Francisco Moisés del Amor

This study investigates how nitrogen form (100/0 NO₃⁻ vs. 50/50 NO₃⁻/NH₄⁺), heat stress (43 °C), and foliar proline application interact to modulate the growth, photosynthesis, and nitrogen metabolism of two tomato cultivars (Solanum lycopersicum L.), ‘Cherry’ and ‘Tres Cantos’. Nitrogen-exclusive nutrition optimized biomass accumulation and photosynthetic efficiency. Conversely, mixed nutrition reduced photosynthetic performance but enhanced nitrogen storage and detoxification pathways, as evidenced by a shift in amino acid profiles (decreased glutamate and aspartate alongside increased glutamine and asparagine). Under heat stress, growth declined; however, plants exhibited non-stomatal photosynthetic acclimation. While exogenous proline failed to increase biomass, it significantly enhanced heat tolerance by driving transpiration and evaporative cooling. Cultivar-specific assessments revealed high metabolic plasticity in ‘Cherry’, whereas ‘Tres Cantos’ adopted a conservative strategy centered on the accumulation of protective nitrogenous compounds.

Melatonin is a molecule in plants with antioxidant activity, which plays a role in increasing plant tolerance to biotic and abiotic stresses. We studied the effect of exogenous melatonin (100 µM) application on the physiological and biochemical processes in pepper plants (Capsicum annuum L. cv. Espinosa F1), in combination with three levels of nitrate concentration in the nutrient solution (5, 12 and 30 mM NO₃⁻), and under optimum (26 °C) and heat stress (43 °C) conditions. The results showed that heat stress reduced fresh biomass and photosynthesis in all treatments, especially at 30 mM NO₃⁻, indicating greater heat sensitivity under excess nitrogen. However, melatonin partially mitigated these effects, fully restoring fresh weight at 5 mM NO₃⁻ and increasing net CO₂ assimilation rate (A_CO2) by 15.18% compared with the corresponding heat-stressed group without melatonin. Heat stress increased glucose accumulation by 80.8%, 113.4%, and 74.9% at 5, 12, and 30 mM NO₃⁻, respectively, whereas melatonin reduced this accumulation by 13.25%, 27.29%, and 38.47%. Spermidine increased under heat stress by 106.29%, 476.26%, and 348.96% at 5, 12, and 30 mM NO₃⁻, respectively. Melatonin modulated heat stress responses depending on nitrogen supply, suggesting its potential use to improve pepper tolerance under high-temperature conditions.

Composting seaweed biomass reduces environmental impacts while supporting circular-economy strategies in coastal areas, where seaweed removed for recreational management is commonly treated as waste. This approach aligns with regional and EU policies on circular bioeconomy and coastal ecosystem restoration. This study evaluated the effects of Mar Menor seaweed compost applied at 0%, 15% and 35% on lettuce cultivation. Two nitrogen supply levels (100% and 60%) were also used to assess interactive effects on plant growth and nutrient dynamics. The optimal rate of 15% compost enhanced lettuce growth by 25.1% under 100% N irrigation and by 32.2% under 60% N irrigation, indicating that reduced nitrogen availability did not limit biomass accumulation. Indeed, irrigation nitrogen level did not affect total biomass. Compost addition also improved nutrient content and increased phenolic compounds in leaves. When nitrogen was reduced, the combination with compost further boosted phenolic accumulation, by 39.6% with 15% compost and 34.7% with 35%, suggesting a synergistic response. Overall, seaweed compost improves crop performance and nutritional quality while lowering dependence on synthetic fertilisers. Environmentally and economically, it provides coastal municipalities a sustainable option for managing excess seaweed by converting waste into valuable agricultural inputs and mitigating impacts of algal overgrowth.

The beneficial effects of algae on plant growth are widely known, so the combination of coconut fiber with algae waste from a species such as Caulerpa prolifera, which is an invasive species in the Mar Menor, could become an ideal substrate for leafy vegetable cultivation. The aim of this study was to evaluate the effect of an “algae waste + coconut fiber” combination in different proportions on the cultivation of iceberg lettuce. The proportions studied consisted of 0% algae waste + 100% coconut fiber (0% AW), 50% algae waste + 50% coconut fiber (50% AW), 75% algae waste + 25% coconut fiber (75% AW), and 100% algae waste + 0% coconut fiber (100% AW). Physiological parameters were evaluated. The results obtained showed that the mixture of algae waste and coconut fiber is a great alternative in the production of iceberg lettuce, since the proportion of 50% AW considerably improved the size of the lettuce (54.4%), the total phenol concentration (24.8%), the antioxidant activity (28.2%), the total sugars (14.1%) and reduced its nitrate concentration (24.6%), with respect to the 0% AW plants. These findings support the feasibility of reusing Caulerpa prolifera as a bio-enriched substrate for high-quality lettuce production.

Introduction: The reduced N doses in plant fertilization, combined with the influence of plant growth-promoting bacteria (PGPB), to obtain ecofriendly crops and their derived products can be a significant challenge. Purple cauliflower is an exotic variety that can generate higher profits for farmers and greater interest among consumers seeking novel and healthy foods. Purple cauliflower florets are edible, while the leaves are discarded because they are by-products.Methods: The aim of this research was to investigate the combined effect of PGPB (Azotobacter salinestris strain CECT9690) and three different N doses supplied in the nutrient solution (30%, 60%, and 100%) on plant growth and the quality of florets and by-products. Plant height, total shoot and floret weight, and % dry weight in florets and leaves were improved by A. salinestris inoculation under limited doses of N.Results and discussion: The sugar content in the leaves of plants grown with a limited N dose (30%) and inoculated with PGPB increased by 51% compared to the control. PGPB inoculation increased proteins in the leaves (by 30% with 100% N supply, 33% with 60% N supply, and 16% with 30% N supply). Additionally, PGPB inoculation enhanced potassium (26%) and iron (34%) in leaves of plants under limited N supply. These findings indicate that the combined use of reduced N supply and PGPB inoculation may be considered an ecofriendly strategy to enhance the growth and quality of purple cauliflower, while boosting the valorization of its by-products.

Introduction: The reduction of N supplied combined with the use of biostimulants can be an efficient strategy that allows sustainable agriculture to achieve better economic, nutritional and environmental goals without reducing production. Moreover, the industrial processing of celery generates large amounts of waste. Therefore the purpose of this study was improve crop management strategies to reduce nitrate pollution while turning crop waste into value-added products for others sectors.Methods: Consequently, in this work twelve treatments were examined: three N nitrogen content in the nutrient solution (100% control, 60%, and 30%) combined with the inoculation of the roots with Azotobacter salinestris, and foliar application selenium solution (8 μM, Na₂SeO₄). The celery parts from plants grown under limited N dose showed a higher antioxidant activity and TPC (total phenolic compounds) content.Results and discussion: The antioxidant activity increased 28% in leaves and 41% in by-products and TPC improved 27% in leaves and 191% in by-products respect to the control. Besides, a significant reduction of β-carotene content (56%, 11% and 43% in petioles, leaves and by-products respect to the control, respectively) was obtained in plants fed with restricted dose of N. The catalase activity was not affected by N dose. The inoculation of the plants with Azotobacter, together with a reduced N dose, achieved a greater accumulation of all the parameters studied. This accumulation was maximum when Se was applied to the leaves compared with the control and depending on the celery part: TPC (121-450%); antioxidant activity (60-68%), of catalase activity (59% - 158%), and of pigments content (50-90%). These findings can boost the valorization of celery by-products as excellent source of bioactive compounds.

Due to climate change and exacerbated population growth, the search for new sustainable strategies that allow for greater food productivity and that provide greater nutritional quality has become imperative. One strategy for addressing this problem is the combined use of fertilization with a reduced dose of nitrogen and biostimulants. Celery processing produces a large amount of waste with its concomitant pollution. Therefore, it is necessary to address the valorization of its byproducts. Our results revealed reductions in the biomass, Na, P, Mn, B, sugars, and proteins in the byproducts and increased lipid peroxidation, Fe (all celery parts), and K (byproducts) when the N supplied was reduced. Plants inoculated with Azotobacter salinestris obtained a greater biomass, a higher accumulation of K (byproducts), a build-up of sugars and proteins, reduced concentrations of P, Cu, Mn, B, Fe (petioles), and Zn (byproducts), and reduced lipid peroxidation. The application of Se at 8 μM reinforced the beneficial effect obtained after inoculation with Azotobacter salinestris. In accordance with our results, edible celery parts are recommended as an essential ingredient in the daily diet. Furthermore, the valorization of celery byproducts with health-promoting purposes should be considered.

The use of nitrogen as a fertilizer can be highly risky when used excessively, and it is therefore necessary to find novel techniques to reduce its use. Aquaponics reduces the use of synthetic fertilizers and water, and the leaching of nitrate into the environment. One way to avoid problems due to a reduction in nitrogen availability could be the use of plant growth promoting rhizobacteria (PGPR). This study examines the effect of PGPR on kohlrabi plants grown with a traditional nutrient solution (100S), in combination with “fish water” (50F/50D), or with a supplement of synthetic fertilizers (50F/50D + S). Two formulations were used: T1 (Azospirillum brasilense and Pantoea dispersa) and T2 (Azotobacter salinestris). Irrigation with 50F/50D caused a reduction in several of the measured parameters. The combined application of 50F/50D with T1 attenuated the negative effects. T2 did not present significant effects on the parameters measured. The results obtained with 50F/50D + S hardly showed differences with the 100S. Thus, by irrigating with 50F/50D + S, we were able to maintain the yields while reducing fertilizer use and water. The combined use of T1 and 50F/50D was also positive; however, it would be necessary to continue adjusting the amount of nitrate supplied to maintain production.