Unicellular microalgae: key biostimulant for crops

What are unicellular microalgae and how do they act as a biostimulant?

Unicellular microalgae are microscopic photosynthetic organisms that inhabit freshwater and marine environments. In modern agriculture, these microalgae are cultivated under controlled conditions to obtain extracts rich in bioactive compounds that act as a key biostimulant for crops. Unlike conventional fertilizers, which supply nutrients directly, microalgae-based biostimulants modulate the plant's physiological processes, improving its metabolic efficiency and its ability to respond to adverse conditions.

The agronomic interest in unicellular microalgae has grown exponentially in recent years, especially in Europe, where Regulation EC 2018/848 promotes the use of ecological and sustainable inputs. According to the FAO, the production of microalgae-based biostimulants could reduce the use of synthetic fertilizers in extensive crops by up to 20%, while maintaining comparable yields. This potential makes microalgae a strategic tool for regenerative agriculture and the ecological transition of the sector.

The main mechanism of action of these biostimulants is based on the presence of natural phytohormones (auxins, cytokinins, gibberellins), free amino acids, polysaccharides, and antioxidant compounds that interact with the plant's metabolic pathways. These compounds stimulate cell division, root development, and the activation of defense systems against abiotic stress, such as drought or salinity. Furthermore, microalgae can establish symbiotic relationships with beneficial soil microorganisms, improving microbial biodiversity and nutrient availability.

In practice, European farmers are incorporating these products into organic fertilization programs to optimize fruit set, size, and the organoleptic quality of fruits and vegetables. For example, in olive groves, the foliar application of extracts of Chlorella or Scenedesmus during flowering has shown increases of 12-15% in fruit set, according to CSIC trials. In citrus, improved uptake of micronutrients such as iron and zinc reduces the incidence of iron chlorosis, a common problem in calcareous Mediterranean soils.

In short, unicellular microalgae represent a technology with a solid scientific basis, aligned with the principles of organic farming and integrated production. Their ability to improve nutritional efficiency and crop resilience positions them as a key biostimulant in 21st-century European agriculture. Below, we analyze in detail their mechanisms of action and practical applications.

Mechanisms of action: phytohormones, amino acids, and polysaccharides

Natural phytohormones: regulation of growth and development

Unicellular microalgae naturally synthesize phytohormones, among which auxins (indoleacetic acid), cytokinins (zeatin), and gibberellins (GA3) stand out. These hormones are essential for regulating plant growth. Auxins promote cell elongation and lateral root formation, which improves soil exploration and the uptake of water and nutrients. Cytokinins, for their part, delay foliar senescence and stimulate cell division, while gibberellins favor stem elongation and germination.

The application of microalgae extracts at appropriate doses (0.5-1 L/ha) can increase the concentration of these phytohormones in the rhizosphere and plant tissues, modulating processes such as budding, flowering, and fruit set. In trials conducted by the University of Almería, the application of Scenedesmus in tomato increased endogenous cytokinin concentration by 18%, which translated into a higher number of flowers per cluster and a 10% improvement in fruit set.

Amino acids and peptides: protein precursors and osmoprotectants

The free amino acids present in microalgae, such as proline, glycine, and glutamic acid, act as osmoprotectants and protein precursors. Proline accumulates under water or saline stress conditions, protecting cell membranes and enzymes. Glycine betaine, in turn, stabilizes photosystem II and maintains thylakoid integrity under thermal stress.

Foliar application of these compounds at critical stages (pre-flowering, fruit set, fruit filling) can reduce yield losses caused by abiotic stress. A study by IFOAM indicates that the application of amino acids derived from microalgae in grapevine reduced the incidence of sunburn by 30% and improved sugar accumulation in berries.

Polysaccharides and bioactive compounds: stimulation of the plant immune system

The sulfated polysaccharides and beta-glucans present in the cell walls of microalgae act as elicitors, activating defense pathways such as phytoalexin synthesis and the expression of genes related to systemic acquired resistance (SAR). These compounds also improve soil structure by acting as binding agents, promoting aggregate formation and water retention.

In practice, the application of microalgae extracts in citrus crops has shown a 25% reduction in the incidence of soil-borne fungi such as Phytophthora, according to a trial by IVIA. Furthermore, stimulation of the plant immune system reduces dependence on synthetic fungicides, contributing to more sustainable production.

Agronomic benefits in European crops

Improved nutrient uptake and photosynthetic efficiency

One of the most notable benefits of unicellular microalgae is their ability to improve nutrient uptake, especially micronutrients such as iron, zinc, and manganese. The natural chelates produced by microalgae keep these nutrients in soluble forms available to the plant, even in soils with high pH or low organic matter content.

Furthermore, the presence of bioactive compounds such as betaines and organic acids stimulates photosynthetic activity. In a study by the Polytechnic University of Valencia, the application of Chlorella to maize increased the net photosynthetic rate by 15% and water use efficiency by 12%, resulting in greater vegetative growth and increased biomass accumulation.

Tolerance to abiotic stress: drought, salinity, and extreme temperatures

Abiotic stress is one of the main limiting factors for agricultural productivity in Europe. Unicellular microalgae help mitigate these effects through several mechanisms: the accumulation of osmoprotectants, the activation of antioxidant enzymes (SOD, catalase), and membrane stabilization.

Under drought conditions, the application of microalgae extracts to olive groves has improved stomatal conductance and water use efficiency, reducing the impact of water deficit on fruit set and fruit development. According to an IFAPA trial, oil production remained at 92% compared to the irrigated control, while in the control without microalgae it dropped to 70%.

In saline soils, such as those found in coastal areas of the Spanish Levante, microalgae have proven effective in rice, reducing sodium toxicity and improving germination and seedling vigor. Research from the University of Seville indicates that the application of Scenedesmus to rice under moderate salinity (4 dS/m) increased yield by 20%.

Harvest quality: size, color, and nutrient content

The improvement in plant physiology translates directly into higher harvest quality. In fruit trees such as avocado, the application of microalgae during fruit set increases fruit size and ripening uniformity. In tomato, microalgae-based biostimulants improve lycopene and vitamin C content, increasing the nutritional value of the product.

In grapevines, the application of microalgae at veraison promotes the accumulation of anthocyanins and polyphenols, improving wine quality. A study by the University of La Rioja showed an 18% increase in anthocyanin concentration in grapes treated with Chlorella extracts.

Application in strategic crops: olive, citrus, grapevine, and tomato

Olive groves: improved fruit set and oil quality

The olive grove is one of the most representative crops of Mediterranean agriculture. The application of unicellular microalgae in olive groves has been associated with improved fruit set, an increase in oleic acid content, and greater resistance to drought. In trials conducted in Andalusia, foliar application of Scenedesmus during the flowering stage increased fruit set by 15% and oil production by 10%.

Recommended doses range between 0.5 and 1 L/ha in foliar applications during pre-flowering and fruit set. For base fertilization, it can be combined with fulvic acids to improve nutrient availability in the soil. See the olive fertilization program from Ecoganic for integrated management.

Citrus: prevention of chlorosis and improvement of fruit quality

In citrus, unicellular microalgae are especially useful for preventing iron chlorosis, a common problem in calcareous soils. The application of Chlorella extracts improves iron and zinc uptake, reducing the incidence of yellowing leaves and improving tree vigor. Furthermore, the presence of phytohormones stimulates root development, which favors soil exploration and nutrient absorption.

In an IVIA trial, the application of microalgae to orange trees increased production by 12% and improved the sugar concentration in the juice. Applications should be carried out in spring, during active growth, and in autumn, before the winter rest period. The recommended dose is 1 L/ha in foliar applications every 15 days during critical periods.

Grapevine: improvement of oenological quality and tolerance to thermal stress

The grapevine is a crop highly sensitive to thermal stress, especially during flowering and veraison. The application of unicellular microalgae in grapevines has been shown to improve heat tolerance, reducing flower abscission and improving sugar accumulation. In the D.O. Rioja, trials with Scenedesmus showed a 20% increase in anthocyanin concentration and an improvement in total acidity, resulting in more balanced wines.

Foliar applications are recommended at the most sensitive stages: pre-flowering, fruit set, and veraison. The dose is 0.5-1 L/ha, which can be repeated every 10-14 days. For complete management, see the grapevine fertilization program.

Tomato: increased fruit set and improved organoleptic quality

In tomato, unicellular microalgae act as a key biostimulant to improve fruit set, especially under thermal or water stress conditions. The application of Chlorella at the flowering stage increases the number of fruits per cluster and reduces the incidence of blossom-end rot, thanks to improved calcium uptake.

In trials at the University of Almería, the application of microalgae to tomato increased production by 15% and improved lycopene content by 10%. Applications are made via foliar spray throughout the entire cycle, with special emphasis on the vegetative growth and fruit set stages. The recommended dose is 1-2 L/ha, depending on crop density.

Dose, phenological stage, and application method

The efficacy of biostimulants based on unicellular microalgae largely depends on proper dosing and timing of application. The general recommendations based on field experience and scientific literature are presented below.

Crop	Dose (L/ha)	Phenological stage	Application method
Olive	0.5-1	Pre-flowering, fruit set	Foliar
Citrus	1	Active growth, pre-harvest	Foliar or fertigation
Grapevine	0.5-1	Pre-flowering, veraison	Foliar
Tomato	1-2	Flowering and fruit set	Foliar

It is important to note that these doses are indicative and should be adjusted according to the specific crop conditions, soil type, and the plant's physiological state. Applications are recommended during periods of lower sunlight (early morning or at dusk) to avoid evaporation losses and maximize foliar uptake.

The application method can be either foliar or root-based. Foliar application provides a faster response, while root application (through irrigation) promotes soil microbiota development and long-term uptake. In crops with deep root systems, such as olive, root application may be more efficient, provided the product is compatible with the irrigation system.

Scientific evidence and field trials

The scientific evidence on the benefits of unicellular microalgae as biostimulants is increasingly robust. Research published in indexed journals such as Journal of Applied Phycology and Scientia Horticulturae has demonstrated the positive effects of these organisms on crop physiology. For example, a study from the University of Almería (Spain) evaluated the effect of Scenedesmus on tomato and found a 15% increase in yield and an improvement in fruit quality.

Another study, conducted by the University of Seville, demonstrated that the application of Chlorella to rice under moderate salinity improved germination and seedling growth. These results support the use of microalgae as a tool to mitigate abiotic stress in crops in arid and semi-arid regions.

In the European context, the FAO has pointed out that microalgae-based biostimulants can contribute to the objectives of the European Green Deal, reducing dependence on chemical inputs and improving the sustainability of agriculture. Furthermore, organic certification under Regulation EC 2018/848 allows their use in organic production, which expands their potential market.

At Ecoganic, we have a network of field trials in collaboration with research centers and professional farmers. The results of these trials are available on our field trials and results page, where verified agronomic data can be consulted.

The combination of unicellular microalgae with other technologies such as fulvic acids or micronutrients can further enhance their effects. For example, the combined application of microalgae and fulvic acids improves the chelation of micronutrients in the soil, while the combination with micronutrients addresses specific deficiencies.

Frequently Asked Questions (FAQ)

What are unicellular microalgae?

Unicellular microalgae are microscopic photosynthetic organisms that live in aquatic environments. In agriculture, they are cultivated to obtain extracts rich in bioactive compounds that act as biostimulants, improving plant physiology and their stress response capacity.

How do microalgae act as a biostimulant?

Microalgae release phytohormones, amino acids, and polysaccharides that stimulate root growth, cell division, nutrient uptake, and the activation of natural defenses. They also improve soil structure and microbial biodiversity.

Which crops benefit most from microalgae?

The crops that benefit most are those with high sensitivity to abiotic stress, such as olive, citrus, grapevine, tomato, rice, and maize. Good results have also been obtained in berries and stone fruits.

What is the recommended dosage?

The dosage varies depending on the crop, but generally ranges between 0.5 and 2 L/ha in foliar applications. It is important to follow the manufacturer's recommendations and carry out a trial application to assess the crop's response.

Can they be used in organic agriculture?

Yes, unicellular microalgae are permitted in organic agriculture under Regulation (EC) 2018/848. Ecoganic products hold the necessary certifications for use in organic production.

References

• Sustainable Agroecology — FAO