Understanding and Combating Crop Stress

Technical articles - Productivity

Field crops Field crops Water stress Nutrients Biostimulants Deficiencies Biotic stressors Thermal stress

Diagram of different types of stress that can affect crops

Like all living beings, plants are subject to various stresses that can compromise their growth, reproduction, or even survival. Whether biotic or abiotic in origin, these stresses trigger a series of complex responses in plants. Understanding the different types of stress, the defense mechanisms they deploy, as well as the essential role of nutrients in their resilience, is today a challenge for sustainable agriculture.

Different types of stress

Thermal stress

High temperatures cause physiological and metabolic damage. At low temperatures, plant growth slows down considerably. In case of frost, ice crystals can form in the tissues, causing cellular damage and sometimes plant death.

Water stress

Water stress is one of the most common. It causes an imbalance between evapotranspiration and water absorption, which prevents the plant from efficiently transporting nutrients from the root to the leaves. This stress has consequences on the growth and production of crops and can lead to plant death.

Moreover, excess water in the environment causes a lack of oxygen because water displaces air from the soil.

Stress related to lack or excess of light

Light is the energy source for photosynthesis. Each plant variety has its own light and sun requirements. A lack or excess influences plant growth and development. Excess light, especially in case of strong UV radiation, can cause leaf burns.

Stress due to absence or excess of nutrients

Nutrient deficiency affects plant growth, but excess nutrients also have negative effects, such as excess nitrogen which can hormonally constrain the plant from reaching maturity.

Salt stress

This stress can occur due to excess salt in the soil or in irrigation water. It causes a difference in osmotic pressure between the soil and the plant roots, which limits water absorption and thus creates water stress, ionic stress, and nutritional stress.

Mechanical stress

This stress is caused by disturbances generated by the use of agricultural machinery and tools used in agricultural activities, such as pruning or thinning, as well as those caused by weather conditions like hail or wind.

Stress caused by biotic stressors

Plants can suffer attacks from biotic stressors that limit or affect their development. Furthermore, the application of treatments to combat them can also be stressful, depending on the conditions under which the treatment is carried out.

Anthropic stress

Anthropic activities (activities carried out by human populations) are also a source of stress because they cause pollution, mechanical stress or can even lead to excess water due to over-irrigation.

Response mechanisms

Stress perception and regulation

The plant response mechanism to abiotic stress is multi-level and multi-process. It first involves stress detection, then transduction, transcription and signal processing, translation, and finally protein modification. It is a complex response mechanism involving multiple genes, signaling pathways, and metabolic processes.

Plants detect environmental changes via sensors located in different cellular parts (cell wall, plasma membrane, cytoplasm, etc.). These sensors activate secondary messengers (such as calcium ions Ca²⁺, protein kinases, etc.) that trigger a cascade of molecular responses. Specific proteins then regulate the expression of stress tolerance genes, leading to modifications that allow plants to adapt. For example, drought and salinity cause osmotic stress that forces plants to accumulate solutes like proline or soluble sugars to retain water.

Implications for agriculture

• Current research aims to identify genes involved in stress tolerance to improve agricultural yields despite unfavorable conditions.
• However, a major challenge remains balancing growth and resistance: under stress, plants often reduce their growth to conserve resources.
• Approaches such as genetic engineering or varietal selection seek to maximize productivity while increasing resilience.

Role of nutrients in combating stress

Generally, under stress conditions, plants' nutrient requirements increase. Needs decrease only if the stress source is an excess of a nutrient.

For example, potassium increases plant resistance to abiotic stresses because it has several roles such as regulating water retention and controlling stomatal opening and closing, which increases drought tolerance by reducing water loss. In potato cultivation, it can also help fight against frost.

Another example is calcium, an essential element for the growth of new cell tissues and which helps rigidify the cell wall. It thus promotes the mechanical resistance of plants to stress. Studies on potato crops have also shown that foliar applications of calcium, allowing rapid increase of available amounts, help more effectively combat stresses such as heat and frost.

For a detailed overview of the role of macronutrients and micronutrients, see the article: Managing deficiencies in field crops

Observing and measuring stress in plants

To effectively combat stress in plants, it is necessary to diagnose which stress the plant is suffering from.

Visual observations

In case of nutrient deficiencies, leaf observations can be made to determine which nutrient the plant lacks.

pH-Redox approach

The redox potential is an indicator of stress in plants, as redox reactions regulate plant mechanisms. Thus, a good pH/Redox balance is necessary for plant health.

Sap analyses

Sap analyses allow identification of deficiencies and excesses during the crop cycle.

Nutriscope

Measurement with the Nutriscope on rapeseed

The Nutriscope is a scanner developed by Senseen that provides real-time information on plant stress and health. This device uses spectrometry and artificial intelligence to quantify parameters related to plant health (chlorophyll, nutrients…) and help farmers precisely manage their fertilization by identifying deficiencies, excesses, or imbalances.

Chlorophyll fluorescence

Measuring chlorophyll fluorescence allows detection of a range of stresses disrupting the photosynthetic activity of plants. It reveals the presence of stress, can identify its cause, and can also predict symptom onset (from 2 to 25 days depending on deficiencies) and measure the corrective effect of fertilizer applications. Seven types of mineral stress (N, K, Ca, Mg, Fe, Mn, B) can be identified using this method.

A stress source disrupts photosynthesis and thus electron transfer mechanisms, which can be detected by fluorimetry.

How to combat abiotic stresses?

Nutrient supply

Thus, depending on the type of stress the plant is experiencing, supplying certain nutrients can help the plant fight, for example with potassium supply in case of thermal stress.

Biostimulants

To combat abiotic stresses, the application of biostimulants can also help the crop.

Biostimulants contribute to the development and growth of plants and can help them resist abiotic stresses. Biostimulant products strengthen plant vigor and thus stress tolerance.

Biostimulants can be applied by spraying on crops, on seeds, or directly into the soil. The use of biostimulants promotes nutrient absorption and thus plant development.