Ecology of Photosynthesis II The Light Compensation Point PPFD = Photosynthetic Photon Flux Density Ecology of Photosynthesis Measuring CO 2 Fluxes Individual Plant Measuring CO 2 Fluxes Community Level Photorespiration: A curious bottleneck in C3 Photosynthesis Key enzyme 3-carbon compound Catalysis of carbon fixation in Photosynthesis Photorespiration: An alternate pathway Rubisco Rubisco catalyzes two competing reactions: Photosynthesis Photorespiration Ecological Factors Increasing Photorespiration Rates Rubisco High temperatures Low CO 2 concentrations The Stomate as a Bottleneck Under Water Stress CO 2 O2O2 H2OH2O C 4 Photosynthesis: A Solution in Space C 4 Grass C 3 reactions throughout C 3 reactions in bundle sheath C 3 Grass C 4 Photosynthesis: A Solution in Space C 4 Intermediates produced in low CO 2 environment of mesophyll ( : 1 CO 2 ) CO 2 concentrated in bundle sheath ( : 1 CO 2 ) Differential Response of C 4 and C 3 Plants Temperature response Light response CAM Photosynthesis: A Solution in Time CO 2 Capture by NightPhotosynthesis by Day CAM Photosynthesis: A Solution in Time Distribution Patterns of the Three Photosynthesis Types Geographic Patterns in the Distribution of the Proportion of C 4 Grasses Higher temperatures Higher total rainfall Higher summer rains C 3 Cool Season Grasses Lower temperatures Lower total rainfall Higher winter rains C 4 Warm Season Grasses Habitats Favoring CAM Plants Epiphytes Plants using other plants for support Arid habitats deserts and semi-deserts that arent too extremely dry Ecology of Photosythesis Part III Sun and Shade Leaves Sun Shade Anatomy of Sun and Shade Leaves (Thermopsis montana): a general view Sun LeafShade Leaf Smaller Thicker More rubisco More chlorophyll Bigger Thinner Less rubisco Less chlorophyll Sun and Shade Leaves: Response to Light (Fagus sylvaticus) Light capture and leaf orientation Ecology of Water Relations Water Potential ( and the Dynamics of Water Movement Direction of water movement Dry conditions Wet conditions What the heck is water potential ( ? p m g osmotic potential is zero in pure water and less than zero in water with solutes Leads to movement of water into cells p pressure potential is caused by the resistence to volumetric expansion p m g xylem cell Pressure potentials in plant tissues can be negative or positive, depending on the water status of tissues p m g m matric potential is the result of cohesive forces that bind water to physical objects; always negative Matric potentials are important in soils, not in plants p m g g gravitational potential is the result of the pull of gravity on water; negative when flow of water is downwards Gravitational potentials are important in soils, not in plants Measuring Pressure Potentials in the Field Transpiration and Water Movement Control of Water Loss Stomates