What is Drought Stress?

Drought stress is metabolic stress that occurs when water in the soil is reduced or exhausted by evaporation, lack of watering, and/or from use in photosynthesis. Most plants have some level of tolerance to drought stress. Many plants respond to water stress by altering the allocation of nutrients for biomass production. An example of this is when the plant increases growth to shoots or roots as a coping strategy, altering its appearance.

What Drought Stress Does to Plants

As a result of biomass reallocation and decreased overall production, total crop yields can decline from drought stress. Even moderate loss of water limits gas exchange and leads to stomatal pore closure (stopping transpiration), lower leaf water potential, and lower total plant water content, wilting, and decreased growth. Extensive water loss may severely disturb metabolic processes, leading to cell structure changes. Desiccation (complete drying out) may lead to a complete cessation of photosynthesis, major metabolic disruptions, and plant death.

Effects of Drought Stress

• Plant growth may be reduced via physiological and biochemical process disruption (photosynthesis, respiration, translocation, ion uptake, carbohydrates, nutrient metabolism, and hormone production).
• Plant appearance is influenced by reduced cell elongation and expansion, leading to reduced stem length and plant height. 
• Osmotic regulation/turgor pressure may be disturbed and results in leaf death and reduced leaf growth in size (decreased leaf size = decreased area for absorbing light and CO2/O2 respiration).
• Some plants increase or decrease root growth as a response to combat varying levels of water scarcity.
• The type of drought stress effect and degree of effect varies by plant species.
• Plants with better root systems can extract water from deeper soil which combats drought due to evaporation. Shallow root systems are limited to the water available in the upper soil that is more prone to evaporation.

Irrigation is vitally important to plant quality and quantity. Once a plant is visibly wilted, the effects of that drought stress cause permanent damage to the plant. Plants can be revived from a wilted state, but ultimately they will not be as productive as a plant that has never reached that point of stress. Water supply and quality directly influence yield and determines how successful your crop will be.