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Trabajo Fin de Master en la Universidad de Sevilla: Escuela Internacional de Posgrado, Chloride (Cl-) has traditionally been considered a harmful element for agriculture due to the assumed toxic effects caused in plants when they accumulate it in large quantities under salinity conditions, and its antagonism with nitrate (NO3-), that can affect the performance of crops. However, Cl- nutrition at macronutrient levels (1-5 mM in nutrient solution) has been proved as a potential strategy to improve growth and development of plants. Among other effects, it has been showed that this beneficial Cl- nutrition reduces between 25-75% the NO3- content in leaves of adult plants, which is potentially harmful to human health. In addition, the exposure of plants to mild salinity levels (also known as eustress) has been tested to modulate plant metabolism system in horticultural crops, inducing the synthesis of beneficial phytochemical components to human diet, reduced levels of NO3- content and possibly prolong post-harvest time and performance. However, it is necessary to determine the right choice of the salt eustress type and dose to induce the synthesis of these protective phytochemicals is crucial to avoid potential interference with plant growth and productivity. Consequently, the study of a potential fertilization with optimal NO3-/ Cl- ratios is relevant to identify the best performance and nutritional quality of young leafy vegetables for human consumption. This tool is key to study and maximize plant growth, increase water content, reduce NO3- accumulation in leaves and improve antioxidant capacity, providing a reduction in the use of nitrogen (N) over-fertilization practices, meaning a more sustainable agriculture for environment and human health. Therefore, this work evidents for the first time the Cl- function at macronutrient and mild salinity levels in the improvement of growth and nutritional quality in lettuce baby-leaves

2 páginas.- 2 referencias.- Poster presentado en el BP2021: XXIV Reunión de la Sociedad Española de Biología de Plantas y XVII Congreso Hispano-Luso de Biología de Plantas, 7 y 8 de julio de 2021. online, Chloride (Clֿ ) is an essential micronutrient that has traditionally been considered a harmful element for plants due to its toxicity and antagonism with nitrate (NOֿ3 ), which represents the major nitrogen source for crops. However, Clֿ application al macronutrient levels exhibits positive effects for plant growth, as a result of improved photosynthetic performance, whole-plant water relations, and water use efficiency l. Furthermore, el nutrition has been shown to improve nitrogen-use efficiency, reducing nitrate accumulation in leaves and, as a result, improving the nutritional quality of agricultural products for human consumption. The agricultural use of NO3̄ in organic and chemical fertilizers is currently a major environmental concern in Europe since excessive NO3̄ concentrations cause water pollution being harmful to people and nature. Therefore, Clֿ arises as a potential strategy to reduce NO3̄ over-fertilization in agriculture by the implementation of new Clֿ / NO3̄ ratios in fertilizers. With this aim, in this work we evaluated whether el- nutrition improves growth and different physiological traits in Tomato plants subjected to increasing NO)' treatments. Tomato plants were grown in semi-hydroponics under greenhouse conditions, and watered with increasing NO3̄ treatments (3-15 mM). In addition, plants from each NO3̄ treatment were subjected to two nutritional treatments: 5 mM Cl--based treatment (CL) and a sulphate+phosphate treatment (SP) as a control, all treatments containing a similar cationic balance. After 30 DAS, tomato plants were harvested and different growth and physiological parameters were analyzed, Our results showed that increasing NO3̄ concentrations induced total, leaf and root growth, remaining with no changes beyond 9 mM NO3̄ . Clֿ -treated plants exhibited stronger growth stimulation in a NO3̄ treatments compared lo SP plants, whereas NO3̄ content was highly reduced. Interestingly, under low NO3̄ (3 mM), el showed similar values of growth, SPAD and water potential to 9 mM NO3̄ without el-, whereas Photosynthesis remained unchanged. In conclusion, our results demonstrated a beneficial effect of Cl' nutrition on tomato plant growth and water status, and more specifically when partially replacing NO3̄ by Clֿ , revealing optimal Clֿ / NO3̄ ratios with high potential to reduce NO3̄ ' fertilization, which could lead to a healthier and sustainable agriculture, Funding for the present research was provided by Ihe Spanish Ministry of Science Innovation and Universities-FEDER grant RTl2018-094460-B-IOO, Spanish National Research Council granl CSIC-202040E266, and European Union's Horizon 2020 research and innovation prograrnme lInder Ihe Marie Sklodowska-Curie granl agreemenl No 895613 .

2 páginas.- 4 referencias.- Poster presentado en el BP2021: XXIV Reunión de la Sociedad Española de Biología de Plantas y XVII Congreso Hispano-Luso de Biología de Plantas, 7 y 8 de julio de 2021. online, Chloride (Cl-) has traditionalIy been considered a damaging ion for agriculture because of its toxicity under salinity conditions and antagonism with nitrate (NO3-). However, Cl- nutrition at macronutrient levels (1-5 mM) has been proved as a potential strategy to improve the performance of different crops·. Mild salinity levels (20-40 mM NaCl) has al so been formulated as a promising way to increase phytochemicals withminimalloss of yield, modulating positively quality of vegetables· Among other effects, the beneficial Cl- nutrition reduces between 25-75% the NO3- content in leaves of adul! tobacco plants, potentialIy harmful to human health . The study of a potential fertilization with optimal N03-/CL- ratios is relevant to identify the best performance and nutritional quality ofyoung lettuce plants, for reducing NO3-, accumulation in leaves and nitrogen overfertilization practices, meaning a more sustainable agriculture for environment and human health. Therefore, in this work we aimed to elucidate the effects of el' supplied at both macronutrient and mild el' salinity levels on physiological parameters, el- and N03- content, ascorbic acid, and different antioxidant capacity tests in lettuce baby-leaves.Lettuce seeds were grown in semi-hydroponics under greenhouse conditions, and treated with four NO3- treatments: 5, 9, 12 and 15 mM of a mix of NO3-, salts. In addition, plants from each NO3- treatment were treated with two er treatments: 5 (5CL) and 25 (25CL) mM of a mix of Cl- salts, and a control treatment with a mix of sulphate+phosphate (SP) salts. Plants were harvested at 15 and 30 days after sowing, and tissues were stored for the analysis anions and antioxidants content.lnterestingly, our results revealed that the 25CL treatment caused the strongest increase of biomass and leaf area at 5 and 9 mM of NO3- levels compared to SP treatments, whereas the los s of water and the N03- contenl was significantly reduced in 25CL and 5CL treatments compared to SP treatments. Antioxidant determinations will be discussed on Ihe pos ter. Therefore, this work demonstrates for the first time the Cl- speeific function of mild Cl- salinity on the improvement of growth and nutritional quality in lettuce baby-leaves., Funding for the present research was provided by the Spanish Ministry of Science [nnovation and Universities-FEDER grant RTI2018-094460-B-100, Spanish Nationa[ Research Council grants CSIC-202040E266 and CS[C-202140E023, and European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska Curie grant agreement No 895613.

Chloride (Cl-) is an anion that participates in key processes for plants, such as photosynthesis and osmotic regulation1. Cl- has recently been defined as a beneficial macronutrient for higher plants, due to the stimulation of plant growth, inducing morphological and cellular changes that include the stimulation of leaf cell size, reducing stomatal conductance and inducing additional osmolarity and turgor in adult tobacco plants. Thus, Cl- generates bigger plants with better water and nitrogen use efficiency and, as a result, a better photosynthetic performance2,3. Roots are in charge of searching for water and nutrients which are essentials for plant development and growth. Nutrients distribute to the rest of plant organs via the vascular system, being regulated by complex hormonal mechanisms4. Although some proteins regulating Cl- homeostasis (e.g. Cation-Chloride Cotransporter) have been reported to be important for root cell elongation5, little is known about the effect of Cl- nutrition on root developmental processes during early vegetative growth. To this aim, in this work tobacco and tomato seeds were sown under greenhouse conditions and seedlings were harvested at different developmental stages, from 8 to 35 days after sowing. A Cl- treatment (5 mM of Cl- salts) was supplemented to the basal nutrient solution, and a treatment with a mix of sulphate+phosphate salts (SP) with the same cationic content was used as a control. Afterwards, biomass and root system architecture (RSA) parameters (primary root length, number and length of lateral roots) were analysed by using `ImageJ¿ and `Optimas¿ software. Results from this work showed that the Cl- treatment generated bigger plants with longer primary roots and shorter lateral roots during the early vegetative development. These effects may be caused by higher cell size or division during the root development, with a possible effect on hormonal regulation. Therefore, these root architecture changes are particularly relevant during early vegetative development, allowing to Cl--fertilized crops with longer roots to reach deeper zones in the soil with more water and nutrients and, consequently, helping to withstand drought periods that are increasingly more frequent because of climate change., Financial support of the Spanish Ministry of science Innovaction and Universities-FEDER grant RTI2018-094460-B-100, European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement Nº 895613 and Spaish National Research Council grants CSIC-202040E266 and CSIC-202140E023; ii)

17 páginas.- 3 figuras.-. 9 tablas.- 63 referencias.- (This article belongs to the Special Issue Application of Chars in Growing Media), The use of peat in traditional cultivation systems and in commercial nurseries is an environmental problem. In this work, we evaluated the partial replacement of peat with different amounts of biochar sourced from vineyard pruning as plant growing substrates. We studied its effect on the growth of lettuce plants under greenhouse and semi-hydroponic conditions. Substrate mixtures contained 30% (v/v) of vermiculite and 70% (v/v) of different biochar:peat treatments as follows: 0:70 (B0), 15:55 (B15), 30:40 (B30), 50:20 (B50), and 70:0 (B70). Higher biochar treatments increased the pH and electrical conductivity of the substrate, negatively affecting plant growth and germination (especially in B70). The partial substitution of peat by 30% biochar (B30) delayed seed germination but improved plant growth and nitrogen use efficiency (NUE), with shoots containing higher levels of organic nitrogen and nitrate. Moreover, it increased the water holding capacity (WHC) and led to an efficient use of nutrients. Our study demonstrates that biochar can successfully replace and reduce peat and N fertilizer consumption. This has the potential to promote more sustainable farming with positive impacts on both plant growth and the environment., This research was funded by European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 895613 and EIT Food program (Black to the Future Project, EIT-21217). This EIT Food activity has received funding from the European Institute of Innovation and Technology (EIT), a body of the European Union, under Horizon Europe, the EU Framework Programme for Research and Innovation. Á.F. García-Rodríguez acknowledges the Spanish National Research Council for providing JAE Intro-ICU grant.