Plant Water Status Research Articles

Silicon nanoparticles in higher plants: Uptake, action, stress tolerance, and crosstalk with phytohormones, antioxidants, and other signalling molecules

Silicon is absorbed as uncharged mono-silicic acid by plant roots through passive absorption of Lsi1, an influx transporter belonging to the aquaporin protein family. Lsi2 then actively effluxes silicon from root cells towards the xylem from where it is exported by Lsi6 for silicon distribution and accumulation to other parts. Recently, it was proposed that silicon nanoparticles (SiNPs) might share a similar route for their uptake and transport. SiNPs then initiate a cascade of morphophysiological adjustments that improve the plant physiology through regulating the expression of many photosynthetic genes and proteins along with photosystem I (PSI) and PSII assemblies. Subsequent improvement in photosynthetic performance and stomatal behaviour correspond to higher growth, development, and productivity. On many occasions, SiNPs have demonstrated a protective role during stressful environments by improving plant-water status, source-sink potential, reactive oxygen species (ROS) metabolism, and enzymatic profile. The present review comprehensively discusses the crop improvement potential of SiNPs stretching their role during optimal and abiotic stress conditions including salinity, drought, temperature, heavy metals, and ultraviolet (UV) radiation. Moreover, in the later section of this review, we offered the understanding that most of these upgrades can be explained by SiNPs intricate correspondence with phytohormones, antioxidants, and signalling molecules. SiNPs can modulate the endogenous phytohormones level such as abscisic acid (ABA), auxins (IAAs), cytokinins (CKs), ethylene (ET), gibberellins (GAs), and jasmonic acid (JA). Altered phytohormones level affects plant growth, development, and productivity at various organ and tissue levels. Similarly, SiNPs regulate the activities of catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), and ascorbate-glutathione (AsA-GSH) cycle leading to an upgraded defence system. At the cellular and subcellular levels, SiNPs crosstalk with various signalling molecules such as Ca2+, K+, Na+, nitric oxide (NO), ROS, soluble sugars, and transcription factors (TFs) was also explained.

Salicylic acid mediated physiological and biochemical alterations to confer drought stress tolerance in Zinnia ( Z. elegans )

Background: Protective role of salicylic acid against drought has been widely reported, but its effects on Zinnia elegans remain unknown.
 Hypotheses: Foliar salicylic acid (SA) improves water status, pigments, and antioxidant systems of Zinnia plants under drought stress.
 Studied species: Z. elegans (cv. Dreamland) were purchased from Chanan Seeds Store Lahore, Pakistan.
 Study site and dates: MNS University of Agriculture, Multan, Punjab, Pakistan; March-May, 2018.
 Methods: After two weeks of transplanting, one set of seedlings was exposed to drought stress (60 % field capacity, FC) while other control set was maintained at 100 % FC. Foliar SA (100 mg L-1) was applied to plants at drought initiation.
 Results: Foliar SA treatment to water stressed plants (60 % FC) increased the leaf area (46.89 cm2), shoot and root lengths (25 cm and 26.67 cm, respectively), leaf relative water content (75.98 %); chlorophyll a (0.68 mg g-1), chlorophyll b (0.38 mg g-1) and carotenoid concentrations (1.10 mg g-1); and catalase (116.67 U min-1 mg-1 protein), guaiacol peroxide (72 U min-1 mg-1 protein) and superoxide dismutase (93 U min-1 mg-1 protein) activities.
 Conclusions: Foliar SA could be used to minimize impacts of water stress in Zinnia plants.

A Novel Method to Simultaneously Measure Leaf Gas Exchange and Water Content

Understanding the relationship between plant water status and productivity and between plant water status and plant mortality is required to effectively quantify and predict the effects of drought on plants. Plant water status is closely linked to leaf water content that may be estimated using remote sensing technologies. Here, we used an inexpensive miniature hyperspectral spectrometer in the 1550–1950 nm wavelength domain to measure changes in silver birch (Betula pendula Roth) leaf water content combined with leaf gas exchange measurements at a sub-minute time resolution, under increasing vapor pressure deficit, CO2 concentrations, and light intensity within the measurement cuvette; we also developed a novel methodology for calibrating reflectance measurements to predict leaf water content for individual leaves. Based on reflectance at 1550 nm, linear regression modeling explained 98–99% of the variation in leaf water content, with a root mean square error of 0.31–0.43 g cm−2. The prediction accuracy of the model represents a c. ten-fold improvement compared to previous studies that have used destructive sampling measurements of several leaves. This novel methodology allows the study of interlinkages between leaf water content, transpiration, and assimilation at a high time resolution that will increase understanding of the movement of water within plants and between plants and the atmosphere.

Determining the plant critical saturated water accumulation curve in maize

Water scarcity is one of the major factors limiting crop growth and productivity. Judicious water management reduces the application of irrigation water and increases grain yield, farm profits, and water use efficiency . The assessment of crop water status is the key to in-season irrigation scheduling . The plant diagnostic approach has the potential to assess the in-season crop water status for optimizing crop water use. For this purpose, a series of field and rainout shelter experiments with varying amounts of irrigation water (0–275 mm for field and 0–315 mm for rainout shelter experiments) and planting densities (6–8 ×10 4 plants ha −1 ) using seven maize cultivars were conducted from the 2017–2020 growing seasons in North China Plain to determine and validate the plant critical saturated water accumulation (SWA) curve during the vegetative growth period of maize. The result showed that the plant dry mass (DM) and the SWA ranged from 0.07 to 8.22 t ha −1 and 0.63–59.06 t ha −1 during the vegetative growth period of maize, respectively. The plant DM and SWA increased with the increase in irrigation amount. However, plant DM and plant SWA showed non-significant differences under non-water-limiting conditions. An allometric relationship between plant DM and plant SWA was used to develop the plant critical SWA curve (SWA = 8.26DM 0.89 , R 2 =0.98 ** ). A plant water diagnosis index (WDI) was then derived using the critical SWA curve to quantitatively assess the in-season water status of maize. The WDI increased with the increase of irrigation amount and ranged from 0.72 to 1.26 with a value of 1, indicating an optimum plant water status. The newly developed curve could diagnose and categorize the water-limiting and non-water-limiting plant water status and can be employed for precision irrigation management during maize cultivation.

Evaluation of irrigation frequency on pineapple plants grown in greenhouse conditions

• Seasons affect the values of all the indicators (LCI, NDVI, SDD, RWC). • The sensitivity of the non-destructive indicator is higher than the destructive. • High and medium irrigation frequency show higher conversion of water into biomass. • High frequency shows higher crop water productivity at the end of vegetative cycle. The objectives of this work are to evaluate the water status and growth variables of pineapple plants under different frequencies of irrigation to optimize the water productivity irrigation in greenhouse conditions in the subtropics. The experiment was conducted during the vegetative cycle for nine months, comparing three frequencies of irrigation: irrigation every three days (High frequency-T1), every seven days (Medium frequency-T2), and every 15 days (Low frequency-T3). The water status was measured using destructive indicators: Relative Water Content (RWC) and non-destructive indicators: Normalized Difference Vegetation Index (NDVI), Stress Degree Day (SDD), and Leaf Chlorophyll Index (LCI). Water productivity indicators (Irrigated water productivity, crop water productivity) and growth variables (plant height, maximum diameter, plant biomass, assimilate partitioning) were also measured. The environmental conditions monitored were temperature, humidity, and incident radiation. The soil moisture depletion and daily depletion rate were also registered and calculated. Destructive indicators of water status did not detect differences between irrigation treatments in this study, while non-destructive indicators statistically differentiated T1 from T3. T2 was the most appropriate irrigation treatment during the cold season. These results suggest that in greenhouse conditions in subtropical environments, a combination of high frequencies in warm seasons and medium frequencies in cold seasons would adjust irrigation management according to the pineapple crop needs, optimizing irrigation water productivity.

Foliar water uptake in eight mangrove species: Implications of morpho-anatomical traits

There is growing evidence that foliar water uptake (FWU) positively contributes to the water status of plants. However, the morpho-anatomical traits and the mechanisms responsible for variations in FWU of mangrove leaves are poorly understood. We evaluated the relationship between FWU and morpho-anatomical traits in eight mangrove species (Avicennia germinans, A. marina, A. schaueriana, Bruguiera gymnorhiza, Conocarpus erectus, Laguncularia racemosa, Rhizophora mangle, R. mucronata). FWU was measured in leaves experimentally submerged in distilled water and was related to morphological and anatomical traits using a Principal Component Analysis (PCA). There were inter-species differences in FWU, with L. racemosa and A. schaueriana having the highest values, and B. gymnorhiza and R. mucronata having the lowest. Three groups associated at the family level were found based on morpho-anatomical attributes: (1) greater thickness of the abaxial epidermis and specific leaf area (L. racemosa and C. erectus; Combretaceae); (2) presence of trichomes and salt glands and thicker palisade parenchyma (A. germinans, A. marina, and A. schaueriana; Acanthaceae), both families with relatively high FWU; and (3) higher leaf dry mass, leaf area, and thicker hypodermis (B. gymnorhiza and R. mucronata; Rhizophoraceae), but lower FWU. Our results suggest that mangrove species take up atmospheric water at different rates and strategies that depend on morpho-anatomical traits, suggesting its differential use as a supplementary resource.

Water status and thermal response of lime trees to irrigation and shade screen

Most lime trees are cultivated under open-field conditions. However, in the Mediterranean area some growers use shade screen to protect their orchards against abiotic and biotic stresses, inducing changes in the plant’s surrounding microclimate that could affect its water status. This field experiment focuses on the effect of shade screen (high density polyethylene white net with 76% light transmission) and irrigation on plant and soil water status of Bearss lime trees. Two irrigation treatments were applied during the summer-autumn to open-field and shaded lime trees: irrigated (control) and non-irrigated (stress). Volumetric soil water content (θv), air temperature (Ta) and canopy temperature (Tc) were real-time monitored and several derived thermal indices were calculated. Stem water potential (Ψstem) and leaf gas exchange: net photosynthesis (Pn) and stomatal conductance (gs) were measured on representative days. Withholding irrigation caused a gradual decline in soil and plant water status. θv decreased from the outset in the non-irrigated treatments, showing breaking point connecting the rapid and the slower soil drying processes. Significant differences in Ψstem, and gs values were observed between controls and stressed trees 15 days after stress initiation. During early stages of water stress, lime trees cultivated in open-field showed lower values of soil and plant water status than those grown in shaded conditions. However, at the end of stress period, similar values were noted for both cropping systems, pointing to severe water deficit. Tc and Tc-Ta values reflected the current lime tree water status. The soil water content sensors anticipated the plant water stress situation respect to thermal ones. The higher θv, Ψstem, gs, Pn and Tc values registered in shaded lime trees revealed that shading allowed better soil-plant water status and a 12-day window of opportunity to respond to the imposed soil water deficits. Threshold thermal-based values are proposed for precise irrigation management of lime trees in open-field and shaded conditions.

Combination of multispectral imagery, environmental data and thermography for on-the-go monitoring of the grapevine water status in commercial vineyards

Efficient irrigation in viticulture requires objective and representative monitoring of the vineyard water status variability. In this work the combination of multispectral, environmental and thermal data (using an infrared radiometer) acquired simultaneously on-the-go (at midday), from a ground moving vehicle (moving at 3 km/h) was tested to assess the vineyard stem water potential (Ψs) and its spatial variability (three different irrigation treatments were imposed) over two seasons in north Spain. Partial least squares (PLS) cross-validation regression models involving the canopy temperature (Tc), environmental and spectral variables yielded determination coefficients (R2cv) of ~ 0.63 and root mean square error of cross-validation (RMSECV) between 0.124 MPa and 0.206 MPa in the two seasons. Linear discriminant analysis (LDA) involving only the variables used to build the regression models was run to distinguish among low, medium and high water stressed vines, yielding an average percentage of correct classification samples of 74%. The satisfactory performance of the multivariate models involving thermal, environmental and spectral data to either estimate or classify the plant water status within a vineyard supports the approach towards the combination of different data source to improve the capabilities of thermography itself. The inclusion of vegetative spectral indices in the regression and classification models of grapevine water status may provide real-time feedback on grapevine water use as influenced by actual vegetative growth, abiotic and/or biotic stress patterns. This combined approach can be seen as an advancement from existing solutions to assess plant water status variability given the simplicity and potential to automation of the thermal sensor employed and the integration of environmental and canopy vigour data into the model.

Hydrogen Sulfide, Ethylene, and Nitric Oxide Regulate Redox Homeostasis and Protect Photosynthetic Metabolism under High Temperature Stress in Rice Plants.

Rising temperatures worldwide due to global climate change are a major scientific issue at present. The present study reports the effects of gaseous signaling molecules, ethylene (200 µL L−1; 2-chloroethylphosphonic acid; ethephon, Eth), nitric oxide (NO; 100 µM sodium nitroprusside; SNP), and hydrogen sulfide (H2S; 200 µM sodium hydrosulfide, NaHS) in high temperature stress (HS) tolerance, and whether or not H2S contributes to ethylene or NO-induced thermo-tolerance and photosynthetic protection in rice (Oryza sativa L.) cultivars, i.e., Taipei-309, and Rasi. Plants exposed to an HS of 40 °C for six h per day for 15 days caused a reduction in rice biomass, associated with decreased photosynthesis and leaf water status. High temperature stress increased oxidative stress by increasing the content of hydrogen peroxide (H2O2) and thiobarbituric acid reactive substance (TBARS) in rice leaves. These signaling molecules increased biomass, leaf water status, osmolytes, antioxidants, and photosynthesis of plants under non-stress and high temperature stress. However, the effect was more conspicuous with ethylene than NO and H2S. The application of H2S scavenger hypotaurine (HT) reversed the effect of ethylene or NO on photosynthesis under HS. This supports the findings that the ameliorating effects of Eth or SNP involved H2S. Thus, the presence of H2S with ethylene or NO can enhance thermo-tolerance while also protecting plant photosynthesis.

Physiological and molecular features predispose native and invasive populations of sweet briar (Rosa rubiginosa L.) to colonization and restoration of drought degraded environments

The aim of this study was to determine physiological and molecular grounds for high adaptation potential of invasive populations of Rosa rubiginosa to soil drought. We assume that the invasive populations possess specific and effective adaptive mechanisms making them capable pioneer and nurse plants in dry environments. By colonizing the land, they limit its degradation and initiate revitalization of areas damaged by soil droughts. We analyzed plant water status, the photosynthetic apparatus activity, carbohydrate and phenolic content, the level of non-enzymatic antioxidants and RbcL protein associated with fixation of CO2. The research involved native (Northern Hemisphere: Poland, Spain) and invasive (Southern Hemisphere: Argentine, New Zealand) populations. Contrary to the native population, the invasive one demonstrated soil drought induced specific responses aimed at maintaining high water potential in the leaves, greater content of soluble carbohydrates, and higher osmotic potential. In the invasive population, the accumulation of soluble carbohydrates prevailed over their consumption for the synthesis of phenolic compounds. The invasive plants also maintained high content of assimilation pigments and showed greater level of non-enzymatic antioxidants. Reduced activity of the photosynthetic apparatus was associated both with increased energy amount dissipated from PSII and the efficiency with which an electron can move from the reduced intersystem electron acceptors to the PSI end electron acceptors. The study results pave the path for further research on the genetic basis of sweet briar response to soil drought in the context of progressive steppe formation and desertification.

Deep learning for identification of water deficits in sugarcane based on thermal images

Thermal images of plants have been used as a way for monitoring water status since it does provide a non-destructive method that allows its remote evaluation. Even with the facilities provided, it does require a high level of expertise for a human to evaluate these images and this is a time-consuming task. In this context, machine learning techniques are crucial tools that can automatically evaluate the images and predict the water status of plants with more accuracy and as fast as possible to deal with the dynamic in time and space of agriculture fields. In this work, a method for the evaluation of thermal images of sugarcane crop predicting its water status is proposed. The method can be used to evaluate thermal images taken with any type of portable thermal camera available on the market today. For this an artificial neural network model is used, Inception-Resnet-v2 network, that is a kind of a deep learning model combined with the transfer learning technique that allow archive high accuracy with low time and cost, compared with traditional methods. The proposed model performance was compared to a human evaluating the same set of thermal images. Overall results showed that the developed system achieved superior performance compared to the assessments made by the human and aided in classifying the water stress of plant’s thermal images in a non-destructive manner. In addition to superior performance accuracy by 23 %, 17 %, and 14 % for the AWC classes of 25 %, 50 %, and 100 %, respectively, the deep learning model demonstrated a greater ability to distinguish between the classes of thermal stress. Thus, the system developed in this study is a less time-consuming, affordable, non-destructive and effective tool for estimating the water status of sugarcane plants in the field, based on thermal images.

SurEau-Ecos v2.0: a trait-based plant hydraulics model for simulations of plant water status and drought-induced mortality at the ecosystem level

Abstract. A widespread increase in tree mortality has been observed around the globe, and this trend is likely to continue because of ongoing climate-induced increases in drought frequency and intensity. This raises the need to identify regions and ecosystems that are likely to experience the most frequent and significant damage. We present SurEau-Ecos, a trait-based, plant hydraulic model designed to predict tree desiccation and mortality at scales from stand to region. SurEau-Ecos draws on the general principles of the SurEau model but introduces a simplified representation of plant architecture and alternative numerical schemes. Both additions were made to facilitate model parameterization and large-scale applications. In SurEau-Ecos, the water fluxes from the soil to the atmosphere are represented through two plant organs (a leaf and a stem, which includes the volume of the trunk, roots and branches) as the product of an interface conductance and the difference between water potentials. Each organ is described by its symplasmic and apoplasmic compartments. The dynamics of a plant's water status beyond the point of stomatal closure are explicitly represented via residual transpiration flow, plant cavitation and solicitation of plants' water reservoirs. In addition to the “explicit” numerical scheme of SurEau, we implemented a “semi-implicit” and “implicit” scheme. Both schemes led to a substantial gain in computing time compared to the explicit scheme (>10 000 times), and the implicit scheme was the most accurate. We also observed similar plant water dynamics between SurEau-Ecos and SurEau but slight disparities in infra-daily variations of plant water potentials, which we attributed to the differences in the representation of plant architecture between models. A global model's sensitivity analysis revealed that factors controlling plant desiccation rates differ depending on whether leaf water potential is below or above the point of stomatal closure. Total available water for the plant, leaf area index and the leaf water potential at 50 % stomatal closure mostly drove the time needed to reach stomatal closure. Once stomata are closed, resistance to cavitation, residual cuticular transpiration and plant water stocks mostly determined the time to hydraulic failure. Finally, we illustrated the potential of SurEau-Ecos to simulate regional drought-induced mortality over France. SurEau-Ecos is a promising tool to perform regional-scale predictions of drought-induced hydraulic failure, determine the most vulnerable areas and ecosystems to drying conditions, and assess the dynamics of forest flammability.

Exogenously Applied Proline Enhances Morph-Physiological Responses and Yield of Drought-Stressed Maize Plants Grown Under Different Irrigation Systems.

The exogenous application of osmoprotectants [e.g., proline (Pro)] is an important approach for alleviating the adverse effects of abiotic stresses on plants. Field trials were conducted during the summers of 2017 and 2018 to determine the effects of deficit irrigation and exogenous application of Pro on the productivity, morph-physiological responses, and yield of maize grown under two irrigation systems [surface irrigation (SI) and drip irrigation (DI)]. Three deficit irrigation levels (I100, I85, and I70, representing 100, 85, and 70% of crop evapotranspiration, respectively) and two concentrations of Pro (Pro1 = 2 mM and Pro2 = 4 mM) were used in this study. The plants exposed to drought stress showed a significant reduction in plant height, dry matter, leaf area, chlorophyll content [soil plant analysis development (SPAD)], quantum efficiency of photosystem II [Fv/Fm, Fv/F0, and performance index (PI)], water status [membrane stability index (MSI) and relative water content (RWC)], and grain yield. The DI system increased crop growth and yield and reduced the irrigation water input by 30% compared with the SI system. The growth, water status, and yield of plants significantly decreased with an increase in the water stress levels under the SI system. Under the irrigation systems tested in this study, Pro1 and Pro2 increased plant height by 16 and 18%, RWC by 7 and 10%, MSI by 6 and 12%, PI by 6 and 19%, chlorophyll fluorescence by 7 and 11%, relative chlorophyll content by 9 and 14%, and grain yield by 10 and 14%, respectively, compared with Pro0 control treatment (no Pro). The interaction of Pro2 at I100 irrigation level in DI resulted in the highest grain yield (8.42 t ha–1). However, under the DI or SI system, exogenously applied Pro2 at I85 irrigation level may be effective in achieving higher water productivity and yield without exerting any harmful effects on the growth or yield of maize under limited water conditions. Our results demonstrated the importance of the application of Pro as a tolerance inducer of drought stress in maize.

Effects of rising VPD on the nutrient uptake, water status and photosynthetic system of tomato plants at different nitrogen applications under low temperature

In winter and spring, the low-temperature and high-humidity environment of greenhouses in China and some locations are not suited for the development of tomatoes, which is sensitive to cold. At low temperature circumstances, the plant growth is slow, and the water transpiration ability is weak. The study tried to increase the vapor pressure deficit (VPD) by decreasing the humidity to observe if it can promote plant transpiration, which in turn facilitates nutrient absorption conveyed by the water, or it directly influences plant development through the alteration of the plant morphological structure. Two VPD levels (high VPD, HVPD; low VPD, LVPD) and three N supply gradients (low N level, LN; normal N level, NN; high N level, HN) were set in a climate chamber for 30 days test. We observed the physiological alterations of plants. The results revealed that biomass of low nitrogen, normal nitrogen and high nitrogen of HVPD plants decreased by 22.54%, 40.75% and 10.31%, respectively, compared with LVPD-treated plants. The palisade/spongy tissue ratio in leaves of HVPD plants decreased at normal and high nitrogen levels. Under HVPD conditions, the stomatal length and width increased, but its density decreased; the electron transfer and photochemical efficiency of the photosystem reaction center reduced. At low, normal and high nitrogen concentration, the photosynthetic rate of HVPD plants was 17.29%, 30.18% and 15.15% lower than that of LVPD plants. For HVPD plants, compared with LVPD plants, K+ absorption under LN increases significantly; nutritional absorption with HN treatment reduced significantly; the absorption of trace elements was also lower than LVPD plants. It revealed that even within the theoretically suitable VPD range for plant growth, rising VPD cannot achieve the purpose of improving nutrient absorption and stimulating growth. It needed to be examined according to certain environmental circumstances. In addition, the promotion impact of increasing N fertilizer was restricted, and it may not be favorable to plant development. At low nitrogen, LVPD treated plants thrived nicely, compared with HVPD treated plants. The investigation revealed that the optimal growth treatment at low temperature was LVPD+NN treatment.

Optimal irrigation management for avocado (cv. 'Hass') trees by monitoring soil water content and plant water status

Irrigation scheduling based on soil water content (Ɵw) sensors requires that Ɵw be maintained within a range (management lines) that is optimal for plant growth. The lower limit or “breaking point” is determined following the soil water content dynamics on the transition of a rapid rate of depletion to a slower, under similar reference evapotranspiration. Although this criterion is practical, its implementation should be validated with plant water status measurement that contemplate weather condition, such as stem water potential “non-stressed” baseline (Ψₓ as a function of vapor-pressure deficit (VPD) in Ɵw conditions that do not limit yield). A study was conducted on a mature cv. ‘Hass’ avocado orchard in Central Chile during two seasons. There were 5 irrigation treatments: T1, Control; T2 and T3 with 29% less and 25% more of what was applied in T1, respectively; T4 and T5 same as Control until first and second fruit drop abscission, respectively, and then with 29% less. T1 trees were irrigated using a continuous frequency domain reflectometry (FDR) probe to maintain the root zone between field capacity and the breaking point. There was biweekly monitoring of the Ɵw prior to irrigation, Ψₓ and VPD. The Ψₓ decline proportional to the intensity and the timing of water restriction; however, no treatment affected the crop load in either season. T2 did not show significant detrimental in fruit size, production and maturation, despite that frequently reached water content levels at the limit of the breaking point, and showed lower levels of stem water potential than Control, being the treatment with the highest water productivity. The results confirm that breaking point is an effective criterion to establish irrigation management. Additionally, when comparing the baseline for our non-stressed trees with a baseline from full irrigation treatments obtained from the literature, 30% water savings were achieved.

Monitoring plant water status via static uniaxial compression of the leaf lamina.

Turgor pressure is an essential, but difficult to measure indicator of plant water status. Turgor has been quantified by localized compression of cells or tissues, but a simple method to perform these measurements is lacking. We hypothesized that changes in leaf turgidity can be monitored by uniaxially compressing the leaf lamina and measuring the mechanical stress under a constrained thickness (stress relaxation)and that changes in leaf water content can be monitored by measuring the leaf thickness under constant mechanical stress. Using a simple, custom-built leaf squeeze-flow rheometer, we performed different compression tests on leaves from 13 plant species. The mechanical stress measured during stress relaxation was correlated with leaf bulk turgor pressure (R2 > 0.95) and thus with balancing pressure (R2 > 0.94); the leaf thickness measured under constant mechanical stress was correlated with relative water content (R2 > 0.74). The coefficients of these relationships were related to the leaf bulk osmotic pressure at the turgor-loss point. An idealized average-cell model suggests that, under isothermal conditions, the stationary bulk modulus during compression is largely determined by the bulk osmotic pressure. Our study presents an inexpensive, accessibleand automatable method to monitor plant water status noninvasively.

Shade net and mulching measures for improving soil and plant water status of fig trees under rainfed conditions

Prolonged drought conditions and soil desiccation have caused extensive damage and reduction in yields of the largest rain-fed fig trees (Ficus carica L. ‘Sabz’) grove located in the semi-arid region of Estahban, Iran. In this experiment, the effect of suspended shade net and two types of water penetration systems covered with organic mulch on plant water status and productivity of the rain-fed fig trees on the foothill slopes with traditional micro-catchment were investigated during 2018–2020. The first experimental factors included -(Ctrl.) without shade net and -(S) covering the tree canopy with 25% shade intensity white suspended shade net; and the second experimental factors included -(Ctrl.) the local traditional practice (25 m2 bare soil micro-catchment only), -(M) application of wheat straw as organic mulch under the tree canopy with two concentrating infiltration pipes and -(MP) application of wheat straw mulch over the soil under the tree canopy with two concentrating infiltration pipes and on the surface of 4 m of overall plowing rows perpendicular to the slope to a depth of 40 cm and a width of 3 m at a distance of 2.5 m upslope of the tree trunk. MP treatment significantly increased and retained the average of soil moisture content by 79.9% in comparison with the local traditional practice. The results showed that S+MP had the greatest effect on inducing the physiological attribute of fig trees such as leaf stomatal conductance (121.1%), leaf transpiration (52.5%), leaf light-saturated net CO2 assimilation (96.6%) and the leaf water potential (30.9%) as the main effective variable in association with increment of commercial fruit yield. This treatment had the highest impacts on the increment of yield (187.7%) and commercial and healthy quality of ‘Sabz' fig dry fruit under severe drought conditions in rain-fed orchards.

Response of Potted Citrus Trees Subjected to Water Deficit Irrigation with the Application of Superabsorbent Polyacrylamide Polymers

Searching for new strategies to mitigate the effects of low water availability for citrus production, a study was carried out on potted mandarin cv. W. Murcott, with the objective of evaluating the physiological and growth response of the plants to polyacrylamide gel application in the substrate in water restriction conditions. The following treatments were evaluated, T0 (control) with 100% ETc water replenishment, T1 with 50% ETc water replenishment, and T2 with 50% ETc water replenishment plus the application of polyacrylamide polymers to the substrate. Temperature and water volumetric content (ϴ: m3 m−3) were evaluated in the substrate. Plant water-status parameters such as stem water potential (SWP), stomatal conductance (gs), and chlorophyll fluorescence (Fv/Fm), as well as biomass, nutrients levels, and proline biosynthesis were measured in the plants in response to the treatments. The results showed that the substrate moisture for T2 was kept significantly higher than T0 and T1, despite receiving the same irrigation rate as T1 and a half of T0; however, this higher moisture availability in the substrate of T2 was not reflected in the plant’s water status or growth. On the contrary, the T2 plants showed responses such as lower total biomass, lower vegetative development, and lower root biomass, as well as a higher concentration of proline in the root. According to these results, it is concluded that polymers such as polyacrylamide sodium allow the retention of water in the substrate, but do not necessarily release that water for plants, probably because that moisture is kept in the hydrogel and not released to the substrate media or the roots, or if released, in this case, this occurs with an increase in the concentration of sodium available to the plants, which could lead the citrus crop to a worse situation of water and/or osmotic stress.

Physiological and Structural Responses to Prolonged Water Deficit in Young Trees of Two Olive Cultivars.

This study aimed to characterize the physiological and structural responses of potted one-year-old olive trees belonging to two olive cultivars—‘Nocellara del Belice’ and ‘Cerasuola’—exposed to prolonged drought under greenhouse conditions. Two irrigation treatments based on evapotranspiration (ET) were imposed for 69 days, i.e., well-watered (WW, 100% ET) and drought-stressed (DS, 10–30% ET). Leaf stomatal conductance (gs), stem water potential (Ψstem), transpiration (E), photosynthetic capacity (Amax), water use efficiency (WUE), stem (Kstem) and root (Kroot) hydraulic conductance, trunk diameter variations (TDV), and leaf patch attenuated pressure fluctuations (pp, a proxy of the inverse of leaf turgor pressure) were measured in WW and DS trees at different stages of the experiment. Leaf gs did not significantly differ between cultivars under DS, whereas differences in Ψstem only became significant at the end of prolonged drought, when ‘Nocellara del Belice’ experienced Ψstem < −4 MPa. ‘Cerasuola’ trees expressed the best WUE under drought, although they were more susceptible to photoinhibition under optimal plant water status. Both cultivars tended to increase their Kstem at the end of the drought period. A marked reduction in Kroot occurred in ‘Cerasuola’ plants after prolonged drought; however, a similar mechanism was not observed in ‘Nocellara del Belice’. The ratio between Kstem and Kroot exponentially increased towards the end of the prolonged drought period in both cultivars, but more markedly in ‘Cerasuola’. TDV and pp trends suggested that ‘Cerasuola’ plants keep better plant water status under severe drought compared to ‘Nocellara del Belice’ by maintaining high leaf turgor and reduced trunk diameter fluctuations. These responses may be related to reduced cell wall elasticity and xylem vessel size and/or wall thickness—drought avoidance mechanisms. The Kstem/Kroot ratio can serve as an indicator of drought stress avoidance mechanisms to compare genotype-specific responses to drought stress.

Application of Phenomics to Elucidate the Influence of Rootstocks on Drought Response of Tomato

The cultivation of nutritionally and economically important crops like tomato are often threatened by dry spells due to drought as these crops largely depend on an assured water supply. The magnitude and intensity of drought is predicted to intensify under climate change scenarios, particularly in semi-arid regions, where water is already a scarce resource. Hence, it is imperative to devise strategies to mitigate the adverse effects of drought on tomato through improvement in the plant’s efficiency to utilise the moisture in the growth medium. Since the root is the entry point for water, its intrinsic structure and functions play a crucial role in maintaining the soil–water–plant continuum during moisture deficit at the rhizosphere. Grafting offers a great opportunity to replace the root system of the cultivated tomato plants with that of wild species and hence provide a rapid solution to modulate root system architecture in contrast to the time-consuming conventional breeding approach. However, the success in developing the best graft combination of cultivated tomato and rootstock depends on the source of rootstock and selection methods. In this study, we used a high throughput phenomics facility to assess the efficiency of tomato, grafted on the rootstocks of different genetic backgrounds, at different levels of moisture in the soil. Rootstocks included tomato cultivars and the hybrids, derived from the crosses involving wild relatives, as donor parents. Among the rootstocks, an interspecific (Solanum lycopersicum × S. pennellii) derivative RF4A was highly efficient in terms of productive use of water. The RF4A rootstock-grafted plants were more conservative in water use with higher plant water status through relatively better stomatal regulation and hence were more efficient in generating greater biomass under water stress conditions. These plants could maintain a higher level of PSII efficiency, signifying better photosynthetic efficiency even under water stress. The distinct response of interspecific rootstock, RF4A, to water stress can be ascribed to the effective root system acquired from a wild parent (S. pennellii), and hence efficient water uptake. Overall, we demonstrated the efficient use of a phenomics platform and developed a protocol to identify promising rootstock–scion combinations of tomato for optimization of water use.