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Upcoming Seminars: EECB seminars – 4:00 Thurs in OSN 102

Upcoming Seminars: EECB seminars – 4:00 Thurs in OSN 102 Thurs Feb 5: Jed Sparks (Cornell) “ Vegetation-level process controls on troposhperic chemistry ” Geography seminar – 4:00 Wed in Mackay Science 215.

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Upcoming Seminars: EECB seminars – 4:00 Thurs in OSN 102

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  1. Upcoming Seminars: • EECB seminars – 4:00 Thurs in OSN 102 • Thurs Feb 5: Jed Sparks (Cornell) “Vegetation-level process controls on troposhperic chemistry” • Geography seminar – 4:00 Wed in Mackay Science 215. • Wed Feb 4: Alan Taylor (Penn State) “presettlement Forests, Fire Regimes, and Climatic Influences in the Tahoe Basin”

  2. Outline • Radiation: heat, light, and photosynthesis • Energy budgets • Energy capture and dissipation • Photosynthesis: Calvin cycle, photorespiration • Alternative photosynthetic pathways • Carbon accumulation, ecological implications

  3. Radiation (electromagnetic waves) • Short wave (solar radiation) <4um wavelength • UV 10-400nm (@ Earth’s surface 292-400) • Potentially damaging to biological systems • Visible 400-700nm • Source of most energy for life on earth • Near infrared 0.7-4.0um (and far red visible) • “shade detector” pigment phytochrome absorbs 660nm and 730nm • Can cause inhibition of germination etc. • Long wave: far IR; heat. • Heat is energy from objects (molecular motion).

  4. Energy budgets • Energy cannot be created or destroyed • Net=met+solar+thermal+conv+cond+LE+storage • Plants absorb PAR and reflect or transmit non-PAR • Use only a fraction of energy absorbed (2%); must dissipate the rest • Angle of incidence determines energy intercepted. • Paraheliotropic=leaf parallel to sun’s rays • Diaheliotropic=leaf perpendicular to sun’s rays • Sun VS shade leaves: different morphology • Albedo, laminar flow, reduced leaves

  5. Energy effects • Light or temperature mediated plant responses: • Germination/seed dormancy (light) • Thermoperiodism (buds, seeds) temp differential induces dormancy or activity • Dormancy – end of dormancy triggered by photoperiod or temperature • Temperature stratification of seeds (hot or cold) • Physical rupture of seed coat (fire)

  6. Energy capture: photosynthesis • Leaves absorb light between 400 and 700nm • Energy is captured through an electron transfer chain (“light reactions”) • Carbon dioxide is fixed into carbohydrate (“dark reactions”) using energy captured in light reactions • Calvin cycle (C3) prone to photorespiration (light-mediated release of CO2) • Level of photorespiration depends on CO2:O2

  7. Electron transport

  8. Calvin cycle

  9. C4 Photosynthesis • Means to concentrate CO2 and reduce photorespiration. Requires energy (ATP) and special anatomy (Kranz) • CO2 fixed in mesophyll cells to form a 4-carbon acid (oxaloacetate) • C4 chain diffuses to bundle sheath cells, releases CO2, C fixation occurs ‘normally’. • Higher light compensation point than C3, and greater water use efficiency.

  10. CAM Photosynthesis • Temporally separates light and ‘dark’ reactions • Succulents • At night stomata open; plants fix CO2 to malic or isocitric acid (4-carbon). Uses ATP. • Acid stored in large cell vacuole. • During day stomata close, CO2 released, and fixed in “C3 type fixation” • Plants with this pathway are not always obligate CAM – can switch to C3.

  11. Environmental differences • CO2 compensation lower for C4 than C3 (can have higher stomatal resistance and still fix C) • Light saturation higher for C4 than C3 (reduced photorespiration) • Light use efficiency highest for C4 monocots. • C4 uses energy; less efficient at lower light and temperatures • Water stress: C4 more efficient than C3, CAM can switch to C3 (less energy) when water available

  12. Ecological implications • Timing of rainfall and nutrient availability affect composition. How? • What are differences in radiation impacts in forest VS rangeland? • What would effects of global climate change and CO2 enrichment be? • How might plants with different photosynthetic pathways be distributed?

  13. Ecological implications • Timing of rainfall and nutrient availability affect composition. N availability affects photosynthetic rates. • Herbivory and “overcompensation” – dependent on N availability? • What are differences in radiation impacts in forest VS rangeland? • What would effects of global climate change and CO2 enrichment be?

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