The use of biostimulants is becoming a useful tool for increasing crop productivity while enhancing nutritional quality. However, new studies are necessary to confirm that the joint application of different types of biostimulants, together with bioactive compounds, is effective and not harmful to plants. This study examined the impact of applying the biostimulant Green Leaves, comprising Macrocystis algae extract and containing a mixture of amino acids, corn steep liquor extract, calcium, and the bioactive compound glycine betaine. The effect of applying two different doses (3 and 5 mL L⁻¹) of this biostimulant was evaluated on lettuce plants, and growth and quality parameters were analyzed along with photosynthetic efficiency, nutritional status, and nutrient efficiency parameters. The application of Green Leaves improved plant weight (25%) and leaf area and enhanced the photosynthetic rate, the accumulation of soluble sugars and proteins, and the agronomic efficiency of all essential nutrients. The 3 mL L⁻¹ dose improved the nutritional quality of lettuce plants, improving the concentration of phenolic compounds and ascorbate and the antioxidant capacity and reducing NO₃⁻ accumulation. The 5 mL L⁻¹ dose improved the absorption of most nutrients, especially N, which reduced the need for fertilizers, thus reducing costs and environmental impact. In short, the Green Leaves product has been identified as a useful product for obtaining higher yield and better quality.

Salinity stress constitutes one of the main abiotic stresses that considerably reduces crop yield. An approach to enhance plant growth under salt stress involves the addition of humic substances (HS) to roots or leaves. Here, we evaluated the potential use of BLACKJAK®, an HS-based product, to enhance salt tolerance in lettuce (Lactuca sativa L.). For this aim, plants were exposed to salinity (100 mM NaCl), salinity + HS: radicular (R)-HS (0.40 mL/L and 0.60 mL/L) and foliar (F)-HS (7.50 mL/L and 10.00 mL/L), along with a control (without NaCl). Parameters related to plant growth, Na⁺ and K⁺ accumulation, photosynthetic activity, oxidative stress, enzymatic and non-enzymatic antioxidants, as well as proline levels were evaluated. Results showed that R and F-HS considerably enhanced salinity tolerance. In addition, F-HS offered a greater improvement of plant growth in relation to shoot fresh weight, shoot relative growth rate, and foliar area, being 10.00 mL/L the best dose. This tolerance could be associated with reduced Na⁺ translocation to the shoot and enhanced shoot K⁺ accumulation, decreasing Na⁺/K⁺ ratio. Furthermore, HS improved the net photosynthetic rate, Rubisco carboxylation efficiency, and photosystem II performance, and reduced ROS levels and lipid peroxidation. Hence, our data show the potential use of BLACKJAK® to improve lettuce tolerance to salinity, with foliar application slightly better than radicular to achieve this aim, especially at 10.00 mL/L dose.

Alkalinity is an important environmental factor that affects crop production and will be exacerbated in the current climate change scenario. Thus, the presence of carbonates and high pH in soils negatively impacts nutrient assimilation and photosynthesis and causes oxidative stress. A potential strategy to improve tolerance to alkalinity could be the modification of cation exchanger (CAX) activity, given that these transporters are involved in calcium (Ca²⁺) signaling under stresses. In this study, we used three Brassica rapa mutants (BraA.cax1a-4, BraA.cax1a-7, and BraA.cax1a-12) from the parental line 'R-o-18' that were generated by Targeting Induced Local Lesions in Genomes (TILLING) and grown under control and alkaline conditions. The objective was to assess the tolerance of these mutants to alkalinity stress. Biomass, nutrient accumulation, oxidative stress, and photosynthesis parameters were analyzed. ^{The results showed} that BraA.cax1a-7 mutation was negative for alkalinity tolerance because it reduced plant biomass, increased oxidative stress, partially inhibited antioxidant response, and lowered photosynthesis performance. Conversely, the BraA.cax1a-12 mutation increased plant biomass and Ca²⁺ accumulation, reduced oxidative stress, and improved antioxidant response and photosynthesis performance. Hence, this study identifies BraA.cax1a-12 as a useful CAX1 mutation to enhance the tolerance of plants grown under alkaline conditions.

Humic substances (HS) have been defined as a potential plant biostimulant to improve crop yield in a sustainable and environmentally friendly way. Leonardite-suspension concentrate (SC) is a type of HS extracted from lignite that is currently employed to enhance various physiological aspects of plants. However, the different effects between both modes of SC application (root and foliar) are poorly understood, especially on photosynthesis performance. Therefore, this study aimed to investigate the influence of a leonardite-SC-based product (BLACKJAK®), on lettuce growth and photosynthesis efficiency, while comparing both methods of application. For this purpose, four root (R): R1 (0.20 mL/L), R2 (0.40 mL/L), R3 (0.60 mL/L), and R4 (0.80 mL/L), and four foliar: F1 (5.00 mL/L), F2 (7.50 mL/L), F3 (10.00 mL/L), and F4 (12.50 mL/L) BLACKJAK® doses were applied to lettuce plants. Related shoot and root growth parameters, photosynthetic efficiency, and sugar and starch content were assessed in lettuce plants. The results showed that BLACKJAK® improved shoot and root biomass, foliar area, and root length, especially at intermediate doses (R2, R3, F2, and F3), with R3 demonstrating the greatest growth increases. Similarly, the main photosynthetic parameters analyzed (net photosynthetic rate and Rubisco carboxylation efficiency), and the soluble sugars and starch content were improved by the same doses, with R3 showing the best photosynthetic performance. Hence, our study suggests that BLACKJAK® improves lettuce yield and photosynthetic efficiency, particularly with radicular application at R3.

In the present study, we evaluated the potential use of a humic substance (HS)-based biostimulant in mitigating drought stress in lettuce (Lactuca sativa L.) by comparing both root and foliar modes of application. To achieve this, lettuce plants were grown in a growth chamber on a solid substrate composed of vermiculite and perlite (3:1). Plants were exposed to drought conditions (50% of Field Capacity, FC) and 50% FC + HS applied as radicular (‘R’) and foliar (‘F’) at concentrations: R-HS 0.40 and 0.60 mL/L, respectively, and 7.50 and 10.00 mL/L, respectively, along with a control (100% FC). HSs were applied three times at 10-day intervals. Plant growth, nutrient concentration, lipid peroxidation, reactive oxygen species (ROS), and enzymatic and non-enzymatic antioxidants were estimated. Various photosynthetic and chlorophyll fluorescence parameters were also analyzed. The results showed that HS applications alleviated drought stress, increased plant growth, and reduced lipid peroxidation and ROS accumulation. HSs also improved the net photosynthetic rate, carboxylation efficiency, electron transport flux, and water use efficiency. Although foliar HSs showed a greater tendency to enhance shoot growth and photosynthetic capacity, the differences between the application methods were not significant. Hence, in this preliminary work, the HS-based product evaluated in this study demonstrated potential for alleviating drought stress in lettuce plants at the applied doses, regardless of the mode of application. This study highlights HS-based biostimulants as an effective and sustainable tool to improve crop resilience and support sustainable agriculture under climate change. However, further studies under controlled growth chamber conditions are needed to confirm these results before field trials.

Biostimulants are presented as a potential tool to achieve the main objectives of modern agriculture: increase crop yield and nutritional quality while reducing chemical fertilizer use. Here, we investigated the use of a HS-based product (BLACKJAK^®, from Sofbey S.A., Mendrisio, Switzerland) as a biostimulant to enhance plant growth, nitrogen (N), phosphorus (P), and potassium (K) use efficiency, as well as antioxidant capacity. For this purpose, BLACKJAK^® was applied to lettuce (Lactuca sativa L.) as radicular (‘R’) and foliar (‘F’) at doses: 0.20 mL/L (R1), 0.40 mL/L (R2), 0.60 mL/L (R3), and 0.80 mL/L (R4), 5.00 mL/L (F1), 7.50 mL/L (F2), 10.00 mL/L (F3), and 12.50 mL/L (F4), along with a control. Shoot fresh weight (FW) and dry weight (DW), leaf area, NPK use efficiency parameters, and antioxidant capacity were evaluated. Our results showed that R1, R2, R3, F2, and F3 enhanced shoot FW and leaf area, while only R3 increased shoot DW. Furthermore, in general, most of the doses employed enhanced NPK use efficiency parameters such as apparent crop recovery, nutrient export, physiological efficiency, and internal utilization of applied nutrients. Similarly, HS also increased ascorbate, glutathione, and phenol concentrations, showing an improvement in antioxidant capacity measured through FRAP (Ferric Reducing Antioxidant Power) and TEAC (Trolox Equivalent Antioxidant Capacity) assays. Overall, root-HS offered better results than foliar-HS, especially at R3. Hence, our results indicate that BLACKJAK^® could be a good candidate to enhance crop productivity and nutritional quality while reducing the use of chemical NPK fertilizers.