Modified by Georgia Agricultural Education Curriculum Office Photosynthesis Modified by Georgia Agricultural Education Curriculum Office July, 2002

3 carbon sugars produced What is the transport sugar in plants? Photosynthesis - Basics 3CO2 + 6H2O C3H6O3 + 3O2 + 3H2O 3 carbon sugars produced What is the transport sugar in plants? O2 is liberated from the H2O

Energy and wavelength energy as wavelength Photosynthesis - Light

Color Wavelength Energy Violet short high Blue Green Yellow Red Photosynthesis - Visible Spectrum Color Wavelength Energy Violet short high Blue Green Yellow Red Far-Red long low

Color Wavelength Energy Violet short high Blue Green Yellow Red Photosynthesis - PS Action Spectrum Color Wavelength Energy Violet short high Blue Green Yellow Red Far-Red long low Peak between 430 - 500 nm Peak at about 680 nm

Electrons kicked up to higher energy level Absorbed light has 3 fates: Photosynthesis - Role of Pigments Electrons kicked up to higher energy level Absorbed light has 3 fates: 1. Fluorescence 2. Transfer energy 3. Transfer electrons

yellow pigments are carotenoids Photosynthesis - Pigments Chlorophyll a required pigment, “the hanger” Chlorophyll b accessory pigment, “the tin foil” Carotenoids anti-oxidants, protect the chlorophyll Figure 7-13 in text yellow pigments are carotenoids

Energy Transduction Rxns light dependent Carbon Fixation Photosynthesis - The Reactions Energy Transduction Rxns light dependent harvesting energy from the sun Carbon Fixation either light or dark requires energy from 1st rxns fixes CO2 into sugars Both occur in chloroplast

note similarities to figure 6-16 Photosynthesis - Energy Transduction Rxns Light dependent 2 photosystems, linkage pumps protons “purpose”: to generate ATP & NADPH Figure 7-15 in text note similarities to figure 6-16

Dependent on energy Calvin Cycle C3 pathway Photosynthesis - Carbon Fixation Rxns Dependent on energy “purpose”: to fix carbon, storing energy in bonds Calvin Cycle C3 pathway 1st product contains 3 carbons occurs in most plants

Rubisco affinity Photosynthesis - Photorespiration binds with both O2 and CO2 when it binds with O2, carbon is bound into other products energy must be used to salvage the C rubisco contains nitrogen which is commonly the limiting nutrient

“Warm season” plants Photosynthesis - C4 Pathway many native prairie grasses 1st product contains 4 carbons use BOTH C3 and C4 pathways C fixed by PEP carboxylase in mesophyll prefers CO2 over O2 handles photorespiration problems product is shipped to bundle sheath cells Kranz anatomy the key to the C4 pathway: spatial separation

C4 - Kranz Anatomy C3 C4 and C3 Pathways - Differences in Anatomy CO2 H2O CO2 H2O H2O and CO2 pass through stomatal openings

Succulent plants (like cacti) Photosynthesis - CAM Pathway Succulent plants (like cacti) Crassulacean acid metabolism (CAM) use BOTH C3 and C4 pathways C fixed by PEP carboxylase in DARK allows plants to close stomata product is used in same cells must have HUGE vacuoles to store C the key to the CAM pathway: temporal separation allows internal cycling during drought pineapple is CAM

C4 - Kranz Anatomy C3 C4 and C3 Pathways - Differences in Anatomy CO2 H2O CO2 H2O H2O and CO2 pass through stomatal openings

Photosynthesis - C4 and C3 Pathways 10 20 30 40 50 14.0 For a given growth rate, C3 species use almost twice as much water as C4 species. (i.e., they have lower water use efficiencies (WUE) Transpiration both types 11.2 C4 C3 8.4 Net Photosynthesis (µmol m-2 s-1) Transpiration (mmol m-2 s-1) 5.6 2.8 160 320 480 640 Leaf Conductance (mmol m-2 s-1)

C4 and C3 Pathways - Light Saturation C3 species become light saturated more quickly provides advantage in low light environments C4 C3 Carbon Gain Light

C4 and C3 Pathways - Effect of Temperature 60 330 ppm 1000 ppm 50 C4 40 Net Photosynthesis (µmol m-2 s-1) 30 C3 20 C3 C4 10 20 30 40 50 20 30 40 50 Leaf Temperature (°C)

C4 and C3 Pathways - Photorespiration 60 C3, Low [O2] Conflict between CO2 and O2 places C3 species at a disadvantage C4 species are able to concentrate CO2 providing an advantage under low CO2 conditions C3 Ambient [O2] 50 40 C4, Ambient [O2] Net Photosynthesis (µmol m-2 s-1) 30 20 10 -10 100 200 300 400 500 600 Intercellular [CO2] (ppm)

Global Change - CO2, N and Diversity Global N Fixation CO2 Concentration “Natural” Anthropogenic 1920 1980 2000 Year Year Diversity Time

C4 and C3 Pathways - Effect of CO2 concentration Competitive advantage between C3 and C4 switches along CO2 gradient Low CO2: C4 advantage due to concentrating of CO2 Ambient CO2: net growth about equal but water use is greater in C3 High CO2: C3 advantage due to C4’s low CO2 saturation point and reduction of CO2 / O2 conflict in C3 C3 60 50 C4 40 700 ppm CO2 30 Net Photosynthesis (µmol m-2 s-1) 350 ppm CO2 200 ppm CO2 20 10 -10 100 200 300 400 500 600 Intercellular CO2 (ppm)

PS Pathways - Further Reading Polley, H.W. 1997. Implications of rising atmospheric carbon dioxide concentration for rangelands. Journal of Range Management. 50:561-577. Pearcy, R.W., and J Ehleringer. 1984. Comparative ecophysiology of C3 and C4 plants. Plant. Cell and Environment. 7:1-13. Data presented in this slide set were adopted from these 2 sources. They are both excellent resources.