Photosynthesis in Organic Tomato with Microalgae: 2026 Guide

Introduction: photosynthesis as the engine of tomato yield

Photosynthesis is the fundamental physiological process that determines crop productivity. In organic tomatoes, optimizing the photosynthetic rate directly translates into greater biomass accumulation, better fruit set, and higher quality fruits. However, factors such as water stress, extreme temperatures, or nutritional deficiencies can limit photosynthetic efficiency, reducing potential yield. In this context, microalgae-based biostimulants emerge as an effective tool to enhance photosynthesis naturally, aligned with the principles of organic agriculture.

Microalgae, especially species like Chlorella vulgaris, contain bioactive compounds such as phytohormones, amino acids, vitamins, and antioxidants that stimulate plant metabolic processes. Their foliar or root application can increase photosynthetic activity, improve nutrient uptake, and enhance tolerance to abiotic stress. This article explores the mechanisms by which microalgae enhance photosynthesis in organic tomato cultivation, offering agronomic data and practical recommendations for their integration into sustainable fertilization programs.

What are microalgae and how do they act as biostimulants?

Microalgae are unicellular photosynthetic organisms that grow in aquatic environments, capable of synthesizing a wide range of bioactive compounds. In agriculture, species such as Chlorella vulgaris and Arthrospira platensis are used as biostimulants due to their richness in phytohormones (auxins, cytokinins, gibberellins), free amino acids, organic acids, polysaccharides, and micronutrients. These compounds act on plant metabolic pathways, modulating processes such as cell division, root elongation, and photosynthesis.

When applied to tomato crops, microalgae stimulate chlorophyll production and the activity of key enzymes in the Calvin cycle, such as Rubisco. Additionally, they promote the synthesis of antioxidant compounds that protect the photosynthetic apparatus from oxidative damage caused by environmental stress. Recent agronomic studies have shown that foliar application of Chlorella vulgaris can increase total chlorophyll content in tomato leaves by up to 20%, improving the quantum efficiency of photosystem II.

Biochemical composition of Chlorella vulgaris relevant to photosynthesis

Chlorella vulgaris contains approximately 50-60% proteins, 10-20% lipids, 10-15% carbohydrates, along with B vitamins, vitamin C, beta-carotenes, and minerals such as iron, zinc, and magnesium. Magnesium is an essential component of the chlorophyll molecule, so its direct supply favors the synthesis of photosynthetic pigments. Likewise, amino acids such as tryptophan and glutamic acid participate in the synthesis of auxins and other growth regulators that promote leaf development and expansion of the photosynthetic area.

Photosynthetic enhancement mechanisms induced by microalgae

Microalgae act on photosynthesis through multiple pathways. First, they increase the concentration of chlorophyll a and b in leaves, improving light capture. Second, they stimulate the activity of the Rubisco enzyme, responsible for CO₂ fixation in the Calvin cycle. Recent research has shown that applying Chlorella extracts can increase Rubisco activity in tomato plants by up to 30% under optimal conditions.

Furthermore, microalgae improve the efficiency of electron transport in photosystem II (PSII), measured as the maximum quantum yield (Fv/Fm). An Fv/Fm value close to 0.83 indicates healthy plants; lower values reflect stress. The application of microalgae has been shown to maintain or even raise Fv/Fm in tomato plants subjected to saline or thermal stress, suggesting a protective effect on the photosynthetic apparatus.

Another relevant mechanism is the induction of antioxidant compound synthesis, such as superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX). These enzymes neutralize reactive oxygen species (ROS) generated under stress, which damage PSII reaction centers. By reducing oxidative stress, microalgae allow photosynthesis to remain active during adverse periods.

Effect on stomatal opening and conductance

Microalgae also influence stomatal regulation. The phytohormones present, such as cytokinins, promote stomatal opening, facilitating gas exchange and CO₂ uptake. This results in a higher net photosynthetic rate. However, under water stress conditions, microalgae help maintain a balance by preventing excessive water loss through the modulation of abscisic acid (ABA). Thus, they improve water use efficiency (WUE) without sacrificing photosynthesis.

Effects on water use efficiency and stress tolerance

Organic tomato cultivation, especially in rainfed or deficit irrigation systems, faces drought episodes that limit photosynthesis. Microalgae improve tolerance to water stress by stimulating root development, increasing the production of compatible osmolytes (such as proline and glycine betaine), and strengthening cell walls. This allows the plant to maintain turgor and photosynthetic activity for longer periods.

Field trials have reported that tomato plants treated with Chlorella vulgaris exhibit greater water use efficiency (up to a 15% increase) compared to untreated plants. Additionally, under saline stress conditions, microalgae reduce sodium accumulation in leaves and increase the K+/Na+ ratio, thereby protecting chloroplasts from ionic damage.

The combination of microalgae with fulvic acids, such as those offered by Ecoganic, further enhances these effects. Fulvic acids improve nutrient absorption and soil microbial activity, creating a favorable environment for root development and photosynthesis. This synergy is especially useful in soils with low organic matter or salinity issues.

Application in organic tomato cultivation: doses and phenological stages

To maximize the benefits on photosynthesis, microalgae application should be carried out at key phenological stages of the tomato. It is recommended to start applications at the seedling stage (2-4 true leaves) to stimulate root development and the formation of healthy leaf area. The second application should coincide with the onset of flowering, when photosynthetic demand is high. A third application during fruit filling helps maintain photosynthetic activity and improve fruit quality.

The recommended dose of microalgae-based biostimulant (such as Chlorella) is 2 to 4 L/ha per application, diluted in enough water to uniformly cover the foliage (200-400 L/ha). Foliar application is the most effective route to stimulate photosynthesis, although it can also be applied to the soil to improve the rhizosphere. It is important to carry out applications during periods of low solar radiation (early morning or at dusk) to avoid degradation of bioactive compounds by UV light.

For a complete organic tomato fertilization program, it is recommended to combine microalgae with organic fertilizers and complementary biostimulants. Ecoganic offers a specific program for organic tomatoes that integrates microalgae, fulvic acids, and micronutrients, designed to optimize photosynthesis and yield.

Compatibility with other organic inputs

Microalgae are compatible with most organic fertilizers and biostimulants. However, they should not be mixed with products containing chlorine or high concentrations of copper, as these can reduce the viability of microalgae cells. It is recommended to perform a compatibility test before mixing on a large scale.

Field results: yield and quality increases

Various field trials have evaluated the impact of microalgae on organic tomato cultivation. In a study conducted in the Murcia region, Spain, foliar application of Chlorella vulgaris (3 L/ha at three stages) increased total yield by 18% compared to the control, with a 12% increase in average fruit weight. Additionally, the treated fruits showed higher soluble solids content (Brix degrees), indicating better organoleptic quality.

In another greenhouse trial, the application of microalgae improved the net photosynthetic rate (measured with an infrared gas analyzer) by 22% during the flowering period. Treated plants also showed greater resistance to powdery mildew incidence, possibly due to the induction of systemic defenses.

These results support the effectiveness of microalgae as biostimulants to enhance photosynthesis and yield in organic tomato cultivation. Available scientific evidence suggests that their regular use can contribute to more sustainable and productive agriculture.

Frequently asked questions about photosynthesis in tomato with microalgae

How do microalgae improve photosynthesis in tomato?

Microalgae provide phytohormones, amino acids, and nutrients that stimulate chlorophyll synthesis, Rubisco enzyme activity, and photosystem II efficiency. They also protect the photosynthetic apparatus from oxidative stress and improve stomatal opening, facilitating CO₂ uptake.

When should I apply microalgae in tomato cultivation?

It is recommended to apply at three key stages: seedling (2-4 leaves), start of flowering, and fruit filling. The typical dose is 2-4 L/ha per foliar application, during low solar radiation hours.

Are microalgae compatible with organic farming?

Yes, microalgae such as Chlorella vulgaris are inputs allowed in organic farming under EU Regulation 2018/848. Ecoganic holds organic certifications that endorse its products.

What results can I expect in tomato yield?

Field trials report yield increases between 15% and 25%, improved fruit weight, and higher soluble solids content. The photosynthetic improvement translates into larger, higher-quality fruits.

Mechanisms of photosynthetic biostimulation in organic tomato using microalgae: efficiency and practical application

The incorporation of microalgae as biostimulants in organic tomato cultivation (Solanum lycopersicum) represents an advanced strategy to optimize photosynthesis without resorting to synthetic fertilizers. Recent research demonstrates that foliar application of Chlorella vulgaris (at a concentration of 10⁶ cells/ml) increases the net photosynthetic rate by 23-28% during the flowering phase, compared to untreated plants. This increase is mainly due to the presence of phytohormones such as cytokinins (up to 4.2 mg/L) and auxins (1.8 mg/L) in the algal extract, which stimulate stomatal densification and the activity of the antenna complex in chloroplasts. Additionally, microalgae provide polyamines (spermidine and putrescine) that protect photosystem II (PSII) from photostress, maintaining the maximum quantum efficiency (Fv/Fm) above 0.78 even under direct solar radiation of 1,200 µmol m⁻² s⁻¹.

A field study conducted in the Almería region (Spain) during the spring-summer cycle of 2023 evaluated the effect of biweekly applications of Scenedesmus obliquus (0.5 g/L) on organic tomato variety 'Raf'. The results showed a significant 31% increase in stomatal conductance (gs), rising from 0.32 to 0.42 mol H₂O m⁻² s⁻¹, which facilitated greater CO₂ uptake and a net assimilation rate of 18.7 µmol CO₂ m⁻² s⁻¹ compared to 14.3 µmol in the control. Concurrently, total chlorophyll concentration (a+b) increased by 19%, reaching 52.3 µg/cm², which improved light absorption capacity in the 400-700 nm range. These improvements translated into a marketable yield of 6.8 kg/m², 22% higher than the control, with a 12% increase in total soluble solids (Brix), indicating greater efficiency in the translocation of photoassimilates to the fruits.

From a practical perspective, it is recommended to apply microalgae in aqueous suspension (optimal concentration of 0.8-1.2 g dry biomass/L) during the early morning hours (between 6:00 and 8:00 a.m.), when stomata are fully open and photosynthetically active radiation (PAR) is below 400 µmol m⁻² s⁻¹. This maximizes the adhesion and penetration of bioactive compounds, reducing evaporation losses. For organic greenhouse tomatoes, a 4-application program is suggested: the first at 15 days post-transplant (to stimulate root and leaf development), the second at the start of flowering (to optimize fruit set), the third during fruit filling (to improve quality), and a fourth at ripening (to maintain photosynthetic activity in senescent leaves). It is crucial to adjust the suspension pH to 6.2-6.5 and add a non-ionic adjuvant (0.05% v/v) to improve foliar coverage, especially on the underside of leaves where stomata are concentrated.

Photosynthetic efficiency data obtained through modulated fluorometry (PAM) reveal that plants treated with microalgae show a 15-18% increase in PSII quantum yield (ΦPSII) and a 22% reduction in non-photochemical quenching (NPQ), indicating that a greater proportion of light energy is directed to photochemistry rather than being lost as heat. Additionally, Rubisco enzyme (ribulose-1,5-bisphosphate carboxylase/oxygenase) activity increases by 27% in microalgae treatments, improving carboxylation and reducing photorespiration under high-temperature conditions (35°C daytime). To implement this technique in organic agriculture, it is recommended to produce algal biomass in low-cost photobioreactors (tubular bag or raceway type) using liquid organic fertilizers (such as fish hydrolysates or compost extracts) as a culture medium, achieving cell densities of 10⁷ cells/ml in 7-10 days.

Related Articles

• Organic Agricultural Biostimulants
• Certified Organic Fertilizers

References

• Sustainable Agroecology — FAO