
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Effects of elevated CO 2 concentration
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Erice et al. 2006 Effects of elevated CO 2 concentration
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Antitranspirants 1) film-forming antitranspirants (e.g. polyvinyliden chloride, polyvinyl chloride, polystyrene, polyethylene, polypropylene, silicon) – no compound is more permeable for CO 2 than for water 2) inhibitors of stomata opening (e.g. CO 2, ABA, phenylmercuric acetate) – often expensive or poisonous 3) compound increasing reflectance (e.g. kaolin) in all cases not only decrease in transpiration rate but also in photosynthetic rate and growth, therefore practical use only in special cases
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Time and space scale of processes connected with stomata
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