Heat, Drought & Salinity Stress: What Biostimulants Can — and Cannot — Do

Abiotic Stress vs Biotic Stress

Abiotic stress comes from non-living conditions such as drought, salinity, heat, cold or waterlogging. Biotic stress comes from living agents such as insects and pathogens. This distinction matters because supporting plant stress physiology is not the same as controlling an insect, fungus or bacterium.

What Happens Inside a Plant Under Abiotic Stress?

Different stresses start from different causes, but several downstream effects can overlap: disrupted water status, lower photosynthetic efficiency, altered ion balance, membrane damage and changes in reactive oxygen species. The severity depends on crop, growth stage, stress intensity, duration and the plant’s previous condition.

What Is Osmotic Stress?

Osmotic stress means the plant has difficulty maintaining water balance even when water may be physically present around the roots. Drought can reduce available water, while salinity lowers the water potential around roots. Plants respond through changes in stomata, compatible solutes, root behaviour and metabolism.

ROS, Oxidative Stress and the Antioxidant System

Reactive Oxygen Species (ROS) are normal signalling molecules at controlled levels, but excessive accumulation can damage lipids, proteins and cellular structures. Plants use enzymatic and non-enzymatic antioxidant systems to keep ROS in balance. Scientific reviews show that several biostimulant categories can influence redox and antioxidant responses under stress, but the effect is formulation- and crop-dependent.

Why Photosynthesis Can Fall Under Heat, Drought or Salinity

Stress can reduce stomatal opening, carbon dioxide entry, chlorophyll function and the efficiency of photosynthetic machinery. A formulation that supports root water relations, nutrient status, osmotic adjustment or antioxidant balance may indirectly help preserve photosynthetic performance, but this should not be converted into a universal “photosynthesis booster” claim.

Where Biostimulants May Support the Stress Response

• Root development or root activity that can improve soil exploration.
• Osmotic adjustment and compatible-solute related processes in some biostimulant categories.
• Antioxidant and redox-balancing processes that help limit oxidative damage.
• Photosynthetic and metabolic stability under moderate stress in some crops/formulations.
• Nutrient uptake or assimilation where stress is limiting root or metabolic function.

Amino Acids and Protein Hydrolysates Under Stress

Protein hydrolysates are mixtures of peptides and amino acids rather than one uniform active molecule. Reviews report effects on nutrient assimilation, root development and stress-related physiological pathways, including antioxidant and osmotic-response processes. However, source material, hydrolysis process, dose, crop and environment can all change the outcome.

What Biostimulants Cannot Be Claimed to Do

• They are not a substitute for irrigation when the crop lacks water.
• They do not remove salts from saline soil.
• They are not insecticides, fungicides or disease-control products merely because stress tolerance improves.
• They cannot guarantee yield protection under severe or prolonged stress.

How to Judge a Stress-Management Programme in the Field

Define the stress, crop stage and intended outcome first. Compare the exact product programme with the approved recommendation, maintain irrigation/nutrition/crop-protection basics, and judge the response using relevant observations over time rather than one rapid visual change. If performance is weak, use the troubleshooting checklist to separate field, application and product factors.