Transpiration in Plants

Transpiration in Plants

• Transpiration is the loss of water from plants in the form of water vapor.
• Phases include evaporation from mesophyll cells and diffusion into the atmosphere.
• Temperature and relative humidity influence transpiration rates.
• Wind increases transpiration by replacing humid air around leaves with drier air.
• Soil moisture availability impacts transpiration rates.
• Plant type (e.g., arid-adapted plants) affects transpiration rate.

Stomatal Functions

• Stomata, controlled by guard cells, regulate water loss and gas exchange.
• Guard cells swell open when turgid; they close when flaccid.
• 80-90% of water loss in plants occurs via stomata.
• Additional water loss occurs via the cuticle, and 1-5% via lenticels.

Importance of Transpiration

• Regulates water movement in plants.
• Provides water for photosynthesis.
• Transports minerals from roots to leaves.
• Cools the plant through evaporation.
• 3,000-4,000 gallons of water can be transpired by an acre of corn daily.
• A large oak tree can transpire 40,000 gallons annually.

Photosynthesis

• Photosynthesis is the process of converting light energy into chemical energy to produce carbohydrates.
• It takes place in cells, primarily in the leaves.
• Photosynthesis has light-dependent and light-independent (Calvin Cycle) reactions.
• Light reactions occur in thylakoids, splitting water into O2 and H+ producing ATP and NADPH.
• Light-independent in the stroma, fixing CO2 into carbohydrates.

Radiation Use Efficiency (RUE)

• RUE is the efficiency of converting PAR into biomass.
• PAR (Photosynthetically Active Radiation) is the wavelength of radiation that plants use.
• 400-700nm wavelength.
• Under agricultural conditions, 0.1-3% of radiant energy is converted into organic matter.

C3 and C4 Photosynthesis

• C3 plants fix CO2 via Rubisco, and are susceptible to photorespiration (inefficient process).
• C4 plants fix CO2 via PEP carboxylase, which minimizes photorespiration, resulting in higher water-efficient performance.
• Plants like wheat, rice, and soybean are C3, while maize, sugarcane are C4.

Leaf Area Index (LAI)

• LAI is a measure of total green leaf area per unit ground area.
• LAI is important to capture light because a leaf canopy affects the amount of light that reaches the soil
• Higher LAI values result in increased light interception leading to increased photosynthetic rates and crop yield.
• LAI is controlled by phyllochron, timing of crop emergence, and leaf expansion rate.

Photosynthesis and Translocation

• Photosynthesis and product movement are simultaneous processes.
• Excess photosynthates are stored for later use, transported by phloem and plasmodesmata.
• Plants use 70-80% of photosynthates within 6 hours of photosynthesis
• C4 plants generally have faster rates of translocation due to specialized structures.

Factors Influencing Plant Yield

• Temperature, nitrogen availability, solar radiation, water supply, plant density, pests and diseases are key factors.
• Optimal temperature ranges exist for different crops and varieties.
• Nitrogen is critical for chlorophyll formation and leaf expansion.
• Water stress can reduce leaf size, and longevity affecting LAI.

Strategies for Maximizing Yield

• Strategies to maximize yield include improving light interception, adapting to water stress, using optimal population densities, and minimizing the effects of disease, pests, and weeds.