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Plant hydraulics is crucial for assessing the plants' capacity to extract and transport water from the soil up to their aerial organs. Along with their capacity to exchange water between plant compartments and regulate evaporation, hydraulic properties determine plant water relations, water status and susceptibility to pathogen attacks. Consequently, any variation in the hydraulic characteristics of plants is likely to significantly impact various mechanisms and processes related to plant growth, survival and production, as well as the risk of biotic attacks and forest fire behaviour. However, the integration of hydraulic traits into disciplines such as plant pathology, entomology, fire ecology or agriculture can be significantly improved. This review examines how plant hydraulics can provide new insights into our understanding of these processes, including modelling processes of vegetation dynamics, illuminating numerous perspectives for assessing the consequences of climate change on forest and agronomic systems, and addressing unanswered questions across multiple areas of knowledge.

Chloride (Cl) is traditionally categorized as an antagonist of nitrate (NO3¿) because Cl¿ hinders plant NO3¿ transport and accumulation. However, we have recently defined Cl¿ as a beneficial macronutrient for higher plants, due to specific functions that lead to more efficient use of water, nitrogen (N) and CO2 under optimal N and water supply. When accumulated in leaves at macronutrient levels, Cl¿ promotes growth through osmotic, physiological, metabolic, anatomical and cellular changes that improve plant performance under optimal NO3¿ nutrition. Nitrate over-fertilization in agriculture can adversely affect crop yield and nature, while its deficiency limits plant growth. To study the relationship between Cl¿ nutrition and NO3¿ availability, we have characterized different physiological responses such as growth and yield, N-use efficiency, water status, photosynthesis, leaf anatomy, pigments and antioxidants in tomato plants treated with or without 5 mM Cl¿ salts and increasing NO3¿ treatments (3¿15 mM). First, we have demonstrated that 5 mM Cl¿ application can reduce the use of NO3¿ in the nutrient solution by up to half without detriment to plant growth and yield in tomato and other horticultural plants. Second, Cl¿ application reduced stress symptoms and improved plant growth under low-NO3¿ conditions. The Cl¿-dependent resistance to low-N stress resulted from: more efficient use of the available NO3¿; improved plant osmotic and water status regulation; improved stomatal conductance and photosynthetic rate; and better antioxidant response. We proposed that beneficial Cl¿ levels increase the crop ability to grow better with lower NO3¿ requirements and withstand N deficiency, promoting a more sustainable and resilient agriculture.

Chloride (Cl−) is traditionally categorized as an antagonist of nitrate (NO3−) because Cl− hinders plant NO3− transport and accumulation. However, we have recently defined Cl− as a beneficial macronutrient for higher plants, due to specific functions that lead to more efficient use of water, nitrogen (N) and CO2 under optimal N and water supply. When accumulated in leaves at macronutrient levels, Cl− promotes growth through osmotic, physiological, metabolic, anatomical and cellular changes that improve plant performance under optimal NO3− nutrition. Nitrate over-fertilization in agriculture can adversely affect crop yield and nature, while its deficiency limits plant growth. To study the relationship between Cl− nutrition and NO3− availability, we have characterized different physiological responses such as growth and yield, N-use efficiency, water status, photosynthesis, leaf anatomy, pigments and antioxidants in tomato plants treated with or without 5 mM Cl− salts and increasing NO3− treatments (3–15 mM). First, we have demonstrated that 5 mM Cl− application can reduce the use of NO3− in the nutrient solution by up to half without detriment to plant growth and yield in tomato and other horticultural plants. Second, Cl− application reduced stress symptoms and improved plant growth under low-NO3− conditions. The Cl−-dependent resistance to low-N stress resulted from: more efficient use of the available NO3−; improved plant osmotic and water status regulation; improved stomatal conductance and photosynthetic rate; and better antioxidant response. We proposed that beneficial Cl− levels increase the crop ability to grow better with lower NO3− requirements and withstand N deficiency, promoting a more sustainable and resilient agriculture.

The differential stomatal regulation of transpiration among plant species in response to water deficit is not fully understood, although several hydraulic traits have been reported to influence it. This knowledge gap is partly due to a lack of direct and concomitant experimental data of transpiration, stomatal conductance and hydraulic traits. We measured sap flux density (Js), stomatal conductance (gs) and different hydraulic traits in five crop species. We aim to contribute to establish the causal relationship between water consumption and its regulation using a hydraulic trait-based approach. The results showed that the species-specific regulation of Js by gs was overall coordinated with the functional hydraulic traits analyzed. Especially relevant was the negative and significant relationship found between the Huber value (Hv) and its functional analogue ratio between maximum Js and gs (Jsmax/gsmax) which can be understood as a compensation to maintain the hydraulic supply to the leaves. Hv was also significantly related to the slope of the relationship between gs and Js response to vapor pressure deficit and explained most of its variability, adding up to evidence recognizing Hv as a major trait in plant water relations. Thus, hydraulic basis for the regulation of tree water use should be considered.

The presence of fruits provokes significant modifications in plant water relations and leaf gas exchange. The underlying processes driving these modifications are still uncertain and likely depend on the water deficit level. Our objective was to explain and track the modification of leaf-water relations by the presence of fruits and water deficit. With this aim, net photosynthesis rate (A(N)), stomatal conductance (g(s)), leaf osmotic potential (psi(pi)), leaf soluble sugars and daily changes in a variable related to leaf turgor (leaf patch pressure) were measured in olive trees with and without fruits at the same time, under well-watered (WW) and water stress (WS) conditions. Leaf gas exchange was increased by the presence of fruits, this effect being observed mainly in WW trees, likely because under severe water stress, the dominant process is the response of the plant to the water stress and the presence of fruits has less impact on the leaf gas exchange. psi(pi) was also higher for WW trees with fruits than for WW trees without fruits. Moreover, leaves from trees without fruits presented higher concentrations of soluble sugars and starch than leaves from trees with fruits for both WW and WS, these differences matching those found in psi(pi). Thus, the sugar accumulation would have had a dual effect because on one hand, it decreased psi(pi), and on the other hand, it would have downregulated A(N), and finally g(s) in WW trees. Interestingly, the modification of psi(pi) by the presence of fruits affected turgor in WW trees, the change in which can be identified with leaf turgor sensors. We conclude that plant water relationships and leaf gas exchange are modified by the presence of fruits through their effect on the export of sugars from leaves to fruits. The possibility of automatically identifying the onset of sugar demand by the fruit through the use of sensors, in addition to the water stress produced by soil water deficit and atmosphere drought, could be of g

There is a controversy regarding when it is appropriate to apply the irrigation restriction in almond trees (Prunus dulcis Mill.) to save water without penalizing yield. We hypothesized that knowing when plants demand fewer photoassimilates would be a good indicator of less sensitivity of the crop to water deficit. One parameter that defines the photosynthetic capacity is the triose phosphate utilization (TPU). Due to its connection to the export of sugars from the leaves to other sink organs, it is a good candidate for being such an indicator. The objective was to analyze the seasonal evolution of the photosynthetic capacity of three almond cultivars (cvs Guara, Marta and Lauranne) subjected to water stress during vegetative, kernel-filling and postharvest stages. Two sustained deficit irrigation (SDI) treatments (SDI75 and SDI65 with water reductions of 25 and 35%, respectively) and a control treatment (FI) consisting of fully irrigated trees were applied. The response of curves A(N)-Ci was analyzed to assess the maximum carboxylation rate (V-cmax), maximum rate of electron transport (J(max)), TPU and mesophyll conductance to CO2. In addition, leaf water potential and yield were measured. Our experimental findings showed any significant differences in the variables analyzed among cultivars and irrigation treatments. However, consistent differences arose when the results were compared among the phenological stages. During the kernel-filling and the postharvest stages, a progressive limitation by TPU was measured, suggesting that the demand for photoassimilates by the plant was reduced. This result was supported by the correlation found between TPU and fruit growth rate. As a consequence, a downregulation in J(max) and V-cmax was also measured. This study confirms that the kernel-filling stage might be a good time to apply a reduction in the irrigation and suggests a method to detect the best moments to apply a regulated deficit irrigation in almond trees.

El estudio se enfocó en la gestión del riego deficitario en plantaciones superintensivas de olivos, utilizando tecnologías avanzadas como vehículos aéreos no tripulados (UAVs) y sensores de turgencia en hoja para obtener datos fisiológicos de la planta. Se examinaron los efectos del estrés hídrico en la producción de frutos y aceite de oliva, así como los aspectos moleculares relacionados con la biosíntesis y calidad del aceite en respuesta a la falta de agua. Los resultados revelaron que el tamaño de la copa de los árboles y la turgencia de los tejidos eran factores críticos para la producción de frutos y aceite de oliva. Se observó que la disminución del riego deficitario afectaba negativamente la producción, con una disminución en el rendimiento del aceite de oliva y la calidad del mismo en árboles con copas de mayor tamaño. Por otro lado, se encontró que el control de la turgencia de las hojas era una herramienta útil para evaluar el estrés hídrico en los olivos y determinar el momento adecuado para la aplicación del riego. Además, se investigaron los aspectos moleculares relacionados con la biosíntesis y calidad del aceite de oliva en respuesta al estrés hídrico. Se descubrió que la expresión de genes involucrados en la biosíntesis del aceite, así como la composición de ácidos grasos, se vieron afectadas por la disponibilidad de agua y la fuente de carbono, lo que podría tener implicaciones en la calidad del aceite producido en condiciones de sequía. La utilización de las nuevas tecnologías como UAVs y sensores instalados en la planta como sensores de turgencia, puede ser una herramienta valiosa para optimizar la cantidad y el momento del riego, lo que a su vez podría mejorar la producción y calidad de frutos y de aceite de oliva. Estos hallazgos destacan la importancia de una gestión eficiente del riego en las plantaciones superintensivas de olivos, especialmente considerando los desafíos actuales de escasez de agua y cambio climático.

The relative contribution of carbon sources generated from leaves and fruits photosynthesis for triacylglycerol biosynthesis in the olive mesocarp and their interaction with water stress was investigated. With this aim, altered carbon source treatments were combined with different irrigation conditions. A higher decrease in mesocarp oil content was observed in fruits under girdled and defoliated shoot treatment compared to darkened fruit conditions, indicating that both leaf and fruit photosynthesis participate in carbon supply for oil biosynthesis being leaves the main source. The carbon supply and water status affected oil synthesis in the mesocarp, regulating the expression of DGAT and PDAT genes and implicating DGAT1-1, DGAT2, PDAT1-1, and PDAT1-2 as the principal genes responsible for triacylglycerol biosynthesis. A major role was indicated for DGAT2 and PDAT1-2 in well-watered conditions. Moreover, polyunsaturated fatty acid content together with FAD2-1, FAD2-2 and FAD7-1 expression levels were augmented in response to modified carbon supply in the olive mesocarp. Furthermore, water stress caused an increase in DGAT1-1, DGAT1-2, PDAT1-1, and FAD2-5 gene transcript levels. Overall, these data indicate that oil content and fatty acid composition in olive fruit mesocarp are regulated by carbon supply and water status, affecting the transcription of key genes in both metabolic pathways.

eaf water potential (psi(leaf)), typically measured using the pressure chamber, is the most important metric of plant water status, providing high theoretical value and information content for multiple applications in quantifying critical physiological processes including drought responses. Pressure chamber measurements of psi(leaf) (psi(leafPC)) are most typical, yet, the practical complexity of the technique and of the underlying theory has led to ambiguous understanding of the conditions to optimize measurements. Consequently, specific techniques and precautions diversified across the global research community, raising questions of reliability and repeatability. Here, we surveyed specific methods of psi(leafPC) from multiple laboratories, and synthesized experiments testing common assumptions and practices in psi(leafPC) for diverse species: (i) the need for equilibration of previously transpiring leaves; (ii) leaf storage before measurement; (iii) the equilibration of psi(leaf) for leaves on bagged branches of a range of dehydration; (iv) the equilibration of psi(leaf) across the lamina for bagged leaves, and the accuracy of measuring leaves with artificially 'elongated petioles'; (v) the need in psi(leaf) measurements for bagging leaves and high humidity within the chamber; (vi) the need to avoid liquid water on leaf surfaces; (vii) the use of 'pulse' pressurization versus gradual pressurization; and (viii) variation among experimenters in psi(leafPC) determination. Based on our findings we provide a best practice protocol to maximise accuracy, and provide recommendations for ongoing species-specific tests of important assumptions in future studies.

The effects of olive waste biochar and green compost as soil amendments on soil physical properties, as well as on physiological parameters and yield of a super-intensive olive crop cultivated under deficit irrigation conditions, were investigated in south-west Spain during the 2021 growing season. Thus, soils were amended with 40 t ha−1 of olive pomace waste biochar, green-compost, or a biochar-compost mixture (50% w/w), and no amended plots were used as control. On a bi-monthly basis, soil pH, water holding capacity, humidity, and resistance to penetrability were determined. In addition, various indicators of the physiological status and water stress of the plant were also monitored. Finally, the olive yield per tree was measured. Results showed that biochar application was the most effective amendment for increasing soil moisture and reducing soil compaction. The latter was evidenced by the significant reduction of the resistance to the penetrability of the amended soils. Plants of the amended plots showed better leaf water potential. In addition, values of the net photosynthesis rate, the average intrinsic water-use efficiency, and the maximum rate of electron transport in the time before the harvest improved significantly in the trees from the biochar-amended plots, for which olive fruit yields increased by about 15% in comparison with the other treatments. Nevertheless, the estimated net oil yield per tree was similar because the olives from the biochar-amended trees contained more moisture. This field trial shows for the first time that by providing the soil with biochar from olive crop waste as an organic amendment, having high water retention capacity, porosity, and stability, it would be possible to reduce the irrigation water needed and maintain plant yields.

El estudio se enfocó en la gestión del riego deficitario en plantaciones superintensivas de olivos, utilizando tecnologías avanzadas como vehículos aéreos no tripulados (UAVs) y sensores de turgencia en hoja para obtener datos fisiológicos de la planta. Se examinaron los efectos del estrés hídrico en la producción de frutos y aceite de oliva, así como los aspectos moleculares relacionados con la biosíntesis y calidad del aceite en respuesta a la falta de agua. Los resultados revelaron que el tamaño de la copa de los árboles y la turgencia de los tejidos eran factores críticos para la producción de frutos y aceite de oliva. Se observó que la disminución del riego deficitario afectaba negativamente la producción, con una disminución en el rendimiento del aceite de oliva y la calidad del mismo en árboles con copas de mayor tamaño. Por otro lado, se encontró que el control de la turgencia de las hojas era una herramienta útil para evaluar el estrés hídrico en los olivos y determinar el momento adecuado para la aplicación del riego. Además, se investigaron los aspectos moleculares relacionados con la biosíntesis y calidad del aceite de oliva en respuesta al estrés hídrico. Se descubrió que la expresión de genes involucrados en la biosíntesis del aceite, así como la composición de ácidos grasos, se vieron afectadas por la disponibilidad de agua y la fuente de carbono, lo que podría tener implicaciones en la calidad del aceite producido en condiciones de sequía. La utilización de las nuevas tecnologías como UAVs y sensores instalados en la planta como sensores de turgencia, puede ser una herramienta valiosa para optimizar la cantidad y el momento del riego, lo que a su vez podría mejorar la producción y calidad de frutos y de aceite de oliva. Estos hallazgos destacan la importancia de una gestión eficiente del riego en las plantaciones superintensivas de olivos, especialmente considerando los desafíos actuales de escasez de agua y cambio climático.

Chloride (Cl–) to typical macronutrient levels to optimize cell elongation and the plant-use efficiency of water, nitrogen and CO2/energy (Colmenero-Flores et al., 2019; Cakmak et al., 2023). Maximal Cl– demand occurs during early vegetative growth, when Cl– limitation determines a strong biomass reduction, a deficiency that could not be compensated by additional NO3– supply. This phenotype was associated with changes in PSII biochemistry, including a reduction of the Electron Transport Rate (ETR). This work aims to determine how Cl– affects chloroplast anatomy and photosynthetic parameters such as ETR, thylakoid proton gradient and non-photochemical quenching (NPQ) during early and late plant growth.

Chloride (Cl-) has been traditionally considered a harmful ion for plants because of its high accumulation in organs and its antagonism with nitrate (NO3-) under salinity conditions.1,2 However, we recently demonstrated the opposite when it gradually accumulated in leaves, defining Cl- as a beneficial macronutrient for plants that improves growth and the efficiency in the use of water, carbon and nitrogen (N).3,4 A major problem for crops is the inefficient application of N fertilizers, causing N deficiency stress in plants and environmental and human health issues5. Therefore, in this work we analysed physiological traits in tomato plants grown under different Cl- and NO3- treatments. . Our results showed that the application of 5 mM Cl- allowed to reduce NO3- supply, maintaining similar plant growth. Overall, Cl- remains as a potential strategy to reduced N deficiency stress symptoms improving growth, turgor maintenance, photosynthesis and antioxidant response in tomato plants.

Irrigation Advisory Services (IAS) are powerful management instruments aiming to achieve the best efficiency in irrigation water use. So far the literature on farmers’ preferences for a specific scheme design of IAS’ characteristics and the related willingness to pay (WTP) is scant. This study provides evidence on farmers’ preference towards six attributes related to the IAS configuration by using a hypothetical choice experiment. Data were collected from an original survey among 108 farmers from Spain, The Netherlands, Italy, Poland and South Africa. Moreover, we investigated the interplay between these preferences and the individual risk attitude (elicited through a lottery task) as a novel contribution. On average, the results suggest a clear farmers’ preference, especially for receiving weather forecasts from the service and for the feature related to water data recording; as the opposite, on average, crop water requirement seems irrelevant. Finally, we found that farmers’ WTP for the different IAS services varies across countries and, in some cases, also according to the individual risk attitude.

In most fruit tree orchards under localised irrigation, only a fraction of the rhizosphere is wetted by irrigation. As this may reduce growth and production, such that there is a demand for information on the optimum number and location of emitters. In a mature ‘Arbequina’ olive orchard with 1667 trees ha-1, we analysed the impact of applying the same amount of water with one vs. two drip irrigation pipes (laterals) per tree row. We had trees under full irrigation, for which irrigation supplies amounted to 80–100% of the crop water needs (ETc), and two deficit irrigation treatments supplying ca. 40% of ETc. We used the HYDRUS 2D/3D (v. 1.11) model to simulate the shape and volume of the fraction of the rhizosphere wetted by irrigation (irrigation bulbs), as well as drainage and soil evaporation. For both full irrigation and deficit irrigation, differences in the soil volume and the soil surface wetted by irrigation were not sufficient to affect drainage and soil evaporation. The greatest values of root length density and root surface per unit volume were found in trees under deficit irrigation with two laterals, and the lowest in fully irrigated trees with one lateral. This, however, was counterbalanced by both the greater size of the irrigation bulbs and the greater soil water contents in the bulbs of the fully irrigated trees, such that water uptake was not enhanced by the second lateral. For 2 consecutive years we found no impact of irrigating with one or two laterals per tree row on water potential and stomatal conductance, shoot and fruit growth, leaf area and production, either for full irrigation or deficit irrigation conditions. Therefore, our findings suggest no benefits of irrigating super high density olive orchards with two laterals instead of one.

New challenges such as climate change and sustainability arise in society influencing not only environmental issues but human's health directly. To face these new challenges IT technologies and their application to environmental intelligent monitoring become into a powerful tool to set new policies and blueprints to contribute to social good. In the new H2020 project, WatchPlant will provide new tools for environmental intelligence monitoring by the use of plants as "well-being"sensors of the environment they inhabit. This will be possible by equipping plants with a net of communicated wireless self-powered sensors, coupled with artificial intelligence (AI) to become plants into "biohybrid organisms"to test exposure-effects links between plant and the environment. It will become plants into a new tool to be aware of the environment status in a very early stage towards in-situ monitoring. Additionally, the system is devoted to be sustainable and energy-efficient thanks to the use of clean energy sources such as solar cells and a enzymatic biofuel cell (BFC) together with its self-deployment, self-awareness, adaptation, artificial evolution and the AI capabilities. In this concept paper, WatchPlant will envision how to face this challenge by joining interdisciplinary efforts to access the plant sap for energy harvesting and sensing purposes and become plants into "biohybrid organisms"to benefit social good in terms of environmental monitoring in urban scenarios. © 2021 Owner/Author.

Despite the importance of understanding plant growth, the mechanisms underlying how plant and fruit growth declines during drought remain poorly understood. Specifically, it remains unresolved whether carbon or water factors are responsible for limiting growth as drought progresses. We examine questions regarding the relative importance of water and carbon to fruit growth depending on the water deficit level and the fruit growth stage by measuring fruit diameter, leaf photosynthesis, and a proxy of cell turgor in olive (Olea europaea). Flow cytometry was also applied to determine the fruit cell division stage. We found that photosynthesis and turgor were related to fruit growth; specifically, the relative importance of photosynthesis was higher during periods of more intense cell division, while turgor had higher relative importance in periods where cell division comes close to ceasing and fruit growth is dependent mainly on cell expansion. This pattern was found regardless of the water deficit level, although turgor and growth ceased at more similar values of leaf water potential than photosynthesis. Cell division occurred even when fruit growth seemed to stop under water deficit conditions, which likely helped fruits to grow disproportionately when trees were hydrated again, compensating for periods with low turgor. As a result, the final fruit size was not severely penalized. We conclude that carbon and water processes are able to explain fruit growth, with importance placed on the combination of cell division and expansion. However, the major limitation to growth is turgor, which adds evidence to the sink limitation hypothesis.

The effects of olive waste biochar and green compost as soil amendments on soil physical properties, as well as on physiological parameters and yield of a super-intensive olive crop cultivated under deficit irrigation conditions, were investigated in south-west Spain during the 2021 growing season. Thus, soils were amended with 40 t ha−1 of olive pomace waste biochar, green-compost, or a biochar-compost mixture (50% w/w), and no amended plots were used as control. On a bi-monthly basis, soil pH, water holding capacity, humidity, and resistance to penetrability were determined. In addition, various indicators of the physiological status and water stress of the plant were also monitored. Finally, the olive yield per tree was measured. Results showed that biochar application was the most effective amendment for increasing soil moisture and reducing soil compaction. The latter was evidenced by the significant reduction of the resistance to the penetrability of the amended soils. Plants of the amended plots showed better leaf water potential. In addition, values of the net photosynthesis rate, the average intrinsic water-use efficiency, and the maximum rate of electron transport in the time before the harvest improved significantly in the trees from the biochar-amended plots, for which olive fruit yields increased by about 15% in comparison with the other treatments. Nevertheless, the estimated net oil yield per tree was similar because the olives from the biochar-amended trees contained more moisture. This field trial shows for the first time that by providing the soil with biochar from olive crop waste as an organic amendment, having high water retention capacity, porosity, and stability, it would be possible to reduce the irrigation water needed and maintain plant yields.

Biochar is the solid by-product of the pyrolysis of residual biomass. Numerous authors have previously demonstrated that biochar addition to soils improves soil physical properties and plant growth (De la Rosa et al., 2014; Campos et al., 2020, 2021). Additionally, the production of biochar has taken attention during the last decade as a way to valorise abundant residual biomasses, such as waste from the olive oil agro-industry. Another important issue is the need for irrigation in super-intensive olive plantations, which are mainly located in the Mediterranean region, with a semi-arid climate. In this work, the application of biochar to the soil is proposed to increase water retention, improve soil permeability, and at the same time valorise a waste product such as the residual olive pomace. Green compost was also used to compare biochar with the traditional amendment. Soils at a super-intensive plantation of arbequina olive trees under deficit irrigation (“La Hampa” field station, Coria del Río, Seville, Spain) were amended with 40 t ha-1 of biochar, green-compost or a 50% w/w biochar-compost mixture. Un-amended plots were used as control. The field experiment lasted 380 days. Soil properties (pH, electrical conductivity, water holding capacity), soil humidity and resistance to penetrability at field, physiological status of olive trees [midday stomatal conductance (gs), net photosynthesis rate (AN) and maximum rate of electron transport (ETRmax)] were determined on a monthly basis. At harvest (October 2021) the productivity in olives and oil per tree was determined. All the organic amendments showed high porosity and water retention capacity. Biochar application resulted the most effective in reducing soil compaction and improving the water status of olive trees in this super-intensive olive trees plantation. Moreover, the use of biochar increased about 15% olive yields, although net olive production was maintained, Campos P., Miller A.Z., Prats S.A., Knicker H., Hagemann N. & De la Rosa J.M. (2020) - Biochar amendment increases bacterial diversity and vegetation cover in trace element-polluted soils: A long-term field experiment. Soil Biol.Biochem., 150, 1080141. Campos P., Knicker H., López R. & De la Rosa J.M. (2021) - Application of Biochar Produced from Crop Residues on Trace Elements Contaminated Soils: Effects on Soil Properties, Enzymatic Activities and Brassica rapa Growth. Agronomy, 11, 1394. De la Rosa J.M., Paneque M., Miller A.Z. & Knicker H. (2014) - Relating physical and chemical properties of four different biochars and their application rate to biomass production of Lolium perenne on a Calcic Cambisol during a pot experiment of 79 days. Sci. Tot. Environ., 499, 175-184.

Editorial on the Research Topic Proceedings of Olivebioteq 2018 – Olive Management, Biotechnology and Authenticity of Olive Products OLIVEBIOTEQ'18 was the 6th International Conference on the Olive Tree and Olive Products. Held in Seville, Spain, in October 2018, it gathered 218 registered participants from 16 countries with the objective of bringing together the latest advances and knowledge in the areas of breeding and propagation; reproductive and molecular biology, genomics, and biotechnology; crop response to biotic and abiotic stresses and crop management; economics of the olive crop and olive products; table olive and olive oil quality, authenticity, technology, and by-products; and nutrition and health. For all these areas, we considered research, technological, industrial, and commercial aspects.

Increasing the efficiency of on-farm water use requires wise decisions on the irrigation system, the irrigation strategy and the method to schedule irrigation, among other factors related to water management. Since the early 2000s, the water productivity approach has been widely used to address this issue. It provides useful indicators to both the biophysical water productivity and the economic performance of irrigation. Analysis of the literature, however, shows both confusion on the use of terms and lack of agreement on the equations. We have addressed the rational use of the water productivity approach for the irrigator to improve both biophysical and economic water productivity at the field scale. We also addressed the increasing use of the water footprint approach at the field scale. The literature shows a lack of consensus on the reliability of the conceptual framework behind that approach. We focused on its potential for irrigation decision making, and concluded that it is not advantageous, as compared to the water productivity approach, for assessing on-farm water use. In addition, we show a case study of a super high density olive orchard which analyses the joint use of economic water productivity indicators and both production and profit functions to improve decision making.

Chloride (Cl−) has been recently described as a beneficial macronutrient, playing specific roles in promoting plant growth and water-use efficiency (WUE). However, it is still unclear how Cl− could be beneficial, especially in comparison with nitrate (NO3−), an essential source of nitrogen that shares with Cl− similar physical and osmotic properties, as well as common transport mechanisms. In tobacco plants, macronutrient levels of Cl− specifically reduce stomatal conductance (gs) without a concomitant reduction in the net photosynthesis rate (AN). As stomata-mediated water loss through transpiration is inherent in the need of C3 plants to capture CO2, simultaneous increase in photosynthesis and WUE is of great relevance to achieve a sustainable increase in C3 crop productivity. Our results showed that Cl−-mediated stimulation of larger leaf cells leads to a reduction in stomatal density, which in turn reduces gs and water consumption. Conversely, Cl− improves mesophyll diffusion conductance to CO2 (gm) and photosynthetic performance due to a higher surface area of chloroplasts exposed to the intercellular airspace of mesophyll cells, possibly as a consequence of the stimulation of chloroplast biogenesis. A key finding of this study is the simultaneous improvement of AN and WUE due to macronutrient Cl− nutrition. This work identifies relevant and specific functions in which Cl− participates as a beneficial macronutrient for higher plants, uncovering a sustainable approach to improve crop yield. © 2019 The Authors The Plant Journal © 2019 John Wiley & Sons Ltd

Effective study and management of crops and forests would benefit greatly from useful plant-based indicators of the biological controls on evapotranspiration, and particularly stomatal conductance (g s ). Given the strong influence of g s on bulk leaf water potential and turgor pressure (P), in vivo measurement of P may provide useful information about diurnal or seasonal dynamics of g s . Moderate plant water stress affects the diurnal dynamics of P as leaf-to-air vapour pressure deficit (D) varies, and these dynamics correlate to g s . Here, we explored relative changes in P in response to changes in D under mild drought conditions, and how these changes are linked to stomatal behaviour, and specifically to diurnal maximum g s (g s,max ), one of the best indicators of plant water stress. We monitored ecophysiological and environmental variables, as well as a relative proxy for P, during three consecutive seasons in a hedgerow olive orchard where trees were supplied with different irrigation treatments to create well-watered and moderately water-stressed conditions. Our results demonstrated that the sensitivity of P to D correlated well with g s,max reached by the trees within a range in which variations in g s are the main diffusional limitation to photosynthesis. We further showed that this correlation held under a wide range of meteorological conditions and soil water availability. This turgor proxy measurement, which is much easier to measure than g s , can facilitate the use of g s,max as an indicator of plant water stress and evapotranspiration in agriculture and plant science research. © 2019 The Authors

The hydraulic traits of plants, or the efficiency of water transport throughout the plant hydraulic system, could help to anticipate the impact of climate change and improve crop productivity. However, the mechanisms explaining the role of hydraulic traits on plant photosynthesis and thus, plant growth and yield, are just beginning to emerge. We conducted an experiment to identify differences in growth patterns at leaf, root and whole plant level among four wild olive genotypes and to determine whether hydraulic traits may help to explain such differences through their effect on photosynthesis. We estimated the relative growth rate (RGR), and its components, leaf gas exchange and hydraulic traits both at the leaf and whole-plant level in the olive genotypes over a full year. Photosynthetic capacity parameters were also measured. We observed different responses to water stress in the RGRs of the genotypes studied being best explained by changes in the net CO2 assimilation rate (NAR). Further, net photosynthesis, closely related to NAR, was mainly determined by hydraulic traits, both at leaf and whole-plant levels. This was mediated through the effects of hydraulic traits on stomatal conductance. We observed a decrease in leaf area: sapwood area and leaf area: root area ratios in water-stressed plants, which was more evident in the olive genotype Olea europaea subsp. guanchica (GUA8), whose RGR was less affected by water deficit than the other olive genotypes. In addition, at the leaf level, GUA8 water-stressed plants presented a better photosynthetic capacity due to a higher mesophyll conductance to CO2 and a higher foliar N. We conclude that hydraulic allometry adjustments of whole plant and leaf physiological response were well coordinated, buffering the water stress experienced by GUA8 plants. In turn, this explained their higher relative growth rates compared to the rest of the genotypes under water-stress conditions.

NASA's Mars 2020 (M2020) rover mission includes a suite of sensors to monitor current environmental conditions near the surface of Mars and to constrain bulk aerosol properties from changes in atmospheric radiation at the surface. The Mars Environmental Dynamics Analyzer (MEDA) consists of a set of meteorological sensors including wind sensor, a barometer, a relative humidity sensor, a set of 5 thermocouples to measure atmospheric temperature at ∼1.5 m and ∼0.5 m above the surface, a set of thermopiles to characterize the thermal IR brightness temperatures of the surface and the lower atmosphere. MEDA adds a radiation and dust sensor to monitor the optical atmospheric properties that can be used to infer bulk aerosol physical properties such as particle size distribution, non-sphericity, and concentration. The MEDA package and its scientific purpose are described in this document as well as how it responded to the calibration tests and how it helps prepare for the human exploration of Mars. A comparison is also presented to previous environmental monitoring payloads landed on Mars on the Viking, Pathfinder, Phoenix, MSL, and InSight spacecraft.

Successful growth, both vegetative and reproductive, are the final goals for plants. In the case of erops, knowing how plants make use of the available resourees to convert them into biomass, and espeeially, what is the main limiting factor for growth, is of paramount importanee. Although much effort has been dedieated to study how different agronomieal practices affect crop water relations and leaf gas exchange, we still lack the knowledge on the precise conditions that favour or limit plant growth. The classieal view, shared among most seientists, is that earbon limit plant growth. This coneeption makes sense sinee photoassimilates are the brieks to build the biomass. However, other proeesses are as important as C02 uptake. In particular, the maintenance of turgor is as critical for growing as photosynthesis. This misconception on the key limiting factor for growth, giving a major role to the souree aetivity instead of the sink aetivity, has emerged from the limitation and availability ofteehnical methods to evaluate both. In our researeh group we have developed novel methods to overcome these limitations, and we have made them suitable for their use under fieId conditions and long period of time during the growing season. Our results confirrn some opinions found in the literature and support, now with empirical evidence, that photosynlhesis, in most cases, is not lhe main limiting factor for growth but turgor. The new coneept "hours of turgor" emerges and will help us understand the perfonnanee of a speeies under a given environment and the funetional physiological traits thal make the difference in growth among species.

Water seareity is one of the main restrietions to aehieve food security for a growing population. Thus, new defieit irrigation strategies are being developed based on plant physiology but surprisingly, little is known on fruit physiology. The reeent results on the importanee on non-struetural earbohydrates (NSC) to faeilitate osmotie adjustment (Blum, 2017) and their differential transport depending on the water stress level (Gersony et al., 2020) eould be useful to explain the effeet of fruil loading on plant water relations but it has not been studied yet. The aim of this work is to study the effeet of the fruit presenee or absenee on the leaves water relations mediated by their effeet on leaf soluble sugar dynamies and thus, on leaf osmotie potential analyzing (i) the regulation of stomatal eonduetanee (gs), net photosynthesis (AN) and leafwater potential ('I'lcar) produeed by fruits and (ii) determine leaf osmotie potential (lt) and NSC dynamies depending on the presenee or absenee of fruits and water stress. The experiment was earried out between July and November 2018 on twelve olive trees. Six of them were well-watered (WW) trees and the rest were water-stressed (WS). In eaeh of these treatments, half had the presenee of fruits (+) and the other half had absenee of fruils (-) (n = 3). AN, gs, 'l'le,r, were measured weekly and lt and NSC eontent were measured in four speeifie moments in eaeh tree. The results showed that WW+ presented higher AN and gs values, lower leaf NSC and lt less negative than WW-, indieating that earbohydrates were being exported to the fruit. Assuming that fruits behave as a earbon sink organ, we also observe that WS+ presented more negative 'l'le,r values than WS-. This response would be modulated by the hydrie treatments, beeause the effeet of AN and gs was not as prominent in WS nor that of the hydrie potential in WW. In eonclusion, our results suggested that fruits can modulate leaf NSC and maintain the earbon and water relations u