16: Climate Change + the Impact on Plants

• Global warming: increase in average temperature of the planet
• Climate change: sum of all changes in local temperature + precipitation patterns resulting from global warming
• Climate: long-term average pattern of regional or global weather
• Weather: short-term, highly variable atmospheric conditions at a specific place and time
• Temperatures in polar regions will increase more than tropics
• Some ecosystems at the same latitude will experience higher temperature increase due to wind patterns + ocean currents
• Despite warming, some areas will experience extreme freezes in the winter and/or more extreme heat waves in the summer

  • Critical effect on ecosystems and ability of species to survive
• Precipitation will become more variable + change patterns
• Positive Feedback: changes due to global warming result in further acceleration of warming

  • Warmer, drier climate increases forest fires, which release more CO2 --> more warming
  • Tundra sequesters C in the form of soil organic matter
  • During warm summers, decomposition rates increase enough to release stored C
  • When polar ice caps melt, it exposes more open water which reflects sunlight less than ice, increasing warming of oceans and the planet
• Negative Feedback: changes due to global warming result in increased uptake + sequestration of CO2 + other greenhouse gases

  • Growth rate of several tree species + plants increase in direct response to increasing atmospheric CO2, storing C in plant organic matter
• Leaves absorb about 50% of total solar radiation:

  • Absorbed light
  • Radiated heat loss
  • Convection heat loss (sensible heat loss)
  • Evaporative cooling
• Bowen ratio: sensible heat loss/ evaporative heat loss

  • When water is available, Bowen ratio is low
• Transpiration removes heat from plants by evaporative cooling:

  • Access to water is required
  • Photosynthesis is temperature-sensitive
• Maximum photosynthesis occurs in a narrow temperature range:

  • Species-dependent
  • Adapted to environment
• C4 plants have optimal photosynthetic rates at higher temperatures than C3 plants
• Temperature affects:

  • Enzyme activity
  • Respiration rate
  • Chloroplast membrane integrity
  • High temperature uncouples electron transport process
• C3 plants: increasing temperature decreases affinity of rubisco for CO2 + photorespiration increases
• C4 plants: leaves saturated with CO2 + negative effects of higher temperature on rubisco is not observed

  • Have a competitive advantage at higher temperatures
• C4 plants: photosynthetic rates saturate at intercellular CO2 concentration of 100-200 ppm
• C3 plants: increasing CO2 concentration stimulates photosynthesis over a larger range

  • Most C3 plants grow 30% faster when CO2 reaches 600 ppm
  • Require access to water and nutrients
  • Will see increased photosynthetic rates as CO2 levels rise
• CAM plants:

  • Adapted to hot, dry conditions
  • Temporal separation of CO2 acquisition and CO2 fixation
  • Stomata are open at night, reducing transpiration water loss
  • Under changing precipitation patterns, CAM plants will outcompete in desert environments
• CAM idling permits survival under extreme water stress

  • Stomata are closed day and night
  • Permits survival in extreme drought
• Geographic Range Shifts: the geographic redistribution of species to more favourable climate envelopes can change ecological interactions
• Mountain Pine Beetles (MPBs):

  • First MPB to attack tree releases a chemical signal called an aggregation pheromone that recruits other beetles, allowing them to join forces to overcome the host tree's defenses
  • Female MPB gets into the layer of vascular cambium, where she releases a mating pheromone + lay eggs
  • When eggs hatch, they eat their way through the vascular cambium (cutting off transport of water + minerals to leaves)
• Mountain Pine Beetles (MPBs) are helped by a blue-stain fungus the adult beetle actively gather + spread:

  • Blue-stain fungi invade host's phloem and xylem, damaging or killing the tree + also serve as additional food for the beetle
• Oceans:

  • Absorb 1/3 of global CO2 emissions
  • When CO2 dissolves in water, it forms carbonic acid causing ocean acidification
  • Difficult for marine animals to maintain shells + skeletons made of calcium carbonate
  • Aquatic plants may pull CO2 from oceans, reducing acidity