Presentation on theme: "Last Time Modeling Photosynthesis Farquhar & von Caemmerer Equations Physiological and Environmental Controls Stomate control Water stress and the A/Ci."— Presentation transcript:
Last Time Modeling Photosynthesis Farquhar & von Caemmerer Equations Physiological and Environmental Controls Stomate control Water stress and the A/Ci Curve
Today Anatomical regulation of photosynthesis Light Acclimation - Sun vs. Shade leaves Temperature responses of photosynthesis and thermal acclimation Photosynthetic pathway variation C3, C4, CAM
Compare to Adaptation Both occur in within the lifetime of an organism Acclimation vs. Acclimatization Acclimate - Short-term physiological and behavioral adjustments Acclimatize (Acclimatization) - Longer term physiological change over a year. Often extensive physiological changes in tolerances. The physiological change of an organism to changes in climate or environment.
Carbon and Water Flux Modeled by Stomatal Conductance Resistance = 1 / conductance 1/conductance = g Photosynthetic flux A ~ J CO2 = (C i -C a ) / ∑ r i = g CO2 (C i - C a ) Water flux (transpiration) E ~ J H2O = (e i -e a )/ ∑ r = g H2O (e i - e a ) where e = vapor partial pressures in the leaf or air (recall, its’ the hydrated surface within the intercellular airspace that is the site of evaporation…thus, temperature dependent)
Anatomical Regulation of C 3 Photosynthesis via modification of pathway resistance Three Primary Factors Cell Size: Changes in cell surface area and resistance of CO 2 diffusion Mesophyll Thickness: Changes in cell surface area Changes in chloroplast volume Molecular distance of transport Percent Air Space: Changes in cell surface area Changes in chloroplast volume Changes in tissue blockage of CO 2 molecules
Cell Size Mesophyll Thickness % air space Cell surface area per unit leaf area Volume of chlorophyllous tissue per unit leaf area Molecular travel distances Tissue blockage of CO2 molecules Transport Resistance Enzyme Resistance Intercellular airspace resistance Photosynthetic rate Maximize photosynthesis - minimize resistances
Let’s Compare The Resistances of Three Leaves How Can Plant Anatomy Influence A and E?
Resistance Diffusion speed Photosynthesis Low resistance but thicker leaf (increased diffusion times, lower photosythesis per unit volume) High chlorophyll per unit volume but high resistance Selection has acted to maximize Chlorophyll per unit volume and minimize resistance Compromise Maximize photosynthesis
Influence of Light Environment on Photosynthesis Light Acclimatization and Adaptations
What is changing in these plants in terms of allocation? physiology?
Group Project What will natural selection operate on? You now know most of the basics of what limits photosynthesis Depending on the environment photosynthesis is limited by potentially many factors… Let’s think about leaves growing in a sunny environment and leaves growing in a shady environment How will they differ in terms of leaf anatomy, biochemistry, and gas exchange?
Anatomy of Sun leaves compared to Shade leaves -Cell Size, -Surface areas, -cuticle thickness, -thickness of palisade parenchyma (extra cell layer) -chloroplast per unit area Biochemistry of Sun leaves compared to Shade leaves -Chlorophyll per chloroplast -Nitrogen and Rubisco per unit area -Number of light harvesting complex per unit area -Chlorophyll per unit leaf area Gas Exchange of Sun leaves compared to Shade leaves -photosynthetic and respiratory capacity per unit area -photosynthetic capacity and respiration per unit dry mass -quantum yield WILLTHESE TRAITS INCREASE, DECREASE, OR REMAIN CONSTANT? List of leaf traits associated with photosynthesis Compare Sun to Shade Leaves
Cross-section of sun (L) and shade leaf (R) (C. album ) Anatomy of Sun leaves compared to Shade leaves -smaller cells, -smaller surface and interveinal areas, -thicker cuticles, -thicker palisade parenchyma (extra cell layer) -More chloroplast per unit area Gas Exchange of Sun leaves compared to Shade leaves -photosynthetic and respiratory capacity per unit area is higher -photosynthetic capacity and respiration per unit dry mass is similar -quantum yield is similar Biochemistry of Sun leaves compared to Shade leaves -Chlorophyll per chloroplast is lower -Nitrogen and Rubisco per unit area is higher -Light harvesting complex per unit area is lower -Chlorophyll per unit leaf area is similar
Mean leaf size of leaves of Northofagus. pumilio, collected at different altitudes at the volcano Lanin. Black points refer to shade leaves and yellow points to sun-exposed leaves. ~franzari/UVB/haupt.htm Specific leaf area (SLA) of leaves of Northofagus. pumilio, collected at different altitudes at the volcano Lanin. Black points refer to shade leaves and yellow points to sun-exposed leaves. Sun leaves higher SLA (cm 2 g -1 ) Mean Leaf Area cm 2 Elevation Sun Shade Sun
Sun vs. Shade leaves Why such changes! Sun Leaves (Maximize Carboxylation limitations) Thicker leaves - taller Palisade Cells and/or more layers Thicker cuticles to minimize water loss (sun is hot!) Shade Leaves (Minimize Light Limitations) More Spongy mesophyll - -air spaces increases the efficiency of light absorbance by influencing light scattering Invest more in light harvesting complex within chloroplast -to maximize what little light is available How? - Adding more cells and chloroplasts per leaf area!
(Light Reactions) Light Limiting Carboxylation Limited (Carbon reactions) What is changing in these plants in terms of allocation?
Influence of Temperature on Photosynthesis Thermal Acclimation and Adaptations
Temperature influences on Photosynthesis Open circles - Photosynthesis at 3kPa O 2 Black circles - Photosynthesis at 18k Pa O 2
Temperature Kinetic processes= e -E/kT Biological Rate Enzymes denature Carbon fixation reactions Oxygenation reaction A Opt Boltzmann Temperature response
Plants show ‘optimal’ temperature for photosynthesis -Optimal peak is close to normal growth temperature -Below optimum photosynthesis is limited by carbon fixation reactions -At high temperatures oxygenating reaction of Rubisco increases more than carboxylation photorespiration increasingly more important Why Photorespiration more important at high temps? - Solubility of CO 2 decreases with increasing temperature More strongly than does O 2 -temperature influences kinetic properties of Rubisco (value of K m )
Shift in A max with growing season temperature Evolutionary response In A max within and between populations
‘Plastic’ response of leaves grown in differing temperatures
Plants show an optimum temperature for A max Adaptation to high temperatures -saturation of membrane lipids (decreases membrane fluidity) At low temperatures (before freezing) chilling injury (electron transport slows down) -Loss of activity of cold-sensitive enzymes -Decrease in membrane fluidity -Change in the activity of membrane associated enzymes And processes
Adaptations to cold temperatures -Increase concentrations of Rubisco -higher leaves of cytosolic Fru 1,6-bisphosphatase increase rates of Sucrose production -Rates of PSII activity can be altered (increased electron transport in colder environments)
Maximum rates of photosynthesis by arctic and alpine plants are similar to temperate and tropical species!
Photosynthetic capacity Range of leaf conductance Arid habitats Mesic habitats Variation between species associated with adaptation to aridity (WUE ! ) Variation within and between species associated with variation in PSN capacity, leaf N content, leaf morphology/ontogeny Why Variability in Leaf Conductance and Photosynthetic Capacity? Selection is acting to maximize dE/dA in differing environments
Problems with C3 photosynthesis Increase in photorespiration - in hot dry conditions Why? - Competition between O 2 and CO 2 for Rubisco binding site [O 2 ] / [CO 2 ] inside the leaf increases Photorespiration increases when
Photosynthetic Pathway Variation Focus until now has been on C3 photosynthesis Variation in biochemistry of photosynthesis exists and has ecological implications – CAM and C4 photosynthesis Biochemistry worked on by Hatch and Slack 1966 C4 and CAM are two evolutionary solutions to the problem of maintaining photosynthesis with stomata partially or completely closed on hot, dry days (Carbon Concentrating Adaptations)
Photosynthetic Pathway Variation C3 – CO 2 fixation by Rubisco; PGA (phosphoglycerate – a 3 carbon sugar) is the product of initial carboxylation C4 – CO 2 fixation by PEP carboxylase to produce OAA (oxaloacetate – a 4 carbon acid); C4 then transported within the leaf, decarboxylation and re-fixation by Rubisco. CAM (crassulacean acid metabolism) – CO 2 fixation by PEP carboxylase to OAA, but results in the production of malic acid in the vacuole during the day and de- carboxylation and fixation at night
C3, C4 and CAM C4 photosynthesis results in CO 2 concentrating at the site of carboxylation, by a spatial specialization of biochemistry – Kranz Anatomy (Bundle Sheath Design) CAM photosynthesis results in CO 2 concentration at the site of carboxylation by a temporal specialization of biochemistry
(1)Carboxylation of PEP (by PEP Carboxylase) produces C4 acids in the mesophyll cells (2) Organic acids are transported to the bundle sheath cells (3) Organic acids are decarboxylated in bundle sheath cells producing CO 2 (4) CO 2 is assimilated by Rubisco and PCR cycle (5) Compounds return to the mesophyll cells to regenerate more PEP Central Steps in C4 photosynthesis
Comparison of leaf anatomy of C3 and C4 plants. Reproduced through the courtesy of Dr. Stephen Grace, University of Arkansas. article.php?ch=e&id=290 Anatomical differences between C3 and C4 plants
article.php?ch=e&id=290 Figure 2 Diagrams of Kranz anatomy in a C4 dicot and a C4 grass. (A) In the C4 dicot Atriplex rosea (NAD-ME), the bundle sheath cells form only a partial sheath around the vascular tissue. Only the radially arranged mesophyll cells that are in contact with the bundle sheath express PEPCase. (B) In the C4 grass Panicum capillare (NAD-ME), the large vascular bundles are surrounded by both a non-photosynthetic bundle sheath (mestome sheath) and the photosynthetic bundle sheath. Anatomy/Leaves/Leaves.html Corn leaf cross-section Anatomy of C4 plants Kranz Anatomy (Bundle Sheath Design)
CO 2 C4C4 Mesophyll CO 2 concentration 100 mol mol -1 C3C3 PEP C4C4 Bundle Sheath CO 2 concentration 2000 mol mol -1 PCR (Calvin Cycle) C3C3 CHO PEP Carboxylase C4 plants have a mechanism to enhance the partial pressure of CO 2 at the site of Rubisco - so that oxygenation reaction of Rubisco is virtually inhibited Rubisco
Three subtypes of C4 photosynthesis (!) Based on the enzyme involved in the decarboxylation of the C4 compounds transported to the vascular bundle sheath
Compensation points for C3 and C4 differ The Compensation Point Net Assimilation = gross photosynthesis - respiration
CAM Bromeliaceae Cactaceae Generally in Succulent Plants
The first recognition of the nocturnal acidification process(CAM) can be traced to the Romans, who noted that certain succulent plants taste more bitter in the morning than in the evening. (Rowley, 1978)
CAM photosynthesis results in CO 2 concentration at the site of carboxylation by a temporal specialization of biochemistry
The above diagram compares C4 and CAM C4 photosynthesis. Both adaptations are characterized by initial fixation of CO 2 into an organic acid such as malate followed by transfer of the CO 2 to the Calvin cycle. In C4 plants, such as sugarcane, these two steps are separated spatially; the two steps take place in two cell types. In CAM C4 plants, such as pineapple, the two steps are separated temporally (time); carbon fixation into malate occurs at night, and the Calvin cycle functions during the day. Both C4 and CAM C4 are two evolutionary solutions to the problem of maintaining photosynthesis with stomata partially or completely closed on hot, dry days. However, it should be noted, that in all plants, the Calvin cycle is used to make sugar from carbon dioxide. C4 CAM Comparing C3 and C4 photosynthesis
CO 2 C 4 (Malic Acid) Dark CO 2 concentration 150 mol mol -1 CHO PEP Acidification of Vacuole CO 2 C4C4 Light CO 2 concentration 4000 mol mol -1 CHO Malic Acid C3C3 PEP Carboxylase Rubisco PCR (Calvin Cycle) CAM C4 PHOTOSYNTHESIS
DARKLight CO 2 Fixation = by BOTH PEP carboxylase and RUBISCO