Effect of water deficit on physio-morphological characteristics of the plants
Water deficit, or drought stress, significantly affects the physio-morphological characteristics of plants, influencing their growth, development, and productivity. Here are the main effects:
- Water Relations:
- Reduced Water Absorption: Water deficit impairs root water uptake, leading to decreased turgor pressure and wilting.
- Transpiration and Stomatal Closure: Plants close stomata to minimize water loss, which reduces transpiration but also limits CO₂ intake, affecting photosynthesis.
- Photosynthesis:
- Reduced Photosynthetic Rate: Due to stomatal closure, reduced CO₂ availability decreases the photosynthetic rate.
- Chlorophyll Degradation: Drought can lead to chlorophyll breakdown, reducing light absorption for photosynthesis.
- Photorespiration Increase: Under stress, oxygenation of RuBP increases, leading to more photorespiration and reduced carbon fixation.
- Respiration:
- Mild Drought: Increases respiration due to energy requirements for stress response.
- Severe Drought: Lowers water content and reduces respiratory activity, affecting energy production.
- Growth and Development:
- Leaf Growth: Decreased leaf area and leaf expansion due to reduced cell turgor and division.
- Stem and Root Growth: Shoot growth is more affected than root growth. Roots may grow deeper to access moisture.
- Fruit and Seed Development: Reduced size, number, and weight of fruits and seeds due to limited nutrient and water supply.
- Hormonal Changes:
- Abscisic Acid (ABA): Increases during water stress, leading to stomatal closure and growth inhibition.
- Cytokinins and Gibberellins: Decrease, reducing cell division and elongation.
- Ethylene Production: Increases, promoting leaf senescence and abscission.
- Anatomical Changes:
- Cell Size: Decrease in cell size and intercellular spaces.
- Cell Wall Thickness: Increased cell wall thickness for structural support under low turgor.
- Stomatal Density: Stomatal density per unit leaf area may increase to maximize gas exchange when open.
- Metabolic Reactions:
- Reduced Enzyme Activity: Water deficit affects enzyme structure and function, altering metabolic pathways.
- Protein Synthesis: Decreased due to energy limitations and oxidative stress.
- Lipid Peroxidation: Enhanced oxidative stress leads to membrane lipid degradation.
- Nutrient Uptake and Assimilation:
- Nutrient Transport: Reduced transpiration affects nutrient uptake and transport.
- Nitrogen Fixation: Limited in legumes due to impaired symbiotic nitrogen-fixing bacteria.
- Yield and Productivity:
- Biomass Reduction: Decreased total biomass due to reduced photosynthesis and growth.
- Yield Loss: Significant yield reduction in crops, especially if drought occurs during reproductive stages (flowering and grain filling).
- Adaptations and Responses:
- Morphological Adaptations: Smaller leaves, thicker cuticles, and deep rooting systems.
- Physiological Adjustments: Accumulation of osmolytes (proline, glycine betaine) for osmotic adjustment.
- Biochemical Responses: Enhanced antioxidant enzyme activities to combat oxidative stress.
Early Indicators of Drought in India
Kharif Season Indicators:
- Delay in Onset of Southwest Monsoon: Indicates late planting and reduced crop yields.
- Prolonged Dry Spells: Interrupt crop growth and reduce productivity.
- Rise in Fodder Prices: Reflects scarcity and increased livestock maintenance costs.
- Slow Reservoir Recharge: Impacts irrigation and water availability.
- Drying of Rural Drinking Water Sources: Affects both human and livestock water supply.
- Decline in Sowing Progress: Indicates farmers’ hesitation to invest due to uncertain rainfall.
Rabi Season Indicators (November to January):
- Deficient Southwest Monsoon Rainfall: Reduces soil moisture, impacting winter crops.
- Groundwater Depletion: Low water table affects irrigation and drinking water supply.
- Low Reservoir Levels: Indicates poor recharge, affecting irrigation during Rabi.
- Soil Moisture Stress: Affects germination and growth of Rabi crops.
- High Fodder Prices: Reflects scarcity due to poor Kharif yields.
- Increased Water Supply via Tankers: Indicates severe water scarcity in affected regions.
Other Seasonal Indicators:
- Chronic Hydrological Drought: Common in Gujarat, Central Maharashtra, Marathwada, and North Karnataka, leading to drinking water scarcity.
- Lack of Rain in February: Affects plantation crops in Kerala, impacting productivity.
