Plant Adaptations: Photosynthesis and Productivity

• Plant adaptations are covered.
• Focus on photosynthesis, productivity, and adaptations to limiting factors like light, water, temperature, and nutrients.

How Plants Make a Living

• Life is based on carbon atoms, mainly from CO2.
• CO2 becomes organic via autotrophs.
• Chemoautotrophs derive energy from oxidizing inorganic molecules.
• Photoautotrophs get energy from the sun via: 6CO2 + 6H2O (+ Sun's energy) -> C6H12O6 + 6O2

Photosynthesis: Converting CO2 to Sugars

• Photosynthesis has two stages: light and dark reactions.
• In light reactions, chlorophyll absorbs light energy, turning it into ATP and NADPH.
• Dark reactions involve using ATP and NADPH to incorporate CO2 into simple sugars.
• The amount of ATP and NADPH from light reactions can limit dark reactions.
• Carbon fixation depends on the enzyme rubisco.

Calvin-Benson Cycle (C3 Cycle)

• The Calvin-Benson cycle, also known as the C3 cycle, initially fixes CO2 into a 3-carbon molecule.
• Rubisco can react with O2, reducing photosynthetic efficiency and releasing CO2.

Respiration and Net Photosynthesis

• Respiration uses photosynthetic products.
• Cellular respiration equation: C6H12O6 + 6O2 -> 6CO2 + 6H2O + ATP.
• Anaerobic respiration (fermentation) occurs without oxygen: C6H12O6 -> 2C3H6O3 + 2 ATP.
• Net photosynthesis is photosynthesis minus respiration, measured in moles of CO2 per unit leaf area (or mass) per unit time.

Light and Photosynthetic Activity

• The relationship between light and photosynthetic activity includes:
• A maximum rate of net photosynthesis.
• A light compensation point where the plant gains as much carbon as it loses to maintain growth.
• A light saturation point.
• The rate of respiration.

Photosynthesis Exchanges

• C3 photosynthesis takes place in mesophyll cells, needing CO2 and H2O.
• CO2 enters leaves through stomata.
• O2 and H2O exit through the stomata.

Stomata and Transpiration

• Plants regulate stomata opening and closing.
• Transpiration is water loss through stomata.
• H2O movement depends on a diffusion gradient, maintained by water evaporating from leaves.
• Water lost via transpiration must be replaced to maintain turgor pressure.

Water Movement and Potential

• A diffusion gradient drives transpiration.
• Water potential measures water's free energy, establishing this gradient.
• Pure water has the greatest free energy (0 MPa).
• 100% relative humidity = 0 MPa.
• Water moves from more positive to negative water potential areas. Transpiration from leaf to atmosphere is typical but reversible.

Transpiration Dynamics

• Transpiration still occurs as follows: atm < leaf < root < soil.
• During drying, water potential in the soil declines, which requires a corresponding decline in water potential in the root and leaf to maintain the gradient.

Factors Affecting Water Loss

• The rate of water loss varies with humidity, temperature and plant characteristics (stomata closing and opening).
• Water use efficiency is the ratio of carbon fixed to water lost.
• Terrestrial plants balance CO2 intake with water loss and risk desiccation.

Photosynthesis vs. Stomata

• Tradeoffs must be made to maintain photosynthesis and closing stomata.
• Species curves indicate habitat and balance net photosynthesis with water loss.

Plant Adaptations

• Plant adaptations balance access to limited resources and carbon allocation for:
• H2O
• Temperature
• Light (PAR)
• CO2
• Minerals

Fog and Coastal Redwoods

• Redwoods have high potential for water loss with LAI and stomatal control.
• Fog helps to compensate for water loss.
• They thrive where there are wet winters with foggy summers.
• High sap flow and evapotranspiration (ET) are seen in summer.
• Water losses are high, even at night, relative to summer maximum.
• Fog contributes significantly. 30+% of water input comes from canopy drip
• Fog slows water loss via stomata through reduced stomatal conductance.

Foliar water uptake

• 6% of leaf water comes from previous night's fog by foliar uptake
• Isotopes were used in experiments involving fog, with data collected regarding young and old leaves.

Temperature's Effects

• Photosynthetic rate is limited by the rubisco reaction's to temperature.

Water, Temperature, and Plant Adaptations

• Water demand is linked to temperature.
• Plants balance opening and closing stomata, affecting H2O loss and CO2 gain.
• Closing stomata reduces evaporative cooling.
• Photosynthesis decreases while leaf temperatures rise, requiring stomata to open to cool rubisco.

Plant Responses to Stress

• Plant responses to moisture stress include:
  • Leaf curling.
  • Inhibiting chlorophyll production.
  • Drought deciduousness.
  • Modified photosynthetic pathways.

Photosynthetic Pathways

• Plants in warmer, drier areas use photosynthetic pathways, increasing water-use efficiency.
• C4 photosynthetic pathway found in tropical grasses.
• CAM pathways found in desert succulents.

C4 Photosynthesis

• C4 photosynthesis separates CO2 fixation in separate areas
• Increases efficiency because rubisco isn't interacting with oxygen.
• Plants fix carbon, which hasbundle sheath cells.

CAM Photosynthesis

• CAM separates CO2 fixation temporarily, and stoma open at night to lower water loss.

Leaf Modifications

• Further modifications minimize water loss.
• Small Leaf size.
• Thick cell walls.
• Small stomata.
• Dense vascular systems.
• Hairs, wax, and resins.

Acclimation and Adaptation

• Plants show adaptations and acclimation to temperature variations.
• Plants in cooler areas have lower Tmin, Topt, and Tmax for photosynthesis. Temperature responses are not fixed but adapt to their developing conditions.

Survival Adaptations in Temperate Climates

• Plants that are native to to temperate environments have adaptations for survival.
• Frost hardening is a conversion of cells into cold sensitive ones.
• Forming/adding protective compounds such as antifreeze.
• Drop leaves during the winter/Winter deciduous.

Light Environments

• Sun plants versus shade plants. Shade-tolerant plants tend to have lower compensation and saturation levels. This is because investing In rubisco is a tradeoff.

Plant Adaptations to Light

• Phenotypic plasticity is where is a photosynethic and morphological response.
• This accounts to leaves on a plant with different levels of light.

Individuals and Shade

• Individuals growing up in the shade have different adaptations. A lower amount of leaf respiration. Greater special leaf area and allocate loss of carbon to leaf production.

Nutrient Availability

• Availability of nutrients is important for survival, growth, and reproduction. Nitrogen in particular is important
• Adaptations include Maximum, Leaf longevity and increased root mass
• Plant have adaptations to reach good photosynthesis if nutrients are low.

Wetland Conditions

• Wetland conditions can cause poor adaptations for plants because water can be stress plants
• If soil is heavily saturated it cause anareobic respiration
• If there are is anareobic or flooded conditions, plants response. Plants roots die and the adventitious roots emerge above.
• Develop shallow root systems, or Pneumatophores= growths of the root systems.