Physiology Of Environmental Effects On Photosynthesis

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1 Physiology Of Environmental Effects On Photosynthesis
PREview slides: 2, 7, 8, 10, 11, 12, 13, 16, 17, 20, 22 Study the main message of the slide; we will build on these in class.

2 Spectrum of Solar Energy Source
Solar spectrum shows the wavelength distribution of incoming solar energy and the absorption of certain wavelengths of sun light. The dips beyond 700 nm are due to absorption of photons by molecules such as carbon dioxide, water vapor and the like in the atmosphere.

3 Chloroplast Structure
Two photosystems are embeded in the thylkoid membrane

4 Transfer of Energy in Photosystems
Chlorophyll arranged in antenna & reaction center complexes antenna- collects light and transfers its energy reaction center- receives light from antenna complexes; this energy drives photochemical carbon fixation Electron acceptor P680 H2O Electron donor

5 Generation of Reducing Power
Final electron acceptor Electron transport is driven by energy derived from two photosystems Electron transporters Electron donor Electron acceptor 5 CL

6 essential for C fixation *Proton gradient drives ATP production
Key Concepts essential for C fixation H+ * Protons consumed Energy converted H+ *Proton gradient drives ATP production * Protons released Energy stored O F THYLAKOID

7 Necessary inputs, products of photosystem
Calvin Cycle * * 3 Necessary inputs, products of photosystem * * 3 essential steps PRE 7

8 C2 Oxidative Photosynthetic Carbon Cycle
input output Fixes O2 instead of CO2 AND loses a CO2 PCR PCO Recovery of 1 carbon In air oxygen is also fixed causes loss of 1 CO2

9 C-4 Carbon Fixation Cycle Lessens C Loss
concentrateCO2 Regerate recepter fix CO2 exported metabolites

10 C4 CO2 Concentrating Mechanism
Anatomical arrangement in leaves of C4 plants C4 CO2 Concentrating Mechanism C4 PS C3 PS

11 CAM: CO2 Concentrating Mechanism
CAM- Crassulacian Acid Metabolism Stomates open at night and leaves fix CO2 in the dark, producing malic acid, which is stored in vacuoles… During the day the stomates close and the leaves decarboxylate malate, releasing CO2 . Leaves generate reducing potential in the sun, which is used to fix CO2 with the stomates closed. Water loss thorough the open stomates occurs at night.

12 CO2 Concentrating Mechanisms
CAM adaptive advantages cost: concentrating CO2 2 ATP per CO2 CAM PS- high water use efficiency found in many plant families…cactus, pineapple C3 PS under unstressed conditions… CAM PS under water, salt, or heat stress… Adaptive advantage… water use efficiency CO2 fixed per unit of water evaporated: C = 1 CO2 / 600 H2O C = 1 CO2 / 300 H2O CAM = 1 CO2 /100 H2O

13 General Overview environmental impact on photosynthesis:
key factors: light, temperature, CO2 level, drought responses occur at all levels- gene, cell, leaf, plant principle of emergent properties: at each higher level of organization new properties emerge which are not evident from processes that occur at the previous level system organization imparts unforeseen capabilities plant-level acclimation integrates all levels even if one factor seems to be limiting, all factors and various environmental responses of a plant interact to produce an integrated plant response

14 Light, Leaves and Photosynthesis
Distribution of leaf chloroplasts responding to light intensity. DARK LOW HIGH

15 Intact Leaf Responses to Light
low range high range Intact Leaf Responses to Light CL 15 Response of photosynthesis to irradiance

16 Intact Leaf Responses to Light
Adaptation Intact Leaf Responses to Light genetically adapted species Plants are genetically adapted to a particular range of light level… - the antenna complex differs genetically in sun plants and in shade plants Sun adapted plant…curve- PS rate is capable of acclimating quickly to respond to high light levels Shade adapted plant response curve- PS rate becomes light saturated at relatively low light levels. Unable to acclimate to high light levels. 16 PRE CL Adaptive responses of sun & shade plants

17 Intact Leaf Responses to Light
Acclimation Acclimates to light level to which it is exposed Light response curve of adapted species becomes adjusted to light level at which plant was raised shade grown sun plant PS rate becomes light saturates at relatively low light levels… sun grown plant... saturaates at high light levels Intact Leaf Responses to Light Fig 9.10 Acclimation of leaves of Atriplex to irradiance

18 Intact Leaf Responses to Light 1
Intact Leaf Responses to Light 1. leaf abscission limits number of leaf layers 2. leaf area index: ratio leaf area to the projected area of the leaf canopy ~ generally a value of 4 for efficient light use… i.e. 4 layers absorb light 3. photosynthesis of canopy as a whole does not saturate at high light CL 18 Light saturation of photosynthesis in leaf and canopy

19 Responses to Light Intact Leaf Light Stress
With light saturation excess light is absorbed Excess light energy: May be dissipated without harm… by several adaptive mechanisms The rest damages the plant… slight to extensive and prolonged damage Responses to Light Intact Leaf Light Stress CL 19 Excess light energy absorbed by leaves

20 Responses to Temperature
optimal temperature varies with species and with growth conditions Photosynthesis as function of temperature At suboptimum temperatures, plants under high CO2 are able to respond to temperature increases to a greater extent than at ambient CO2 At above optimum temperature damage is more pronounced t high CO2.

21 Responses to Temperature
inefficiency is caused largely by photorespiration the effect of which is essentially eliminated in C4 plants C4 advantage realized in climates with warm to hot summers; generally below 45o latitude. CL 21 Effect of temperature on quantum yield (PS efficiency)

22 Responses to Temperature
Fig 9.14 Heat budget of a leaf in sunlight

23 Photosynthetic Responses to Carbon Dioxide
Responses of photosynthesis to CO2 level CO2 level limits PS rate as irradiance increases CO2 limitation causes excess light to be absorbed CO2 a factor in plant productivity in C3 plants Initial rate may increase at higher CO2;; in most plants it slows back down as nutrient supply limits growth In C4 plant photosynthesis does not increase with CO2 Increased CO2 levels increase air temperature which slows C3 but not C4 photosynthesis.