Plant water relations notes part 2

Effects of Water Deficits on Plants

• Physiological Effects

  • Stomatal closure leads to reduced gas exchange
  • Nonstomatal effects negatively impact photosynthesis

• Growth & Morphological Effects

  • Reduced cell turgor results in decreased growth and cell division
  • Increase in root:shoot ratio
  • Other morphological adaptations may occur

• Effects on Reproduction & Fitness

  • Complex interactions; impacts may vary
  • Plasmolysis as a significant concern for cellular integrity

Evolutionary Responses to Water Availability

• Xerophytes

  • Adapted to dry environments with limited water

• Mesophytes

  • Adapted to adequately moist environments

• Hydrophytes

  • Adapted to wet or aquatic environments with abundant water

Drought Resistance Adaptive Strategies

• Drought Escape

  • Life cycle completed before drought onset (e.g., annual plants)
  • Perennial species can enter drought-induced dormancy

• Drought Avoidance

  • Mechanisms prevent tissue desiccation and maintain viable water potentials

• Drought Tolerance

  • Mechanisms for maintaining physiological processes under low water conditions

Drought Avoidance Mechanisms

• Anatomical and Morphological Adaptations
  • Reduction of leaf area to minimize water loss
  • Development of photosynthetic stems
  • Leaf folding or rolling to reduce surface area exposed to the atmosphere
  • Thick cuticles and waxes for protective barriers
  • Presence of epidermal hairs and sunken stomata to reduce transpiration

Leaf Adaptations in Grasses

• Leaf Folding and Rolling
  • Illustrated with the bulliform cells in grasses

Enhanced Water Use Efficiency (WUE)

• Instantaneous WUE

  • Calculated from Photosynthesis (P) relative to Transpiration (T)

• Time Integrated WUE

  • Assessed using carbon isotope ratios (δ13C) in C3 plants
  • Stomata closure leads to lowered internal carbon (Ci), influencing RUBISCO activity

• Higher δ13C corresponds to greater WUE

Root Systems in Water Uptake

• Importance of root length and distribution
  • Deep Roots tap into reliable, deeper water sources
  • Phreatophytes capitalize on groundwater access
  • Shallow Roots capture more variable moisture from surface rainfall

Drought Tolerance Strategies

• Surviving Low Water Potentials
  • Enzymes facilitate desiccation tolerance
• Turgor Maintenance
  • Osmoregulation through accumulation of proline and other compounds
  • Cellular elasticity aids in maintaining structure despite water loss

Plant Water Cycle Interaction

• Ecohydrology
  • Water movement through the ecosystem highlighted by various pathways such as evaporation, transpiration, and percolation
  • Understanding plant-water interactions is crucial for managing water resources

Deforestation and Water Cycle Impact

• Deforestation in Amazonia may reduce seasonal rainfall up to 21% due to loss of moisture recycling
• Tropical forests are crucial for atmospheric water recycling through high rates of transpiration and condensation

Human Influence on Vegetation and Water Yield

• In arid regions, vegetation manipulation is used to enhance water yield
• Clearing brush may not always lead to increased groundwater recharge; variability in outcomes noted

Conclusion

• Climate and vegetation changes due to human activity are significantly affecting the hydrologic cycle on multiple scales.