7A_Plants and the Environment
PLANTS and the ENVIRONMENT
Environment
Definition: The complex of climatic, edaphic, and biotic factors that affect organisms.
Determines the form and survival of living entities.
Ecology
Definition: The science dealing with reciprocal relations between organisms and their environment.
Plant Ecology: Focuses on the relationship between plants and the physical, biotic, and physiological aspects of the environment.
Physiological Ecology: Studies how plants grow within their natural environment.
Plant Ecosystems
Definition: Dynamic aspects of vegetation, flora, and environmental factors.
Vegetation: The types of plants that survive in a region based on climatic and environmental limitations.
Flora: Actual species of plants that constitute the vegetation of a region.
Levels of Organization in Ecology
Organism (physiological)
How an individual meets the challenges of its physical and chemical environment.
Population
A group of individuals of the same species in a specific geographic area.
Community
An assemblage of populations from different species inhabiting a location.
Ecosystem
Includes abiotic (non-living) factors and the community of species in a specific area.
Biosphere
The part of Earth containing all ecosystems.
Key Concepts in Ecology
Saturation Concept
Utilization of a factor (resource) until capacity is reached.
Dose-response Curve:
Deficiency Zone: Increased response.
Tolerance Zone: No change in response.
Toxicity Zone: Decreased response.
Limiting Factor Concept (Liebig’s Law of the Minimum)
Plant growth depends on the minimum quantity of resources (or "foodstuff") available.
Limiting factors: Mineral nutrients, water, pest damage, weed competition, CO2 levels, genetics.
Interaction of Factors
Synergism: Combined response is greater than the sum of individual effects.
Additive: Different factors contribute to causation without interaction.
Multiplicative: Different steps in the causal sequence interact.
Environmental Influences on Plants
Climate impacts requirement for nutrients, water, energy, and resistance to harmful factors.
Humidity may compensate for low rainfall; one factor can predispose plants to a harmful condition.
Example: Rice plants grown under diffuse light may become weak and susceptible to disease.
Disturbance and Response Dynamics
Disturbance of one environmental factor can lead to cascading changes.
Example: Fertilization can enhance dominant species growth, causing environmental changes like shading.
Synergism vs. Antagonism: Interaction that may yield unexpected results.
Categories of Plant Response
Direct (non-delayed): Immediate changes as the environment shifts (e.g., photosynthesis).
Triggered (on-off): Starts when a threshold is crossed; response may continue post-threshold (e.g., germination).
Modulated, Delayed: Response level depends on the extent of environmental factor, may involve biological clocks (e.g., phototropism).
Conditioning Effects: Gradual change with ongoing exposure (e.g., drought resistance).
Homeostasis: Maintenance of internal conditions despite environmental changes.
Carryover Effects: Growth conditions affecting future generations (e.g., experiments with inbred pea plants).
Environmental Factors and Their Effects
Water
Even rainfall distribution supports diverse vegetation; concentrated rainfall leads to less diversity.
Temperature
Extreme temperatures can halt growth, cause chlorosis, or lead to death; seasonal variations affect growth patterns.
Light
Plants vary in sun and shade preferences.
Soil
Factors include soil pH, moisture, aeration, salinity, and microorganisms.
Atmosphere
Flora can be altered by natural and man-made pollution, such as sulfur dioxide (SO2).
Genetics
Ecophenes: Plants sharing genetic make-up but exhibiting morphological and physiological differences.
Ecotypes: Genetic variations found across different areas of a species distribution.