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Irrigation with desalinated seawater (DSW) is a potential solution for addressing water scarcity in semiarid regions across the globe. However, this strategy may compromise the health of agricultural ecosystems due to the high content of phytotoxic elements (mainly boron, B) in this water. Here, a three-year experiment was carried to evaluate the response of the soil’s physicochemical and microbiological properties, and plant physiology, to three irrigation water treatments (DSW; fresh water, FW; and their blend (1:1), BW) in the presence or not of organic amendments. Lemon trees (Citrus limon (L.) Burm. fil. cv. Eureka), with a higher sensitivity to B toxicity, and apricot trees (Prunus armeniaca L. cv. ‘Búlida’), with a lower one, were used as model plants. Lemon trees irrigated with BW and DSW showed a decline in net photosynthesis and stomatal conductance, and an accumulation of B in leaves that exceeded the toxicity threshold. These effects were stronger in amended soils. In soils cultivated with lemon trees, DSW irrigation increased the water-soluble nitrogen content, the urease activity, and the activity and biomass of the microbial community, and shifted the microbial community structure as compared with the other water treatments. The soil microbial community responses were controlled by the addition of organic amendments. The irrigation of apricots with DSW did not negatively impact plant physiological parameters but increased the soil microbial biomass, as in the case of the lemon tree-soil system. These results suggest that DSW irrigation increases soil microbial biomass in both crop-soil systems but harms the physiological status of the most sensitive crop. Our findings provide an initial approach to evaluate the response of the plant-soil system to DSW.

[SPA] En el área mediterránea está aumentando el uso de mallas de sombreo como protección frente a estreses a/bióticos. El objetivo de este ensayo fue evaluar en limeros la respuesta de índices basados en la temperatura del dosel vegetal (Tc) en diferentes condiciones de riego (estrés y control) y de cultivo (aire libre y sombreo). El ensayo se llevó a cabo en verano-otoño de 2021 en limeros Bearss de 5 años. Junto a medidas del estado hídrico de suelo y planta, se monitorizó de forma continua la temperatura del aire (Ta) y del dosel vegetal (Tc), calculándose varios índices térmicos: Tc-Ta, CWSI. Los resultados mostraron un mejor estado hídrico de los limeros cultivados bajo malla de sombreo, con valores más bajos de Tc, Tc-Ta y CWSI que los cultivados al aire libre. Las condiciones de sombreo permitieron un mejor estado hídrico del cultivo y un menor consumo de agua. [ENG] In the Mediterranean area, the use of shading nets as protection against a-/biotic stresses is increasing. The objective of this trial was to evaluate the response of canopy temperature (Tc) based indices in lime trees under different irrigation (stress and control) and growing conditions (open air and shading). The trial was conducted in summer-autumn 2021 on 5- year-old Bearss lime trees. In addition to measurements of soil and plant water status, air (Ta) and canopy (Tc) temperature were continuously monitored, and several thermal indices were calculated: Tc-Ta, CWSI. The results showed a better water status of lime trees grown under shade netting, with lower values of Tc, Tc-Ta and CWSI than those grown in open-air. The shading conditions allowed a better water status of the crop and a lower water consumption.

The aim of this study was to evaluate the robustness of infra-red thermometry to estimate stomatal conductance (gs) in grapefruit trees. For this purpose, the ability of several thermal indices to determine gs was tested for different: (i) irrigation strategies: full irrigation (FI) and regulated deficit irrigation (RDI), (ii) water sources: transfer water (TW) -optimal for agricultural uses- and saline reclaimed water (RW) and (iii) phenological stages: flowering-sprouting (FS) and fruit growth (FG). During two growing seasons, measurements of gs and canopy temperature (Tc) were taken in 14-year-old ´Star Ruby´ grapefruit trees (Citrus paradisi Macf.,). Air temperature (Ta) was also recorded and then the derived thermal indices: Tc-Ta, and CWSI (crop water stress index) were calculated. Subsequently, thermal-gs correlations were established at different averaged thermal data intervals, and VPD (vapour pressure deficit) and PAR (photosynthetically active radiation) conditions. The results indicated that both, water quality and deficit irrigation, affected negatively gs and Tc during FG. In addition, the highest r2 values in thermal indices-gs correlations were found when i) the thermal data was averaged 60 min before the gs measurement, ii) gs was measured over a wide range of VPD (between 0 and 3.5 kPa), and iii) PAR was 1200 µmol m−2 s−1. The ability of the thermal indices to estimate gs improved under RDI and RW conditions, when compared to the control treatment (TW-FI). Moreover, the thermal indices that more accurately estimated gs were Tc-Ta and CWSI in FS (P < 0.001), and the absolute values of Tc in FG (P < 0.001). Overall, thermal indices obtained by infra-red sensors could be a useful tool to estimate gs in grapefruit trees. However, irrigation treatment, water quality, tree phenological stage and environmental conditions (VPD and PAR) must be considered when interpreting thermal indices-gs correlations

[SPA] Este estudio contribuye al conocimiento de la evapotranspiración de limeros jóvenes en condiciones mediterráneas. La novedad de la metodología propuesta es que la programación del riego se realiza de forma automática en base al contenido volumétrico de agua en el suelo. En este sentido, el objetivo principal de este trabajo fue el de calcular la evapotranspiración del cultivo (ETc) haciendo uso de la ecuación general del balance hídrico. El material vegetal utilizado fueron limeros de dos años de edad (Citrus latifolia Tan. cv. Bearss) cultivados en macetas de 45 L, que fueron equipadas con sensores de capacitancia y matriciales. El riego, el drenaje y el peso de la maceta también fueron registrados continuamente. La programación de riego aseguró un óptimo estado hídrico de las plantas durante el experimento. Los valores de la ETc variaron entre 0,25 y 2,56 L planta-1 día-1 en los meses de invierno y verano respectivamente, con máximos valores en Julio. En conclusión, el peso de la maceta sirvió para validar/determinar la ETc cuando los cambios de biomasa fueron despreciables. Los resultados de este estudio permiten determinar la evapotranspiración de limeros y hacer un manejo del riego desde un enfoque automático. [ENG] This study contributes to the knowledge of evapotranspiration of young lime trees under Mediterranean conditions. The novelty of the proposed methodology is that irrigation scheduling is carried out automatically based on the volumetric water content in the soil. In this sense, the main objective of this work was to calculate crop evapotranspiration (ETc) using the general water balance equation. The plant material used was two-year-old lime trees (Citrus latifolia Tan. cv. Bearss) grown in 45 L pots, which were equipped with capacitance and matrix sensors. Irrigation, drainage, and pot weight were also continuously recorded. The irrigation schedule ensured an optimal water status of the plants during the experiment. ETc values varied between

Ozone has been applied in many processes (drinking water disinfection and wastewater treatment, among others) based on its high degree of effectiveness as a wide-spectrum disinfectant and its potential for the degradation of pollutants and pesticides. Nevertheless, the effects of irrigation with ozonated water on the soil microbial community and plant physiology and productivity at the field scale are largely unknown. Here, we assessed the impact of irrigation with ozonated water on the microbial community of a Mediterranean soil and on Solanum lycopersicum L. agro-physiology and productivity in a greenhouse experiment. For this purpose, we evaluated: i) soil physicochemical properties, soil enzyme activities, and the biomass (through analysis of microbial fatty acids) and diversity (through 16S rRNA gene and ITS2 amplicon sequencing) of the soil microbial community, and ii) the nutrient content, physiology, yield, and fruit quality of tomato plants. Overall, the soil physicochemical properties were slightly affected by the treatments applied, showing some differences between continuous and intermittent irrigation with ozonated water. Only the soil pH was significantly reduced by continuous irrigation with ozonated water at the end of the assay. Biochemical parameters (enzymatic activities) showed no significant differences between the treatments studied. The biomasses of Gram- bacteria and fungi were decreased by intermittent and continuous irrigation with ozonated water, respectively. However, the diversity, structure, and composition of the soil microbial community were not affected by the ozone treatments. Changes in soil properties slightly affected tomato plant physiology but did not affect yield or fruit quality. The stomatal conductance was reduced and the intrinsic water use efficiency was increased by continuous irrigation with ozonated water. Our results suggest that soil health and fertility were not compromised, however ozonated water treatments should

The 70% worldwide surface of olive orchards is irrigated. The evaluation of non-conventional water resources and water-saving techniques has gained importance during the last decades in arid and semiarid environments. This study evaluated the effects of irrigation with two water sources: low-cost water DEsalination and SEnsoR Technology (DESERT) desalinated water (DW) ECw ∼1 dS m−1) and reclaimed water (RW) (ECw ∼ 3 dS m−1) combined with two irrigation strategies: full irrigation (FI) (100% of ETc) and regulated deficit irrigation (RDI, 50% of ETc) on fruit yield, ripening indices, and oil yield and quality of olive trees cv Arbosana planted in Mediterranean conditions. Our results showed that RW without water restrictions increased the fruit yield by 35% due to a slight increase in the fruit weight and, mainly, to a greater fruit set than the control trees; although this did not result in a higher oil yield (g tree−1) since the oil content per fruit dry weight was reduced. The RDI strategy did not decrease the fruit yield despite the fact that olive weight tended to decrease, and it increased the oil yield by ∼14.5%. The combination of both stresses (RW and RDI) neither decreased the fruit yield; however, it significantly reduced oil yield (25% less in 2018) since oil content per fruit dry weight was strongly reduced (40%) compared to control trees. Both RDI treatments, regardless water source, determined acidity levels in olive paste lower than in FI treatments; however, it reduced oil extractability and fatty yield. The finding about oil quality indicated that olive exposure to RW, regardless of the water amount, decreased oil quality mainly due to the reduction of oleic acid and the increase of C18:2/C18:3 ratio and peroxides; on the contrary, both RW and RDI improved the total polyphenols. In all cases, the parameters met the legislation. In short, with appropriate management, RW and RDI have great potential to manage oil olive production; nevertheless, studies

[SPA] El objetivo del trabajo fue evaluar los ritmos diarios de indicadores del estado hídrico de la planta, para la programación del riego de: (I) limeros (Citrus latifolia Tan., cv. Bearss) jóvenes cultivados al aire libre y bajo malla de sombreo, y (II) pomelos (Citrus paradisi Macf., cv. Star Ruby) adultos regados con agua de diferente calidad: agua del trasvase (CE≈1 dS/m) y agua salina regenerada (CE≈3,5 dS/m). Los indicadores mostraron un ritmo circadiano similar en todas las condiciones ensayadas. Los limeros cultivados bajo malla de sombreo presentaron una mayor conductancia estomática y fotosíntesis neta que los cultivados al aire libre. El potencial hídrico de tallo y la temperatura de copa fueron similares en ambas condiciones. Los pomelos regados con agua salina regenerada mostraron valores más bajos de intercambio gaseoso y potencial hídrico de tallo, y una temperatura de copa mayor. En conclusión, las condiciones de sombreo afectaron de forma significativa al intercambio gaseoso, favoreciendo la absorción de CO2. Las plantas regadas con agua regenerada salina mostraron un peor estado hídrico, resultado de que la alta concentración de sales presente en el suelo dificultó la absorción de agua por la planta. [ENG] The main objective of the work was to evaluate the diurnal courses of plant water status indicators for precision irrigation of: (I) young lime trees (Citrus latifolia Tan., cv. Bearss) grown under two growing conditions: open air and shade net, and (II) adult grapefruit trees (Citrus paradisi Macf., cv. Star Ruby) irrigated with two different quality water: Tagus-Segura transfer water (EC≈1 dS/m) and regenerated saline water (EC≈3.5 dS/m). Plant water status indicators showed circadian rhythms in all the studied conditions. Lime plants cultivated under shading net presented higher stomatal conductance and net photosynthesis than plants cultivated in the open air. Slight differences were found in stem water potential and canopy temperature betw

Climate change is one of the main challenges facing the agricultural sector as it strives to meet global food needs. In arid and semiarid areas, the scarcity of water imposes the use of alternative sources - such as reclaimed water (RW) or desalinated water (DW) - and of deficit irrigation strategies, such as regulated deficit irrigation (RDI), in order to maintain productivity. The impact of both alternative water sources and RDI strategies on soil microbial communities in conjunction with the crop response has been little studied, and far less in fruit trees. Here, we evaluated the effects of the irrigation water quantity (RDI or the optimal water amount) and quality (DW or saline RW) on: i) the biomass, composition, and activity of the soil microbial community, and ii) the plant agro-physiological response at the level of the water status, nutrients, vegetative growth, and yield of almond trees. The DW-RDI treatment had a lower vegetative growth than the rest, reducing the nutrient requirements and increasing the contents of organic carbon and nitrogen in soil. This coincided with a significant increase in the bacterial biomass and enzyme activities in soil, as well as with a decrease in plant nutrient use efficiencies and yield. Irrigation with RW increased the fungal biomass. When there were no water restrictions (RW-FI), none of the plant agro-physiological parameters were affected; when RDI was applied (RW-RDI), the highest soil sodicity was reached and vegetative growth and yield were negatively affected, although the plant nutrient use efficiencies did not decrease as much as with DW-RDI. In addition, the plant nutrient use efficiencies were negatively correlated with the soil enzyme activities. These results improve our knowledge of the functioning of plant-soil interactions in Mediterranean crops subjected to different irrigation strategies.

Water shortage and low organic carbon content in soil limit soil fertility and crop productivity. The use of desalinated seawater is increasing as an alternative source of irrigation water. However, it has a high boron (B) content that could cause toxicity in the plant-soil microbial system. Here, we evaluated the responses of the soil microbiota and lemon trees to 3 irrigation B doses (0.3, 1, and 15 mg L) under two types of soil management (conventional, CS; and organic, OS) in a 180-days pot experiment. High B doses promoted B accumulation in soil, reaching harmful concentrations that affected soil biodiversity. Our results suggest a close interaction between B and organic labile fractions that increased B availability in soil solution. Besides, B addition to soil impacted on microbial biomass. The bacterial community showed sensitivity to the B dose. Organic amendment did not increase B soil adsorption but it favored B plant uptake. The highest B dose had a detrimental impact on plant physiology, finally resulting lethal for the plants. Our study provides a comprehensive assessment of the microbes-plant interactions in soils irrigated with water with high B content. This will be fundamental in the design of future fertirrigation strategies.

Pesticides have been used extensively in agriculture to control pests and soil-borne diseases. Most of these pesticides can persist in soil in harmful concentrations due to their intrinsic characteristics and their interactions with soil. Soil solarization has been demonstrated to enhance pesticide degradation under field conditions. Recently, ozonation has been suggested as a feasible method for reducing the pesticide load in agricultural fields. However, the effects of ozonation in the soil microbial community have not been studied so far. Here, we evaluate the combined effects of solarization and ozonation on the microbial community of a Mediterranean soil. For this purpose, soil physico-chemical characteristics and enzyme activities and the biomass (through analysis of microbial fatty acids) and diversity (through 16S rRNA and ITS amplicon sequencing) of soil microbial communities were analyzed in a 50-day greenhouse experiment. The degradation of the pesticides was increased by 20%, 28%, and 33% in solarized soil (S), solarized soil with surface ozonation (SOS), and solarized soil with deep ozonation (SOD), respectively, in comparison to control (untreated) soil. Solarization and its combination with ozonation (SOS and SOD) increased the ammonium content as well as the electrical conductivity, while enzyme activities and soil microbial biomass were negatively affected. Despite the biocidal character of ozone, several microbial populations with demonstrated pesticide-degradation capacity showed increases in their relative abundance. Overall, the combination of solarization plus ozone did not exacerbate the effects of solarization on the soil chemistry and microbial communities, but did improve pesticide degradation.

BACKGROUND Non-conventional water sources and water-saving techniques can be valuable in semi-arid regions, although their long-term effects on citrus quality are little known. This study evaluated the effects of irrigation with two sources, transfer water (TW) and reclaimed water (RW), combined with two irrigation strategies, full irrigation (FI) and regulated deficit irrigation (RDI), on fruit quality of mandarins and grapefruits during eight growth seasons, RESULTS Reclaimed water irrigation in mandarin, without water restriction, influenced maturity index (MI) less than TW-FI, because titratable acidity (TA) increased to a greater degree than soluble solid contents (SSC). Nevertheless, juice quality standards were satisfied. Regardless of the irrigation treatment (FI or RDI), a trend towards increasing fruit weight was also detected with RW. In grapefruit, its rootstock (Citrus macrophylla) enhanced salinity resilience with respect to the rootstock of mandarin (‘Carrizo’ citrange) and, hence, MI was not affected by RW. The RDI strategy, without saline stress (TW-RDI), increased, to a similar degree, both SSC and TA in mandarin fruit, not affecting the MI. In grapefruit, the water stress of RDI did improve the MI due to the TA did not change and SSC increased significantly, the TA did not change. The combination of both strategies, RW-RDI, decreased the MI only in some years because TA increased proportionally more than SSC in mandarin, CONCLUSIONS The medium- and long-term feasibility of using RW and RDI to irrigate citrus was demonstrated. However, they must be performed cautiously and with appropriate management to avoid damaging fruit quality as a result of phytotoxic elements. © 2019 Society of Chemical Industry

[SPA] En España, el desarrollo agrario en general, y citrícola en particular, se encuentra limitado principalmente por la escasez de recursos hídricos. Este panorama de déficit hídrico hace necesaria la búsqueda de soluciones que mejoren la eficiencia en el uso del agua. El objetivo principal de este estudio es la evaluación de la sostenibilidad del riego de precisión en cítricos, con especial atención al uso de recursos hídricos de distinta calidad y de sensores del sistema suelo-planta-atmósfera. El ensayo se llevará a cabo en una parcela de árboles jóvenes de limero (Citrus latifolia Tan., cv. Bearss), en donde se determinarán las necesidades hídricas mediante balance hídrico en macetas-lisímetros y se evaluará el efecto de diversas prácticas (cultivo en meseta y con sombreo) y en otra parcela de árboles adultos de pomelo (Citrus paradisi Macf., cv. Star Ruby) en los que se evaluará la respuesta agronómica y fisiológica al riego deficitario con agua salina procedente de EDAR. Los resultados esperables de este estudio nos permitirán disponer de un conocimiento científico-técnico del riego de precisión en cítricos. [ENG] In Spain, agricultural development in general, and citrus in particular, is limited mainly by the scarcity of water resources. This panorama of water deficit makes it necessary to search for solutions that improve the water use efficiency. The main objective of this study is the evaluation of the sustainability of precision irrigation in citrus trees, with special attention to the use of water resources of different quality and sensors of the soil-plant-atmosphere system. The trial will be carried out on a plot of young lime trees (Citrus latifolia Tan., cv. Bearss), where water needs will be determined by water balance in pots-lysimeters and the effect of various practices (cultivation in ridges and shade screen) will be evaluated and in another plot of adult grapefruit trees (Citrus paradisi Macf., cv. Star Ruby) in which the agronomical and phys

[SPA] La búsqueda de nuevos recursos para el riego es un requerimiento en los agro ecosistemas mediterráneos. Se evaluó el impacto del riego con aguas de distintos suministros sobre la comunidad microbiana del suelo y sobre la fisiología de la planta en cultivos de pomelo y mandarino en el Sureste de España. Se consideraron los siguientes tratamientos: i) Agua procedente del Trasvase Tajo-Segura y de pozo (TW) ii) Agua regenerada procedente de una EDAR de la zona (RW) iii) Riego con TW, excepto en la segunda fase de desarrollo del fruto en la que se regó con RWc iv) Riego con RW, excepto en la segunda fase de desarrollo del fruto en la que se regó con TWc. [ENG] The search for new water resources for irrigation is a mandatory requirement in Mediterranean agroecosystems. The impacts of irrigation with water from different origins were evaluated in the soil microbial community and plant physiology of grapefruit and mandarin trees in the south-east of Spain. The following treatments were considered: i) freshwater from the Tajo-Segura water transfer canal and well (TW) ii) reclaimed water from a wastewater treatment plant ( RW) iii) irrigation with TW, except in the second stage of fruit development when RWc was applied iv) irrigation with RW, except in the second stage of fruit development when TWc was applied. Enzyme activities and phospholipids fatty acids were determined to know the phylum of microbial biomass.

[SPA] Esta tesis doctoral se presenta bajo la modalidad de compendio de publicaciones. La población mundial alcanzará unos 10.000 millones de personas en 2050, según recientes proyecciones (ONU, 2017). Para satisfacer la demanda de alimentos, la agricultura necesitará producir casi el 50% más en 2050 que en 2012. Así pues, el incremento de la productividad agrícola de una manera sostenible, conservando el agua y previniendo la contaminación del suelo debe de ser, actualmente, uno de los principales retos de la investigación agronómica a nivel de ecosistema. Es sabido que el agua es el factor de producción más limitante (CE, 2017), especialmente en áreas semiáridas, como la del Mediterráneo, donde el agua de riego no está siempre disponible debido a su escasez (Pedrero et al., 2015). Al mismo tiempo, las predicciones actuales sobre el cambio climático señalan que en el sur de Europa las olas de calor extremo y la reducción de las precipitaciones y del agua disponible limitarán más aún la productividad agraria dado que se está incrementando la frecuencia e intensidad de los periodos de sequía (García-Galiano et al., 2015; FAO, 2016). El uso de fuentes de agua no convencionales como el agua regenerada (AR) y de estrategias de riego deficitario controlado (RDC) podrían ser alternativas adecuadas para los agricultores. En este sentido, el AR puede ser beneficiosa para los cultivos dado que la presencia de macronutrientes (N, P, K) puede ayudar a reducir los requerimientos de fertilizantes, como el nitrato, dando lugar a importantes ahorros (Pedrero et al., 2013). No obstante, se requiere una gestión adecuada y cuidadosa del N para que sea absorbido por la planta y no se lixivie, contaminando así el suelo y los acuíferos (Laslo et al., 2012). En Murcia, una región agronómica semiárida, el 93% del AR tiene una conductividad eléctrica por encima de 2 dS·m-1 y un 37% por encima de 3 dS·m-1, según datos de ESAMUR. La salinidad está entre los factores ambientales más important, [ENG] This doctoral dissertation has been presented in the form of thesis by publication. World population will reach 10,000 million in 2050 by recent projections (ONU, 2017). To meet the demand for food, agriculture in 2050 will need to produce almost 50% more than in 2012. Thus, the increase of agricultural productivity in a sustainable way, conserving water and preventing soil contamination must be, currently, one of the main challenges of agronomic research at the ecosystem level. It is known that water is the most limiting factor of production (CE, 2017), especially in semi-arid areas, such as the Mediterranean, where irrigation water is not always available due to its scarcity (Pedrero et al., 2015). At the same time, current predictions on climate change indicate that extreme heatwaves and the reduction of rainfall and available water in southern Europe will limit agricultural productivity as the frequency and intensity of drought periods is increasing (García-Galiano et al., 2015, FAO, 2016). The use of unconventional water sources such as reclaimed water (RW) and strategies of regulated deficit irrigation (RDI) could be suitable alternatives for farmers. In this sense, RW can be beneficial for crops since the presence of macronutrients (N, P, K) can help reduce fertilizer requirements, such as nitrate, leading to significant savings (Pedrero et al., 2013). However, an adequate and careful management of the N is required so that it is absorbed by the plant and is not leached contaminating the soil and aquifers (Laslo et al., 2012). In Murcia, a semi-arid agronomic region, 93% of the RW has an electrical conductivity above 2 dS m-1 and 37% above 3 dS · m-1, according to recent data from ESAMUR. Salinity is among the most important environmental factors responsible for substantial losses of production in agriculture worldwide and is one of the serious problems confronting the long-term viability of agriculture in production systems irrigated with RW in semi-ar

[SPA] En las regiones de clima semiárido, el agua es un factor limitante para la producción agrícola y, por tanto, para su desarrollo económico. Además, los escenarios de cambio climático muestran una reducción a medio plazo de los recursos hídricos con un mismo nivel de demanda. Por todo ello es fundamental implementar estrategias de riego dirigidas a paliar, en la medida de lo posible, la escasez de agua y a gestionar de manera más eficiente los escasos recursos disponibles. Por otra parte, la comunidad microbiana del suelo es un componente fundamental del ecosistema y un indicador claro de fertilidad del suelo. En el presente estudio se evalúa la respuesta de la comunidad microbiana del suelo, así como la fisiología y producción vegetal, ante las diferentes estrategias de manejo del agua de riego y el déficit hídrico. [ENG] In semiarid regions, water is a limiting factor for the agricultural production and hence for his economic development. Indeed, climate change scenarios show that water availability will be reduced on the long run, with a similar level of demand. Therefore, it is important to implement alternative irrigation managements in order to palliate water deficit without affecting soil sustainability. Moreover, the soil microbial community is an essential part of the ecosystem and a sensitive indicator of soil fertility. In this study, the responses of soil microbial community, plant physiology and production to alternative water managements and water deficit were evaluated in Mediterranean agroecosystems.

1.Warmer and drier conditions associated with ongoing climate change will increase abiotic stress for plants and mycorrhizal fungi in drylands worldwide, thereby potentially reducing vegetation cover and productivity and increasing the risk of land degradation and desertification. Rhizosphere microbial interactions and feedbacks are critical processes that could either mitigate or aggravate the vulnerability of dryland vegetation to forecasted climate change. 2.We conducted a four-year manipulative study in a semiarid shrubland in the Iberian Peninsula to assess the effects of warming (~2.5°C; W), rainfall reduction (~30%; RR) and their combination (W+RR) on the performance of native shrubs (Helianthemum squamatum) and their associated mycorrhizal fungi. 3.Warming (W and W+RR) decreased the net photosynthetic rates of H. squamatum shrubs by ~31% despite concurrent increases in stomatal conductance (~33%), leading to sharp decreases (~50%) in water use efficiency. Warming also advanced growth phenology, decreased leaf nitrogen and phosphorus contents per unit area, reduced shoot biomass production by ~36% and decreased survival during a dry year in both W and W+RR plants. Plants under RR showed more moderate decreases (~10-20%) in photosynthesis, stomatal conductance and shoot growth. 4.Warming, RR and W+RR altered ectomycorrhizal fungal (EMF) community structure and drastically reduced the relative abundance of EMF sequences obtained by high-throughput sequencing, a response associated with decreases in the leaf nitrogen, phosphorus and dry matter contents of their host plants. In contrast to EMF, the community structure and relative sequence abundances of other non-mycorrhizal fungal guilds were not significantly affected by the climate manipulation treatments. 5.Synthesis: Our findings highlight the vulnerability of both native plants and their symbiotic mycorrhizal fungi to climate warming and drying in semiarid shrublands, and point to the importance of a deeper

Warmer and drier conditions associated with ongoing climate change will increase abiotic stress for plants and mycorrhizal fungi in drylands world‐wide, thereby potentially reducing vegetation cover and productivity and increasing the risk of land degradation and desertification. Rhizosphere–microbial interactions and feedbacks are critical processes that could either mitigate or aggravate the vulnerability of dryland vegetation to forecasted climate change. We conducted a 4‐year manipulative study in a semi‐arid shrubland in the Iberian Peninsula to assess the effects of warming (c. 2.5°C; W), rainfall reduction (c. 30%; RR) and their combination (W+RR) on the performance of native shrubs (Helianthemum squamatum) and their associated mycorrhizal fungi. Warming (W and W+RR) decreased the net photosynthetic rates of H. squamatum shrubs by c. 31% despite concurrent increases in stomatal conductance (c. 33%), leading to sharp decreases (c. 50%) in water use efficiency. Warming also advanced growth phenology, decreased leaf nitrogen and phosphorus contents per unit area, reduced shoot biomass production by c. 36% and decreased survival during a dry year in both W and W+RR plants. Plants under RR showed more moderate decreases (c. 10%–20%) in photosynthesis, stomatal conductance and shoot growth. Warming, RR and W+RR altered ectomycorrhizal fungal (EMF) community structure and drastically reduced the relative abundance of EMF sequences obtained by high‐throughput sequencing, a response associated with decreases in the leaf nitrogen, phosphorus and dry matter contents of their host plants. In contrast to EMF, the community structure and relative sequence abundances of other non‐mycorrhizal fungal guilds were not significantly affected by the climate manipulation treatments. Synthesis. Our findings highlight the vulnerability of both native plants and their symbiotic mycorrhizal fungi to climate warming and drying in semi‐arid shrublands, and point to the importance of a d

The aim of our research was to discover the effects of the long-term irrigation with saline reclaimed (RW) and transfer (TW) water and different irrigation strategies: control (C) and regulated deficit irrigation (RDI) on yield and fruit quality of grapefruit at harvest and during cold storage. T W-RDI treatment decreased tree canopy (TC) and crop load, resulting in a 21% reduction of fruit yield. Regarding fruit quality, RW notably decreased peel thickness at harvest (about 8%); however, this difference was not remained during cold storage. Sugar/acid ratio was mainly increased by RDI, but also by RW, due to an important increase in soluble solid content (11% of average value for TW-RDI, RW-C and RW-RDI). In addition, RDI combined with RW, significantly increased the number of fruits in small category 5 at the end of cold storage. Finally, neither ratio yield/TC nor irrigation water productivity were affected by any irrigation treatments.

The aim of our research was to discover the effects of the long-term irrigation with saline reclaimed (RW) and transfer (TW) water and different irrigation strategies: control (C) and regulated deficit irrigation (RDI) on yield and fruit quality of grapefruit at harvest and during cold storage. TW-RDI treatment decreased tree canopy (TC) and crop load, resulting in a 21% reduction of fruit yield. Regarding fruit quality, RW notably decreased peel thickness at harvest (about 8%); however, this difference was not remained during cold storage. Sugar/acid ratio was mainly increased by RDI, but also by RW, due to an important increase in soluble solid content (11% of average value for TW-RDI, RW-C and RW-RDI). In addition, RDI combined with RW, significantly increased the number of fruits in small category 5 at the end of cold storage. Finally, neither ratio yield/TC nor irrigation water productivity were affected by any irrigation treatments.

Scarce water resources mainly in arid and semi-arid areas have caused an increasing interest for applying irrigation protocols aiming to reduce water spends. The effects of regulated deficit irrigation (RDI) on the performance of apricot trees (Prunus armeniaca L. cv. “Búlida”) were assessed in Murcia (SE Spain), during three consecutive growing seasons (2008-2010). The hypothesis was that RDI would not restrict yield but increase fruit quality while saving water. Two irrigation treatments were established: i) control, irrigated to fully satisfy crop water requirements (100% ETc) and ii) RDI, that reduced the amount of applied water to: a) 40% of ETc at flowering and stage I of fruit growth; b) 60% of ETc during the stage II of fruit growth and c) 50% and 25% of ETc during the late postharvest period (from 60 days after harvest). Stem water potential, gas exchanges, trunk cross-sectional area (TCSA), fruit diameter, yield and fruit quality traits were determined. Vegetative growth was decreased by the use of RDI (12% less TCSA on average for the three years), whereas yield was unaffected. In addition, some qualitative characteristics of the fruits, such as the level of soluble solids, sweetness/acidity relation and fruit colour, were improved by the use of RDI. These results and average water savings of approximately 30%, lead us to conclude that RDI strategies are a possible solution for irrigation management in areas with water shortages, such as arid and semi-arid environments.

Scarce water resources mainly in arid and semi-arid areas have caused an increasing interest for applying irrigation protocols aiming to reduce water spends. The effects of regulated deficit irrigation (RDI) on the performance of apricot trees (Prunus armeniaca L. cv. “Búlida”) were assessed in Murcia (SE Spain), during three consecutive growing seasons (2008-2010). The hypothesis was that RDI would not restrict yield but increase fruit quality while saving water. Two irrigation treatments were established: i) control, irrigated to fully satisfy crop water requirements (100% ETc) and ii) RDI, that reduced the amount of applied water to: a) 40% of ETc at flowering and stage I of fruit growth; b) 60% of ETc during the stage II of fruit growth and c) 50% and 25% of ETc during the late postharvest period (from 60 days after harvest). Stem water potential, gas exchanges, trunk cross-sectional area (TCSA), fruit diameter, yield and fruit quality traits were determined. Vegetative growth was decreased by the use of RDI (12% less TCSA on average for the three years), whereas yield was unaffected. In addition, some qualitative characteristics of the fruits, such as the level of soluble solids, sweetness/acidity relation and fruit colour, were improved by the use of RDI. These results and average water savings of approximately 30%, lead us to conclude that RDI strategies are a possible solution for irrigation management in areas with water shortages, such as arid and semi-arid environments.

[Background and Aims] Water deficit is the most serious environmental factor limiting agricultural production. In this work, the tolerance to water stress (WS) of transgenic plum lines harbouring transgenes encoding cytosolic antioxidant enzymes was studied, with the aim of achieving the durable resistance of commercial plum trees., [Methods] The acclimatization process was successful for two transgenic lines: line C3-1, co-expressing superoxide dismutase (two copies) and ascorbate peroxidase (one copy) transgenes simultaneously; and line J8-1, harbouring four copies of the cytosolic ascorbate peroxidase gene (cytapx). Plant water relations, chlorophyll fluorescence and the levels of antioxidant enzymes were analysed in both lines submitted to moderate (7 d) and severe (15 d) WS conditions. Additionally, in line J8-1, showing the best response in terms of stress tolerance, a proteomic analysis and determination of the relative gene expression of two stress-responsive genes were carried out., [Key Results] Line J8-1 exhibited an enhanced stress tolerance that correlated with better photosynthetic performance and a tighter control of water-use efficiency. Furthermore, this WS tolerance also correlated with a higher enzymatic antioxidant capacity than wild-type (WT) and line C3-1 plum plants. On the other hand, line C3-1 displayed an intermediate phenotype between WT plants and line J8-1 in terms of WS tolerance. Under severe WS, the tolerance displayed by J8-1 plants could be due to an enhanced capacity to cope with drought-induced oxidative stress. Moreover, proteomic analysis revealed differences between WT and J8-1 plants, mainly in terms of the abundance of proteins related to carbohydrate metabolism, photosynthesis, antioxidant defences and protein fate., [Conclusions] The transformation of plum plants with cytapx has a profound effect at the physiological, biochemical, proteomic and genetic levels, enhancing WS tolerance. Although further experiments under field conditions will be required, it is proposed that J8-1 plants would be an interesting Prunus rootstock for coping with climate change.

La gestión del agua constituye un desafío importante en la actualidad, sobre todo en zonas de escasez hídrica. La agricultura es la actividad que más agua consume, y de ahí la necesidad de diseñar estrategias que hagan un uso más eficiente de este recurso. Una de esas estrategias de ahorro de agua es el riego deficitario controlado (RDC), que consiste en reducir los aportes hídricos en ciertas fases del ciclo de cultivo sin alterar los rendimientos de forma considerable. Pero para que estas estrategias sean adoptadas por los agricultores han de ser técnica y económicamente rentables. El objetivo principal de este trabajo es evaluar económicamente el uso de RDC en melocotonero. Para alcanzar el objetivo se han utilizado los datos obtenidos en un experimento de campo en el cual se comparan dos tecnologías de apoyo a la programación del riego (cámara de presión y dendrómetros) y tres tratamientos de RDC. Los tratamientos ensayados con la cámara de presión fueron: RDC (con restricción de riego en la fase II del crecimiento del fruto y periodo post-cosecha), con severo potencial hídrico (T1) que satisfizo el 35% de la ETc, RDC con moderado potencial hídrico (T2) que supuso el 40% de la ETc, y control (T3) que satisface las máximas necesidades del cultivo (115% de la ETc). Con la tecnología de dendrómetros los tratamientos fueron: control (T4) que satisface el 100% de la ETc, RDC (T5) que satisfizo el 55% de la ETc y control (T6) donde se aplica el 115% de la ETc con la intención de calibrar los sensores utilizados en la programación del riego en los tratamientos T4 y T5. La evaluación se ha llevado a cabo mediante un análisis de costes y una evaluación financiera. Los resultados indican que el ahorro de agua en los tratamientos de RDC es hasta del 65% sin mermas significativas de producción o calidad. Además, se han estimado menores costes de producción en los tratamientos RDC, independientemente de la tecnología de apoyo a la programación del riego utilizada. Por ello

The effects of over-expression of two cytosolic antioxidant enzymes (Cu, Zn-SOD and/or APX) on plant nutrition, gas exchange, chlorophyll fluorescence, seed viability and germination in transgenic tobacco (Nicotiana tabacum cv. Xanthi) under deficit irrigation or salinity conditions were investigated. Three transgenic lines of tobacco were used in this study: line 17, harboring 2 copies of the cytosolic CuZn-SOD (cytsod) gene; line 51, with 2 copies of the cytosolic APX (cytapx) gene and line 39, harboring one copy of each gene. Over-expression of cytosolic antioxidants enzymes in tobacco plants resulted in a better growth performance that correlated with an improved photosynthetic capacity and nutrient uptake. Moreover, cytsod or cytapx genes promoted seed germination, and enhanced tolerance to mild water stress. In addition, this enhanced antioxidant capacity protected seeds from ageing during prolonged storage, and stimulated germination under salt stress conditions. These results suggest that cytosolic antioxidant transgenes are useful tools to improve drought tolerance, nutrient uptake and seed germination under stressful conditions.

[SPA] Esta tesis doctoral se presenta por compendio de publicaciones. La escasez de recursos hídricos constituye uno de los principales desafíos del siglo XXI al que se están enfrentando ya numerosas sociedades de todo el mundo. A lo largo del último siglo, el uso del agua aumentó a un ritmo dos veces superior al de la tasa de crecimiento de la población, siendo la agricultura la gran consumidora de agua a nivel mundial, ya que emplea actualmente más del 70% del agua dulce disponible. Por tanto, resulta de vital importancia llevar a cabo estudios encaminados a conseguir una óptima gestión de los recursos hídricos disponibles, especialmente en zonas áridas y semiáridas como el Levante Español, donde se producen la mayor parte de frutas y verduras a nivel nacional, y en la que la pluviometría es especialmente escasa. Además de intentar optimizar la eficiencia en el uso del agua mediante el estudio de nuevas estrategias y sistemas de riego de precisión, otra herramienta útil que debemos tener en cuenta es el uso de modelos de producción agraria. Estos modelos nos permiten simular un gran número de situaciones o escenarios, variando las condiciones de cultivo, la climatología, las prácticas culturales, etc., y permitiendo de este modo predecir la producción y/o calidad de la cosecha en función de nuestros “inputs” de entrada (entre los que se encuentran los aportes hídricos). De este modo es posible estimar previamente (y de forma aproximada) la relación coste-beneficio al final de cada ciclo de cultivo. En esta Tesis Doctoral, defendida el 30 de Octubre de 2014, se han planteado dos objetivos principales, el primero de ellos se centra en evaluar y conocer la calidad del fruto de dos variedades de diferente maduración de melocotonero, en función de distintos regímenes hídricos y carga de cultivo. El segundo objetivo comprende la simulación de la calidad de la cosecha por medio de la parametrización y validación de un modelo mecanístico específico adaptado a las dos vari, [ENG] This doctoral dissertation has been presented in the form of thesis by publication. Water scarcity is one of the main challenges of the XXI century, which is already being faced by many societies all over the world. Throughout the last century, water use grew at twice the rate of population growth. Agriculture is the major consumer of water worldwide and currently employs more than 70% of available freshwater. Therefore it is really important to perform studies leading to optimum management of the available water resources, particularly in arid and semi-arid areas such as the Spanish southeast, where most of the fruit and vegetables are produced at the national level and where rainfall is particularly low. Apart from trying to optimize the water use efficiency through the development of irrigation strategies and the use of precision irrigation systems, another useful tool to bear in mind is the use of physiological and agronomic models. These models allow us to simulate a large number of situations or scenarios, varying growing conditions, climatological conditions, agricultural practices, etc. Thus, these models offer an insight of the production and / or crop quality that will be obtained, taking into account our "inputs" (such as water intake). Thereby it would be possible, to estimate previously (and roughly) the cost-benefit ratio which we will obtain at the end of the growing season. To this end, it is necessary to parameterise and validate each model for each crop and variety under study. This thesis is divided into two main sections; the first one is focused on assessing the fruit quality of two different peach cultivars according to the peach tree architecture (Publications 1 and 3). In the second section it is intended to understand and simulate crop quality through the parameterisation and validation of a specific mechanistic model adapted to the two peach varieties abovementioned (Publications 2 and 4). The two varieties studied were "Flordastar" (

Citrus trees are strongly affected by salinity, especially in countries where irrigation is required as a semi-arid Mediterranean agronomic region. The aims of the study were i) to identify the best reliable plant-based water status indicator for field grown grapefruit trees irrigated with saline reclaimed water during five years of cultivation by measuring seasonal changes in physiological parameters (i.e. gas exchange and stem water potential measurements), leaf structural traits (i.e. leaf chlorophyll content, area-based leaf nitrogen and area-based dry mass), phytotoxic elements and yield; ii) to estimate phytotoxicity thresholds at leaf level. Our results showed that the chlorophyll content was the parameter with the highest number of measures with significant differences (p ≤ 0.05, ANOVA) between trees irrigated with reclaimed water and control trees throughout growing stages. Moreover, Chl a increased linearly with area-based leaf nitrogen (R2 = 0.63; p < 0.001) and area-based dry mass (R2 = 0.64; p < 0.001). We also determined the salt-induced phytotoxicity thresholds at which a reduction in yields occurs; these levels were Na: 0.1 g/100 g, Cl: 0.6 g/100 g and B: 100 ppm. In conclusion, we revealed the importance of leaf chlorophyll measurements as a significance diagnostic indicator of salt stress on field grown grapefruit trees. This parameter was also related to plantbased water status indicators such as stem water potential, stomatal conductance and net photosynthesis. Additionally, a salt accumulation potential at leaf level was shown, leading to possible risk in crop sustainability in the medium to long term.

Citrus trees are strongly affected by salinity, especially in countries where irrigation is required as a semi-arid Mediterranean agronomic region. The aims of the study were i) to identify the best reliable plant-based water status indicator for field grown grapefruit trees irrigated with saline reclaimed water during five years of cultivation by measuring seasonal changes in physiological parameters (i.e. gas exchange and stem water potential measurements), leaf structural traits (i.e. leaf chlorophyll content, area-based leaf nitrogen and area-based dry mass), phytotoxic elements and yield; ii) to estimate phytotoxicity thresholds at leaf level. Our results showed that the chlorophyll content was the parameter with the highest number of measures with significant differences (p . 0.05, ANOVA) between trees irrigated with reclaimed water and control trees throughout growing stages. Moreover, Chl a increased linearly with area-based leaf nitrogen (R2 = 0.63; p < 0.001) and area-based dry mass (R2 = 0.64; p < 0.001). We also determined the salt-induced phytotoxicity thresholds at which a reduction in yields occurs; these levels were Na: 0.1 g/100 g, Cl: 0.6 g/100 g and B: 100 ppm. In conclusion, we revealed the importance of leaf chlorophyll measurements as a significance diagnostic indicator of salt stress on field grown grapefruit trees. This parameter was also related to plantbased water status indicators such as stem water potential, stomatal conductance and net photosynthesis. Additionally, a salt accumulation potential at leaf level was shown, leading to possible risk in crop sustainability in the medium to long term.

This paper deals with the assessment of heterogeneity in water status in a commercial orchard, as a prerequisite for precision irrigation management. Remote sensing-derived indicators could be suitable for mapping water stress over large areas, and recent studies have demonstrated that high resolution airborne thermal imagery enables the assessment of discontinuous canopies as pure tree crowns can be targeted, thus eliminating the background effects. Airborne campaigns were conducted over a drip-irrigated commercial orchard in Southwestern Spain composed of five different orchard tree crops. An unmanned aerial vehicle with a thermal camera onboard was flown three times during the day on 8 July 2010, at 9, 11 and 13 h (local time). Stem water potential was measured at the same time of the flights. In some irrigation units, irrigation was stopped prior to the measurement date to induce water deficits for comparative purposes. Several approaches for using the thermal data were proposed. Daily evolution of the differential between canopy and air temperature (T c - T a) was compared to tree water status. The slope of the evolution of T c - T a with time was well correlated with water status and is proposed as a novel indicator linked with the stomatal behavior. The Crop Water Stress Index (CWSI) was calculated with the temperature data from the 13.00 h flight using an empirical approach for defining the upper and lower limits of T c - T a. The assessment of variability in water status was also performed using differences in relative canopy temperatures. Ample variability was detected among and within irrigation units, demonstrating that the approach proposed was viable for precision irrigation management. The assessment led to the identification of water-stressed areas, and to the definition of threshold CWSI values and associated risks. Such thresholds may be used by growers for irrigation management based on crop developmental stages and economic considerations. © 2013

In order to understand the role of cytosolic antioxidant enzymes in drought stress protection, transgenic tobacco (Nicotiana tabacum cv. Xanthi) plants overexpressing cytosolic Cu/Zn-superoxide dismutase (cytsod) (EC 1.15.1.1) or ascorbate peroxidase (cytapx) (EC 1.11.1.1) alone, or in combination, were produced and tested for tolerance against mild water stress. The results showed that the simultaneous overexpression of Cu/Znsod and apx or at least apx in the cytosol of transgenic tobacco plants alleviates, to some extent, the damage produced by wáter stress conditions. This was correlated with higher water use efficiency and better photosynthetic rates. In general, oxidative stress parameters, such as lipid peroxidation, electrolyte leakage, and H2O2 levels, were higher in non-transformed plants than in transgenic lines, suggesting that, at the least, overexpression of cytapx protects tobacco membranes from water stress. In these conditions, the activity of other antioxidant enzymes was induced in transgenic lines at the subcellular level. Moreover, an increase in the activity of some antioxidant enzymes was also observed in the chloroplast of transgenic plants overexpressing cytsod and/or cytapx. These results suggest the positive influence of cytosolic antioxidant metabolism on the chloroplast and underline the complexity of the regulation network of plant antioxidant defences during drought stress.

Callistemon is an Australian species used as ornamental plant in Mediterranean regions. The objective of this research was to analyse the ability of Callistemon to overcome water deficit in terms of adjusting its physiology and morphology. Potted Callistemon laevis Anon plants were grown in controlled environment and subjected to drought stress by reducing irrigation water by 40% compared to the control (irrigated to container capacity). The drought stress produced the smallest plants throughout the experiment. After three months of drought, the leaf area, number of leaves and root volume decreased, while root/shoot ratio and root density increased. The higher root hydraulic resistance in stressed plants caused decreases in leaf and stem water potentials resulting in lower stomatal conductance and indicating that water flow through the roots is a factor that strongly influences shoot water relations. The water stress affected transpiration (63% reduction compared with the control). The consistent decrease in gs suggested an adaptative efficient stomatal control of transpiration by this species, resulting in a higher intrinsic water use efficiency (Pn/gs) in drought conditions, increasing as the experimental time progressed. This was accompanied by an improvement in water use efficiency of production to maintain the leaf water status. In addition, water stress induced an active osmotic adjustment and led to decreases in leaf tissue elasticity in order to maintain turgor. Therefore, the water deficit produced changes in plant water relations, gas exchange and growth in an adaptation process which could promote the faster establishment of this species in gardens or landscaping projects in Mediterranean conditions.

The use of regulated deficit irrigation (RDI) strategies is becoming a common practice in areas with low water availability. Little information is available about the effects of RDI on the antioxidant content of fruits. In this study, the influence of RDI on the content of vitamin C, phenolic compounds and carotenoids was investigated. Two irrigation strategies, fully irrigated (FI) and RDI, were compared at two levels of thinning, commercial and half of the commercial crop load. RDI strategies affected the content of vitamin C, phenolics and carotenoids of Flordastar peaches. RDI caused fruit peel stress lowering the content of vitamin C and carotenoids, while increasing the phenolic content, mainly anthocyanins and procyanidins. Fruit weight was the only quality index influenced by the crop load as it increased in FI fruits at low crop load. In general, fruits from commercial crop load had slightly higher content of antioxidants to fruits from low crop load, although these influences were only observed in the peel. Additionally, the influence of irrigation controlled by two sensors related to plant water level, maximum daily trunk shrinkage (MDS) and sap flow (SF) on the antioxidant constituents of peaches was evaluated. The response of the fruits to SF sensor was similar to that observed for RDI strategy. According to the tested water sensors, SF did not act as a good plant-based water indicator for use in irrigation scheduling, as it caused an increase in the content of phenolics, similar to that observed for fruits subjected to RDI. Therefore, selection of RDI strategies and plant water indicators should be taken into account as they affect the content of antioxidants of peaches.