This review highlights the relationship between the metabolism of reactive oxygen species (ROS), reactive nitrogen species (RNS), and H₂S-reactive sulfur species (RSS). These three metabolic pathways, collectively termed reactive oxygen, nitrogen, and sulfur species (RONSS), constitute a conglomerate of reactions that function as an energy dissipation mechanism, in addition to allowing environmental signals to be transduced into cellular information. This information, in the form of proteins with posttranslational modifications or signaling metabolites derived from RONSS, serves as an inducer of many processes for redoxtasis and metabolic adjustment to the changing environmental conditions to which plants are subjected. Although it is thought that the role of reactive chemical species was originally energy dissipation, during evolution they seem to form a cluster of RONSS that, in addition to dissipating excess excitation potential or reducing potential, also fulfils essential signaling functions that play a vital role in the stress acclimation of plants. Signaling occurs by synthesizing many biomolecules that modify the activity of transcription factors and through modifications in thiol groups of enzymes. The result is a series of adjustments in plants’ gene expression, biochemistry, and physiology. Therefore, we present an overview of the synthesis and functions of the RONSS, considering the importance and implications in agronomic management, particularly on the biostimulation of crops.

The management of water and nutrient ions, such as nitrate, has been studied extensively in recent decades. Increasingly efficient models have been developed for the use of water and nutrients through the automation of fertigation techniques. The application of a fertigation volume for a duration four times longer than applied on the control was evaluated. In Almería (Spain), one pepper crop and two tomato crops—with and without grafting—were grown between Oct. 2013 and June 2014 in a soilless system with a coir substrate. The effects on root growth, plant growth, production, and quality were measured. The following parameters for the fertigation of the nutrient solution and drainage were recorded: % drainage volume, electrical conductivity (EC) of the nutrient solution, pH, and concentration of nitrates and potassium. The absorption of potassium and nitrate, and the nitrate emissions of the drainage were estimated. The results showed an increase in the root volume and an improved distribution in the cultivation unit for the treatment application in the pepper crop. Slowing the applied fertigation improved the absorption of water and nitrates, and the production in the ungrafted tomato and pepper crops, while the grafted tomato crop was unaffected. Nitrate emissions were lower in the evaluated treatment of the pepper and ungrafted tomato crops. The fruit quality parameters were unaffected.

An intercrop is studied here as a new way of farming in soilless systems within a protected environment. To estimate the efficiency of intercropping in this cultivation system, an experiment was conducted to evaluate the effect of the electrical conductivity (EC) of the nutrient solution (2.0, 2.5, and 3.0 dS·m ⁻¹ ) on lettuce and tomato plants and on the agronomic and economic feasibility of the intercrop compared with monoculture. The results indicated that a moderate increase in EC from 2.0 to 3.0 dS·m ⁻¹ did not exert any important effect on tomato plant production or quality but did cause a decrease in lettuce yield in both the first and second crops. Intercropping was only feasible for lettuce when the tomato and lettuce plants were transplanted on the same day. The highest tomato (G class) and lettuce yields were achieved at an EC of 2.5 dS·m ⁻¹ ; this condition resulted in the highest intercrop profitability (0.53 €·m ⁻² more) when compared with tomato monoculture.

In recent decades, salinity in the culture of tomatoes has been one of the most studied parameters. This study aimed to evaluate the effect of a moderate increase in salinity, fertigation distribution, and its control using thermography on a soilless culture of grafted tomato. A tomato crop (cv. Ramyle) grafted onto tomato rootstocks (cv. Emperor) was cultivated in coir crop units at the University of Almeria from Nov. 2012 to May 2013. A plot design subdivided with four blocks was used, with salinity values of 2.0 and 2.5 dS·m ⁻¹ in the main plots and fertigation distribution systems with either one (DD ₁ ) or four (DD ₄ ) drip manifolds in the subplots. The crop productivity was measured using total crop yield, commercial value, and size. The quality parameters in the fruits were not significantly affected. Thermographies were used to aid the control of differential transpiration exerted by salinity. The difference in salinity did not significantly affect the total or commercial production. However, despite being grafted plants, there was a statistically significant effect ( P ≤ 0.05) on the fruit size distribution when the electrical conductivity (EC) of the nutrient solution was increased from 2.0 to 2.5 dS·m ⁻¹ , with a lower production (16%) of large fruits and an increased production of smaller fruits. The DD ₄ system significantly increased large tomato production (22%) compared with DD ₁ , and the quality parameters in the fruits were not significantly affected. As a result of the improvement in tomato size, the DD ₄ distribution system economically offset the required higher initial expenditure compared with the DD ₁ system. Thermography was revealed to be a robust, simple, and quick tool for diagnosing the effect of salinity on transpiration.

Volcanic rock has been used for decades as a horticultural substrate worldwide. In Spain, the use of this material as a substrate is ancient; it was initially used in the Canary Islands because of its volcanic geological origin. At the University of Almería (Almería, Spain), three independent vegetable crops were grown under greenhouse conditions: sweet pepper, tomato, and melon. The volcanic rock came from a location in the geographic center of Spain, which facilitated logistics. Bags of volcanic rock (25 L) were used and were compared with a commercial coconut fiber substrate of an equal volume. All physical, physical–chemical, and chemical parameters of the volcanic rock were determined using European standard analytical procedures. Fertigation was applied, independently adapted to the physical, physical–chemical, and chemical characteristics of each substrate. The cultures were performed under a randomized complete block experimental design. Fertigation parameters, pollutant emissions, fruit production, and the quality of each culture were measured. The results showed that the assessed parameters of the volcanic rock substrate are not a limiting factor for its use as a horticultural substrate. The resultant production and quality were very similar among the three crops compared with a widely used commercial control. Therefore, volcanic rock emerges as a local, sustainable alternative to be used for soilless crop cultivation.

An Acinetobacter calcoaceticus UTMR2 strain was evaluated in tomatillo plants (Physalis ixocarpa Brot.) using a factorial design with different potassium doses (100, 75, 50 and 0% of the recommended dose). In addition to the agronomic parameters, an analysis of the physicochemical, antioxidant, and metabolomic properties of the fruit was performed. The application of the inoculant affected several parameters of the plant (chlorophyll, weight, and contents of several mineral elements) as well as of the fruit (yield, maturity index, FRAP antioxidant capacity, and contents of protein, fiber, and fat). A multivariate analysis was performed by means of a PCA and a heatmap, indicating that the inoculant induced a strong modulating activity in tomatillo plants for the evaluated parameters, with a remarkable effect at low K doses (0 and 50%). The inoculated treatment at 75% of the K dose resulted in similar plant and fruit characteristics to the fully fertilized control. On the other hand, the biofertilized treatment with no K addition resulted in the highest values in the plant and fruit parameters. In addition, from the metabolomics analysis of the fruits at 75% of the K dose, the up-regulation of 4,4″-bis(N-feruloyl)serotonin, salvianolic acid K, and chlorogenic acid was observed, which may have a role in anti-senescence and resistance mechanisms. In conclusion, the rhizobacterial strain had a positive effect on plant growth, nutritional quality, bioactive compounds, and antioxidant activity of tomatillo fruits at reduced doses of K fertilizer, which gives support for its consideration as an effective biofertilizer strain.