Drought stress is one of the most yield-limiting factors worldwide in agriculture and horticulture. Due to climate change, periods of water shortage are becoming more frequent, more intense, and harder to predict. Drought not only affects growth but also disrupts fundamental processes such as photosynthesis, nutrient uptake, and cell stability.

Biostimulants against drought stress are therefore becoming increasingly important as a preventive cultivation strategy. Instead of correcting drought only when damage becomes visible, biostimulants physiologically support the plant in advance via osmoregulation, root activation, and stress priming.

What happens in plants under drought stress?

When soil moisture decreases, the water potential around the root drops. Plants then have difficulty absorbing water, leading to a cascade of stress responses:

• reduced cell elongation and growth inhibition
• closure of stomata and lower CO2 uptake
• decline in photosynthesis and energy availability
• disrupted transport of nutrients
• increase in oxidative stress due to ROS

Drought stress is therefore not just “too little water”, but a systemic disruption of plant physiology.

Osmoregulation: turgor maintenance as a core mechanism

One of the plant's first lines of defense is cellular osmoregulation. Plants accumulate so-called osmolytes to retain water and maintain internal turgor pressure.

Important osmoprotective substances include:

• glycine betaine
• proline
• sugar alcohols

Biostimulants that support osmoregulation help plants remain functional longer under water shortage.

Root activity as the basis for drought tolerance

Drought resistance almost always starts in the root zone. A powerful root system increases the exploration volume in the soil, allowing plants to use water from deeper or less accessible layers.

Biostimulants stimulate root development via:

• formation of lateral roots
• increase in root hairs
• improved rhizosphere activity
• higher uptake efficiency of water and minerals

This greatly increases functional drought tolerance, even without additional irrigation.

Stress priming: being prepared before drought occurs

One of the most valuable biostimulant concepts is plant priming. Priming means that the plant develops an increased stress readiness in advance, allowing responses to occur faster and in a more controlled way when drought strikes.

Primed plants show:

• faster osmolyte accumulation
• more efficient antioxidant response
• less growth loss under stress pressure

Oxidative stress and ROS neutralization

Drought stress almost always causes increased production of ROS (reactive oxygen species). When ROS accumulate, damage occurs to membranes, chloroplasts, and enzymatic systems.

Biostimulants therefore often enhance the activity of antioxidant enzymes, such as:

• superoxide dismutase (SOD)
• catalase
• peroxidases

This enhanced ROS neutralization stabilizes photosynthesis and cell integrity.

Important biostimulant raw materials against drought stress

Seaweed extracts

Brown seaweed extracts support priming, osmoprotection, and root continuity under stress. Polysaccharides and phenols provide both signaling effects and antioxidant capacity.

Osmoprotectants

Substances such as proline and glycine betaine support direct osmotic buffering and turgor maintenance.

Silicon

Silicon strengthens cell walls and reduces transpiration losses, enabling plants to use water more efficiently.

Fulvic chelation

During drought, nutrient mobility decreases. Fulvic acid keeps micronutrients soluble and supports uptake and transport.

From stress to yield security

The goal of biostimulants against drought stress is not only survival, but maintaining productivity. Through root activity, osmoregulation, and antioxidant protection, this results in:

• more uniform growth under water shortage
• faster recovery after stress moments
• less loss in fruit set and quality
• more stable yield and production security

Overview: biostimulant strategies under drought stress