Ginés Otálora

We investigated the effect on melon fruits of “fish water” alone or in combination with a supplement of synthetic fertilizers in the nutrient solution or foliar application of Ca(NO₃)₂. These treatments were compared with traditional soilless system with synthetic fertilizers and no re-use of the nutrient solution. The results show that the treatments with recirculation of fish water, and with the foliar supplement, yielded fruits of greater weight and size, but with reduced lightness and lower concentrations of proteins, NO₃^-, K⁺ and total amino acids. The supply of synthetic nutrients to the roots or leaves caused a reduction in the sugar concentrations and the antioxidant activity of these fruits. The use of fish water (alone or with an amendment) increased spermine and putrescine with respect to the traditional soilless crop management. The results for these bioactive compounds in melon should be considered for the maintenance of health with age.

ISHS XXI International Congress on Plastics in Agriculture: Agriculture, Plastics and Environment Photoselective shade nets for pepper cultivation in southeastern Spain

Sweet pepper is among the most widely cultivated horticultural crops in the Mediterranean basin, being frequently grown hydroponically under cover in combination with CO₂ fertilization and water conditions ranging from optimal to suboptimal. The aim of this study is to develop a simple model, based on the analysis of plant stable isotopes in their natural abundance, gas exchange traits and N concentration, to assess sweet pepper growth. Plants were grown in a growth chamber for near 6 weeks. Two [CO₂] (400 and 800 μmol mol⁻¹), three water regimes (control and mild and moderate water stress) and four genotypes were assayed. For each combination of genotype, [CO₂] and water regime five plants were evaluated. Water stress applied caused significant decreases in water potential, net assimilation, stomatal conductance, intercellular to atmospheric [CO₂], and significant increases in water use efficiency, leaf chlorophyll content and carbon isotope composition, while the relative water content, the osmotic potential and the content of anthocyanins did change not under stress compared to control conditions support this statement. Nevertheless, water regime affects plant growth via nitrogen assimilation, which is associated with the transpiration stream, particularly at high [CO₂], while the lower N concentration caused by rising [CO₂] is not associated with stomatal closure. The stable isotope composition of carbon, oxygen, and nitrogen (δ¹³C, δ¹⁸O, and δ¹⁵N) in plant matter are affected not only by water regime but also by rising [CO₂]. Thus, δ¹⁸O increased probably as response to decreases in transpiration, while the increase in δ¹⁵N may reflect not only a lower stomatal conductance but a higher nitrogen demand in leaves or shifts in nitrogen metabolism associated with decreases in photorespiration. The way that δ¹³C explains differences in plant growth across water regimes within a given [CO₂], seems to be mediated through its direct relationship with N accumulation in leaves. The changes in the profile and amount of amino acids caused by water stress and high [CO₂] support this conclusion. However, the results do not support the use of δ¹⁸O as an indicator of the effect of water regime on plant growth.

In many plant species, long-term exposure to elevated CO2 concentration results in a reduction in photosynthetic capacity, known as acclimation. This process is mainly explained by a feedback inhibition mechanism. The supply of a fraction of the nitrogen (N) in the nutrient solution as NH4+ can play an important role in the maintenance of photosynthetic activity and could mitigate the acclimation process. The aims of the present work were to study the photosynthetic response of sweet pepper (Capsicum annuum L.) to CO2 enrichment in Mediterranean greenhouse conditions, throughout the crop growth cycle and to evaluate the supply of NH4+ in the nutrient solution as a strategy to enhance the long-term response to CO2 at different levels of salinity. The experiment was conducted in two identical greenhouses: one with CO2 enrichment according to the ventilation, maintaining a high concentration when the vents were closed and a near-atmospheric level when the vents were open and one without. Sweet pepper plants were grown in both greenhouses, being irrigated with two levels of water salinity and two N sources: (i) NO3– and (ii) NO3– plus NH4+. A reduction in the response of photosynthesis to high CO2 concentration was found in the enriched plants after 135 days of CO2 supply, with respect to the reference plants. The leaf photosynthesis rate measured at high CO2 concentration showed a closer relationship with the leaf N concentration than the non-structural carbohydrate concentration. The relative yield gain of the CO2-enriched plants progressively decreased after reaching a maximum value; this was probably associated with the photosynthetic acclimation process. This decrease was delayed by the use of NH4+ in the nutrient solution at low salinity. Knowledge of the crop phase when acclimation to high CO2 concentration occurs can be the basis for deciding when to impose an early cessation of CO2 application, as a strategy to improve the economic efficiency of CO2 supply in Mediterranean conditions.

We investigated the effect of supplying nitrogen, as NO₃^– or as NO₃^–/NH₄⁺, on the composition of fruits of sweet pepper (Capsicum annuum L. cv. Melchor) plants grown with different CO₂ concentrations ([CO₂]): ambient or elevated (800 μmol mol^–1). The results show that the application of NH₄⁺ and high [CO₂] affected the chroma related to the concentrations of chlorophylls. The concentrations of Ca, Cu, Mg, P, and Zn were significantly reduced in the fruits of plants nourished with NH₄⁺, the loss of Fe being more dramatic at increased [CO₂], which was also the case with the protein concentration. The concentration of total phenolics was increased by NH₄⁺, being unaffected by [CO₂]. Globally, the NH₄⁺ was the main factor that affected fruit free amino acid concentrations. Polyamines were affected differently: putrescine was increased by elevated [CO₂], while the response of cadaverine depended on the form of N supplied.