A striking incongruity has long persisted in the modeling framework typically used to predict CO2 and water vapor exchange between land plants and the atmosphere across scales. Generally, photosynthetic CO2 demand is estimated using process-based models of biochemistry, but the biophysical stomatal constraint on photosynthesis and transpiration (gsw) is estimated using "black box" empirical or optimization-based models. Empirical models of gsw can only be parameterized in the domain of the training data, limiting confidence in predictions made outside that domain; optimization-based models rely on eco-evolutionary "goal functions" about which there remains poor consensus. To resolve this incongruity, we present a novel process-based model for gsw with parameters that all have biophysical meaning, and of which only two require empirical fitting, thus ensuring tractability for application in land-surface models (LSMs). The model successfully reproduces variation in gsw diurnally, globally, and in relation to soil drought and when drought and heat co-occur. The model also has greater functionality than previous models, by predicting stomatal closure under soil drought, the effect of variations in soil-leaf hydraulic conductance, stomatal closure in response to soil and atmospheric drought in darkness, and stomatal opening at high temperatures in both low and high light. With structure and parameters based on physiological processes, this model can translate continuing improvement in understanding of underlying biophysical and molecular genetic causes into predictions for carbon and water exchange, offering greater confidence for predicting the influence of stomata on land-surface exchanges of mass and energy in future climates.

Plant sap analysis typically relies on destructive sampling and immediate freezing, limiting field deployment and longitudinal studies. We introduce a minimally invasive microfluidic device that extracts sap from the stem of Solanum lycopersicum and dries it in situ, enabling storage analogous to dried blood spots in humans. Using both artificial phytohormone mixtures and tomato sap, we assessed the stability of dried samples stored at room temperature for up to seven days and observed no substantial degradation of key phytohormones. Device performance was further validated in a paired sampling experiment, showing strong agreement with a conventional stem severing method for tZR and ABA quantification. These findings demonstrate that dried sap sampling via a microfluidic device provides a practical, field ready alternative to destructive methods, supporting repeated sampling from the same plant and enabling longitudinal metabolic monitoring.

Angiosperms rose to ecological dominance through innovations that enhanced photosynthetic capacity and water-use efficiency. We propose that a pivotal, yet underappreciated, contributor was the hydroactive stomatal mechanism, an abscisic acid-mediated, metabolically driven control of guard-cell turgor. Unlike passive hydraulic responses to changes in water status, hydroactive regulation enables rapid, multisignal integration and minute-scale adjustment of stomatal aperture, synchronising carbon gain with hydraulic safety under fluctuating light, CO2, and evaporative demand. We argue that this water-status control module complemented other stomatal signalling pathways responsive to light, CO2, and metabolism, improving physiological coordination in dynamic environments. This perspective reframes stomata as decision-making nodes linking leaf anatomical evolution, physiological plasticity, and angiosperm diversification and offers a foundation for engineering climate-resilient crops under climate change.

Chloride (Cl-), long regarded as a micronutrient or salinity-associated ion, is now recognized as a beneficial macronutrient in higher plants. This study evaluated whether Cl- supplied at macronutrient concentrations enhances drought resistance in tomato (Solanum lycopersicum L.) through improved physiological performance and nutrient efficiency. Tomato plants were grown under greenhouse conditions under well-watered (CTR) or water-deficit (WD) regimes, receiving either micronutrient (SP) or macronutrient (CL) Cl- supply. At macronutrient levels, Cl- alleviated drought-induced growth inhibition, maintaining both vegetative and reproductive biomass and promoting adaptive root growth. CL-treated plants exhibited enhanced leaf water status, reduced stomatal conductance (gs) without compromising net photosynthesis rate (AN), and increased intrinsic water use efficiency (WUEᵢ) during WD. Cl- also preserved PSII efficiency, maintained chlorophyll levels, reduced lipid peroxidation (MDA), and enhanced total antioxidant capacity. Nutritionally, Cl- improved nitrogen and cation (K+, Ca2+, and Mg2+) utilization efficiencies under drought conditions. Principal component analysis integrating physiological and nutritional traits under WD revealed that CL plants maintained a coordinated and functionally integrated response associated with improved water status, photosynthetic efficiency, and nutrient use. Overall, these findings indicate that Cl- acts as a true macronutrient enhancing drought resilience in tomato through coordinated effects on osmotic adjustment, nutrient optimization, and oxidative stress mitigation. Incorporating Cl- into fertilization programs may therefore represent a cost-effective and sustainable strategy to improve crop WUE and productivity under water-limited conditions.

Despite being an essential micronutrient and its recent classification as a beneficial macronutrient, chloride (Cl-) has traditionally been considered of limited agricultural relevance and a potentially toxic saline ion. This study provides the first comprehensive demonstration of the quantitative and qualitative importance of Cl- during early vegetative development (EVD) of tobacco and Arabidopsis thaliana plants. During this developmental stage, these and other species (including celery, lettuce, Swiss chard, spinach, squash, tomato, chili pepper, eggplant, and perennial ryegrass) exhibit the highest demand and transport rate of this non-assimilable mineral nutrient to maximise growth of these herbaceous and also woody (such as citrus and olive) species. While Cl- promotes cell expansion across all growth stages, its particularly pronounced stimulation of plant growth during EVD is associated with enhanced photosynthetic performance and PSII activity. This enhancement is in turn linked to a reduction in non-regulated energy dissipation in PSII and an increase in the electron transport rate, along with ultrastructural changes in chloroplasts, underscoring that Cl- is specifically required during EVD to drive the maturation of the photosynthetic apparatus. Unlike adult plants, the growth deficiencies caused by sub-macronutrient Cl- levels during EVD cannot be mitigated by equivalent nitrate (NO3 -) supplementation. As EVD concludes, plant demand for Cl- gradually decreases, accompanied by a reduced growth response to Cl- and an increased reliance on NO3 -, emphasising stage-specific nutrient needs. The relevance of Cl- as a morphogenic driver during a critical stage of development has significant implications for optimizing agronomic practices, particularly by reducing dependence on nitrogen fertilisers.

In the 19th century it was proposed that ecophysiology was best studied in regions with extreme climatic conditions. In the present perspective, we argue that perhaps this is more timely than ever. The main reason is the need to improve crops to be simultaneously more productive-due to the increased population-and more stress tolerant-due to climate change. Climate change induces plants to face not just harsh but also 'unexpected' (unpredictable) climatic conditions. In this sense, we hypothesize that 'sherplants', namely plants living in the extremes of plant life (e.g. hot deserts, Arctic and Antarctica, or high elevations) can provide cues on how to break the trade-off between productivity and stress tolerance, as they need to be produced quickly due to the very short growing period while being stress tolerant due to the harsh and unpredictable climate endured during most of the year. We present glimpses of results from three consecutive projects developed over the last 10 years, in which hundreds of species from different regions of the world have been studied. In particular, we propose a pathway for developing 'shercrops' learning from 'sherplants', debate whether some of the already studied species may have really broken the aforementioned trade-off, and present a number of interesting unforeseen discoveries made when studying plants from extreme climates.

Crop plants, including fruit trees, are particularly vulnerable to water scarcity because past selection prioritized productivity over drought resistance, making it challenging to maintain productivity with minimal water use in the context of climate change. This study aims to determine which trait combination of 10 fruit tree species influences their water and carbon use, with the goal of understanding their adaptability to water scarcity. The results showed that water stress traits (turgor loss point, TLP; vulnerability index, VI), a carbon-related trait (specific leaf area; SLA), and a biomass allocation trait (Huber value; Hv) define the major axis of variability and present the strongest correlations with other traits. Two distinct strategies emerged: the first, mainly around Prunus species, was characterized by high Hv, low SLA, more negative TLP, and low VI, indicating greater water-stress tolerance due to sapwood redundancy and reduced organ vulnerability. They also exhibited higher maximum photosynthetic rates, indicating greater assimilation rates. The second strategy, mainly including Citrus species, exhibited opposite traits and trends. These trait combinations were likely shaped by shared ancestry and environmental factors. Understanding these correlations can guide irrigation practices and the selection of resilient species, contributing to more robust agricultural systems in a changing climate scenario.

The rapidity with which stomata respond to environmental stresses, such as water shortages or changes in atmospheric demand, is crucial for plant survival and increased water use efficiency. We still have limited information on how the anatomy of stomatal complexes relates to physiological variables, such as transpiration or leaf turgor pressure, and thus to their overall response kinetics. We hypothesize that the coordination between the anatomy of the stomatal complex and transpiration influences the speed of stomatal response to environmental stress by affecting turgor pressure dynamics. To test this, we grew tomato plants under different levels of atmospheric demand, or water vapour pressure deficit (VPD), to generate different leaf anatomies in terms of stomatal complexes, as well as to assess their physiological behaviour. We found that plants grown under high evaporative demand developed leaves with smaller stomatal size: epidermal cell size ratio (SS:ECS), higher steady state leaf turgor pressure (Ψp-st), and transpiration rates (Est) than those grown at low VPD, leading to faster stomatal responses to leaf excision, as well as shorter response durations, which were found to be correlated with an increase in the cumulative water use efficiency during the response. We attribute this stomatal kinetics to a fine coordination between these anatomical changes in the stomatal complex and specific physiological traits (Est, Ψp-st), needed for the plants to exhibit such a faster stomatal response. These results highlight the significance of effective coordination between the anatomy of the stomatal complex and associated physiological parameters in optimising stomatal regulation.

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 on transpiration, stomatal conductance, and hydraulic traits. We measured sap flux density (Js), stomatal conductance (gs), and different hydraulic traits in five crop species. Our aim was to contribute to establishing 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 analysed. Particularly 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. The Hv was also significantly related to the slope of the relationship between gs and Js response to vapour pressure deficit and explained most of its variability, adding up to evidence recognizing Hv as a major trait in plant water relations. Thus, a hydraulic basis for regulation of tree water use should be considered.

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.

This is an overview of the work of our research group, the Irrigation and Crop Ecophysiology group, on new approaches for precision irrigation in a frame of digital agriculture. We first address advances in crop sensing and digitalization to better face the challenge of producing more with less inputs and to foster Intensive Sustainable Agriculture. Then we focus on new sensors and data processing methodologies, and on the development of models and expert systems for precision irrigation in digitalized orchards. We finish with an analysis of the growers' willingness to adopt new technologies for smart irrigation.

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 (AN), stomatal conductance (gs), leaf osmotic potential (Ψπ), 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. Ψπ 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 Ψπ. Thus, the sugar accumulation would have had a dual effect because on one hand, it decreased Ψπ, and on the other hand, it would have downregulated AN, and finally gs in WW trees. Interestingly, the modification of Ψπ 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 great help for fruit orchard management in the future.

This is an overview of the work of our research group, the Irrigation and Crop Ecophysiology group, on new approaches for precision irrigation in a frame of digital agriculture. We first address advances in crop sensing and digitalization to better face the challenge of producing more with less inputs and to foster Intensive Sustainable Agriculture. Then we focus on new sensors and data processing methodologies, and on the development of models and expert systems for precision irrigation in digitalized orchards. We finish with an analysis of the growers’ willingness to adopt new technologies for smart irrigation.

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 AN-Ci was analyzed to assess the maximum carboxylation rate (Vcmax), maximum rate of electron transport (Jmax), 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 Jmax and Vcmax 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.

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.

Precision irrigation is technically demanding and expensive, limitation that can be alleviated with leaf turgor pressure sensors (ZIM probes, also known as Yara-water sensors) as one of the promising tools for both monitoring plant water status and irrigation scheduling. Although ZIM probes have shown to be useful to schedule a regulated deficit irrigation strategy in a commercial olive orchard, this irrigation approach presents limitations beyond a certain level of water stress (ca. Psi(stem)<-1.7 MPa), when sensor readings are apparently no longer related to leaf turgor, which makes the sensor useless for irrigation scheduling in certain periods of the olive growing cycle. Here, we present results of an experiment with two-year old olive (Olea europaea 'Arbequina') potted trees in which irrigation was withheld to achieve values of midday stem water potential (Psi(stem)) below -1.7 MPa. The trees were monitored continuously with both ZIM probes and leaf thickness sensors. The aim of this work was to assess the actual significance of the ZIM probe records at high levels of water stress to establish new indicators for irrigation scheduling in periods of severe drought. Our results confirm that the relationship between the indicators derived from ZIM probe readings and Psi(stem), that were stablished to schedule the stablished regulated deficit irrigation strategy, hold for 'Arbequina' olive trees under different environmental conditions. In addition, our results showed an agreement between diel dynamics in ZIM probe records and leaf thickness measurements, suggesting that the ZIM probe could be useful for irrigation scheduling of trees under severe water stress.

Leaf water potential (ψleaf ), 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 ψleaf (ψleafPC ) 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 ψleafPC from multiple laboratories, and synthesized experiments testing common assumptions and practices in ψleafPC for diverse species: (i) the need for equilibration of previously transpiring leaves; (ii) leaf storage before measurement; (iii) the equilibration of ψleaf for leaves on bagged branches of a range of dehydration; (iv) the equilibration of ψleaf across the lamina for bagged leaves, and the accuracy of measuring leaves with artificially 'elongated petioles'; (v) the need in ψleaf 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 ψleafPC 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.