Leaf Stomatal Conductance Research Articles

The light spectrum differentially influences morphology, physiology and metabolism of Chrysanthemum × morifolium without affecting biomass accumulation

AbstractThe development of light emitting diodes (LED) gives new possibilities to use the light spectrum to manipulate plant morphology and physiology in plant production and research. Here, vegetative Chrysanthemum × morifolium were grown at a photosynthetic photon flux density of 230 μmol m−2 s−1 under monochromatic blue, cyan, green, and red, and polychromatic red:blue or white light with the objective to investigate the effect on plant morphology, gas exchange and metabolic profile. After 33 days of growth, branching and leaf number increased from blue to red light, while area per leaf, leaf weight fraction, flavonol index, and stomatal density and conductance decreased, while dry matter production was mostly unaffected. Plants grown under red light had decreased photosynthesis performance compared with blue or white light‐grown plants. The primary and secondary metabolites, such as organic acids, amino acids and phenylpropanoids (measured by non‐targeted metabolomics of polar metabolites), were regulated differently under the different light qualities. Specifically, the levels of reduced ascorbic acid and its oxidation products, and the total ascorbate pool, were significantly different between blue light‐grown plants and plants grown under white or red:blue light, which imply photosynthesis‐driven alterations in oxidative pressure under different light regimens. The overall differences in plant phenotype, inflicted by blue, red:blue or red light, are probably due to a shift in balance between regulatory pathways controlled by blue light receptors and/or phytochrome. Although morphology, physiology, and metabolism differed substantially between plants grown under different qualities of light, these changes had limited effects on biomass accumulation.

Extreme drought can deactivate ABA biosynthesis in embolism-resistant species.

The phytohormone abscisic acid (ABA) is synthesised by plants during drought to close stomata and regulate desiccation tolerance pathways. Conifers and some angiosperms with embolism-resistant xylem show a peaking-type (p-type) response in ABA levels, in which ABA levels increase early in drought then decrease as drought progresses, declining to pre-stressed levels. The mechanism behind this dynamic remains unknown. Here, we sought to characterise the mechanism driving p-type ABA dynamics in the conifer Callitris rhomboidea and the highly drought-resistant angiosperm Umbellularia californica. We measured leaf water potentials (Ψl ), stomatal conductance, ABA, conjugates and phaseic acid (PA) levels in potted plants during a prolonged but non-fatal drought. Both species displayed a p-type ABA dynamic during prolonged drought. In branches collected before and after the peak in endogenous ABA levels in planta, that were rehydrated overnight and then bench dried, ABA biosynthesis was deactivated beyond leaf turgor loss point. Considerable conversion of ABA to conjugates was found to occur during drought, but not catabolism to PA. The mechanism driving the decline in ABA levels in p-type species may be conserved across embolism-resistant seed plants and is mediated by sustained conjugation of ABA and the deactivation of ABA accumulation as Ψl becomes more negative than turgor loss.

Foliar Pectins and Physiology of Diploid and Autotetraploid Mango Genotypes under Water Stress.

The cultivation of mango in Mediterranean-type climates is challenged by the depletion of freshwater. Polyploids are alternative genotypes with potential greater water use efficiency, but field evaluations of the anatomy and physiology of conspecific adult polyploid trees under water stress remain poorly explored. We combined field anatomical evaluations with measurements of leaf water potential (Ψl) and stomatal conductance (Gs) comparing one diploid and one autotetraploid tree per treatment with and without irrigation during dry summers (when fruits develop). Autotetraploid leaves displayed lower Ψl and Gs in both treatments, but the lack of irrigation only affected Gs. Foliar cells of the adaxial epidermis and the spongy mesophyll contained linear pectin epitopes, whereas branched pectins were localized in the abaxial epidermis, the chloroplast membrane, and the sieve tube elements of the phloem. Cell and fruit organ size was larger in autotetraploid than in diploid mango trees, but the sugar content in the fruits was similar between both cytotypes. Specific cell wall hygroscopic pectins correlate with more stable Ψl of autotetraploid leaves under soil water shortage, keeping lower Gs compared with diploids. These preliminary results point to diploids as more susceptible to water deficits than tetraploids.

Effects of AMF inoculation on the growth, photosynthesis and root physiological morphology of root-pruned Robinia pseudoacacia seedlings.

Root pruning hinders the absorption and utilization of nutrients and water by seedlings in the short term. Arbuscular mycorrhizal fungi (AMF) are an important source of nutrient and water for seedlings except for the root system. However, the mechanism by which AMF affect the physiological growth of seedlings after root pruning has rarely been studied. In this study, a pot experiment was conducted through a three-compartment partition system to clarify the effects of Funneliformis mosseae (F. mosseae) strain BGC XJ07A on the physiological growth of root-pruned Robinia pseudoacacia seedlings. Five root pruning treatments (zero, one-fifth, one-fourth, one-third and one-half of the taproot length were removed) were applied to noninoculated seedlings and those inoculated with F. mosseae. The results showed that the presence of F. mosseae significantly increased the shoot and root biomasses, leaf photosynthetic rate, stomatal conductance and transpiration rate. The root projected area, root surface area, average root diameter, root density, root volume and number of root tips of the inoculated seedlings were higher than those without inoculation in all root pruning treatments. The root cytokinin, gibberellins and indole-3-acetic acid concentrations, but root abscisic acid concentration, were higher than those measured in the absence of inoculation in all root pruning treatments. Moreover, the changes in the root endogenous hormone concentrations of the seedlings were closely related to the root morphological development and seedling biomass. The AMF increased the soil available nitrogen, soil available phosphorus, soil available potassium and soil organic matter concentrations compared with the noninoculated treatment. These results indicate that AMF can alleviate the adverse effects of root pruning on the physiological growth of R. pseudoacacia and soil properties, and can provide a basis for AMF application to forest cultivation and the sustainable development of forest ecosystems.

Spectral composition of LED light differentially affects biomass, photosynthesis, nutrient profile, and foliar nitrate accumulation of lettuce grown under various replacement methods of nutrient solution.

To enhance crop yield and quality, plant cultivation in controlled-growing systems is an alternative to traditional open-field farming. The use of light-emitting diode (LED) as an adjustable light source represents a promising approach to improve plant growth, metabolism, and function. The objective of this study was to assess the impact of different light spectra (red, red/blue (3:1), blue, and white) with an emission peak of around 656, 656, 450, and 449 nm, respectively, under various replacement methods of nutrient solution (complete replacement (CR), EC-based replacement (ECBR), and replacing based on plant needs (RBPN)), on biomass, physiological traits, and macro- and micronutrient contents of two best-known lettuce varieties, Lollo Rossa (LR) and Lollo Bionda (LB), in the nutrient film technique (NFT) hydroponic system. The results indicated that mix of red and blue LED spectra under RBPN method is the most effective treatment to enhance fresh and dry weights of lettuce plants. In addition, red LED spectrum under RBPN, and red and blue light under ECBR nutrient solution significantly increased leaf stomatal conductance, net photosynthesis and transpiration rate, and intercellular CO2 concentration of LR variety. Phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mn) content in LR variety, and iron (Fe), zinc (Zn), copper (Cu), and manganese (Mn) content in both varieties increased upon exposure to blue and red LED light spectrum with RBPN method. Our results suggest that exposure to combination of red and blue light along with feeding plants using RBPN and ECBR methods can increase absorption of macro- and micronutrient elements and improve photosynthetic properties, and eventually increase lettuce yield with lower nitrate accumulation.

Leaf morpho-physiological traits of Populus sibirica and Ulmus pumila in different irrigation regimes and fertilizer types.

The impacts of climate change, such as increased soil dryness and nutrient deficiency, highlight the need for environmentally sustainable restoration of forests and groundwater resources. However, it is important to consider that extensive afforestation efforts may lead to a depletion of groundwater supply due to higher evapotranspiration rates, exacerbating water scarcity issues. Consequently, we conducted a study to examine how the fast-growing tree species Populus sibirica (Horth ex Tausch) and Ulmus pumila (L.) respond morpho-physiologically to varying watering regimes and types of fertilizers, aiming to better understand their specific water and nutrient requirements. We used two-year-old nursery-growth seedlings (N=512) of P.sibirica and U. pumila with initial root collar diameter (RCD) and the height of 0.51±0.02mm and 68±2.94 cm and 0.33±0.01mm and 51±1.14 cm, respectively. The leaf area (LA), specific leaf area (SLA), chlorophyll concentration, stomatal conductance (gs), chlorophyll fluorescence, and predawn and midday leaf water potential were measured across treatments. Four different irrigation regimes and two different fertilizer types were applied: no irrigation (control, 0 L h-1), 2 L h-1 = 0.25 mm m-2, 4L h-1 = 0.5mm m-2, 8 L h-1 = 1.0 mm m-2 and 120 g and 500 g tree-1 of NPK and compost (COMP). Twelve plots (600 m2) were established in the study site for each species and treatments. During the first growing season (2021), the LA of P. sibirica was larger in the 4-8 L h-1 without fertilizer, but it was smaller in the 4 L h-1+ COMP during the second growing season (2022). The 2 L h-1 without fertilizer and 2 L h-1 + NPK had larger LA compared with the control (CONT) for the first and second growing seasons, respectively, for U. pumila. P. sibirica seedlings at 4 L h-1 without fertilizer had the highest SLA for 2021 and at 2 L h-1 + NPK for 2022, whereas CONT and 4 L h-1 had the highest SLA than the other treatments for 2021 and 2022 growing seasons, respectively, for U. pumila. The chlorophyll concentration of P. sibirica seedlings in the first year was generally higher in CONT, while the 2 L h-1 without any fertilizer yielded a significantly higher chlorophyll concentration of U. pumila. Chlorophyll fluorescence parameters (PIABS and Fm) were generally lower in CONT with/without NPK or COMP for both species. The CONT with NPK/COMP generally had a higher gs compared with the other treatments in both experimental periods for U. pumila, whereas CONT and 2 L h-1+ NPK-treated P. sibirica seedlings had a significantly greater gs during the first year and second year, respectively. The predawn and midday leaf water potentials of both species were generally the lowest in CONT, followed by 2 L h-1+ NPK/COMP during the first growing season, but a different pattern was observed during the second growing season. Overall, the morpho-physiological traits of the two species were affected by watering and fertilizer treatments, and the magnitude of the effects varied depending on growing season, amount of irrigation, and fertilizer type, and their interactions.

Response of Hydraulic and Photosynthetic Characteristics of Caroxylon passerinum (Bunge) Akhani and Roalson to Prolonged Drought and Short-Term Rehydration

Hydraulic traits are essential functional characteristics of plants related to water absorption, transport, and loss, serving as indicators of a plant’s adaptability to prevailing environmental water conditions. However, the hydraulic traits of shrub, particularly desert plants in arid and semi-arid regions, have been underexplored. In this study, we conducted a pot experiment using Caroxylon passerinum (Bunge) Akhani and Roalson as the subject. Three treatment groups were established: adequate water supply, mild drought, and severe drought. After subjecting the shrub to drought and subsequent rehydration, we measured hydraulic conductivity, net photosynthetic rate, and stomatal conductance. We found that leaf water potential decreased and stomatal conductance and net photosynthesis decreased with increasing drought intensity. We found that leaf water potential and stomatal conductance decreased with increasing drought intensity. Although there was no significant change in hydraulic conductivity in the two drought groups, the values were greater in the drought group than in the control, and greater in the mild drought group than in the severe drought group. Meanwhile, the embolism resistance decreased with increasing drought intensity. After rehydration, hydraulic conductivity did not return to control levels in the severe drought group, as did embolism resistance in the two drought groups, and leaf water potential did not recover significantly. The results showed that drought stress increased the hydraulic conductivity of C. passerinum, and this effect was more pronounced under mild drought stress. After the stress was lifted, C. passerinum continued to maintain a lower leaf water potential to promote water uptake. This result provides a reference for us to study water use of desert shrubs under different drought stresses.

Optimising fertigation of hydroponically grown sowthistle (Sonchus oleraceus L.): The impact of the nitrogen source and supply concentration

The efficient use of water and nutrients in leafy vegetable crops can be improved by effective water management, whereas the form of the supplied nitrogen may affect their quality and productivity. Sowthistle (Sonchus oleraceus L.), a widespread weed collected and consumed as a wild vegetable in the past, currently attracts a high interest for commercial cultivation due to its high nutritional value. The present study evaluated the effects of different nitrogen concentrations: N50: 50 mg L−1; (N 3.6 mmol L−1), N100: 100 mg L−1; (N 7.1 mmol L−1), N200: 200 mg L−1; (N 14.3 mmol L−1), and N300: 300 mg L−1; (N 21.4 mmol L−1) and different ammonium/total-N ratios (Nr: 0.01, 0.05, 0.10, 0.15) on growth, physiological parameters, antioxidant capacity and nutrient accumulation in the different plant parts of sowthistle, grown in Nutrient Film Technique hydroponic system. Total N was ammonium N plus nitrate N. Plant growth, total phenols, and antioxidant capacity were higher at the two intermediate N concentrations, whereas flavonoid and nitrogen content, as well as irrigation water productivity increased only with 200 mg N L−1 (N 14.3 mmol L−1), compared to the other three N concentrations. The accumulation of nitrogen in leaves and roots was lower, while leaf stomatal conductance was enhanced by increased N concentrations in the nutrient solution. Higher Nr ratios than ≥ 0.05 decreased plant dry matter, total phenols, flavonoids, and antioxidant capacity in leaf extracts, and negatively affected nitrogen translocation from roots to leaves. Sowthistle plants treated with a Nr of 0.05 exhibited a less intense oxidative stress, with decreased lipid peroxidation and hydrogen peroxide production, and increased superoxide dismutase and catalase activities, compared to those treated with higher Nr ratios. Increased Nr resulted in the accumulation of phosphorus and magnesium in leaves while the highest irrigation water productivity was obtained in plants grown with a Nr of 0.05. In conclusion, to increase yield, nutritional value and efficiency of water and nitrogen use in sowthistle grown in closed hydroponic systems, a N concentration of 200 mg L−1 of N (N 14.3 mmol L−1) and a Nr of 0.05 are suggested.

Cessation of berry growth coincides with leaf complete stomatal closure at pre-veraison for grapevine (Vitis vinifera) subjected to progressive drought stress.

Drought events have devasting impacts on grape berry production. The aim of this study was to investigate berry growth in the context of leaf stomatal closure under progressive drought stress. Potted grapevine plants (varieties 'Syrah' and 'Cabernet Sauvignon') were evaluated at pre-verasion (30-45 d after anthesis, DAA) and post-veraison (90-107 DAA). Berry diameter, berry absolute growth rate (AGR), leaf stomatal conductance (Gs) at midday, plant water potential at predawn and midday (ΨPD and ΨMD, respectively), and soil relative water content were measured repeatedly. The ΨPD-threshold of 90 % loss in stomatal conductance (Gs10, i.e. complete stomatal closure) was determined. Data were related to plant dehydration phases I, II and III with corresponding boundaries Θ1 and Θ2, using the water potential curve method. At pre-veraison, berry AGR declined together with leaf Gs in response to soil drying in both varieties. Berry AGR transitioned from positive to negative (shrinkage) values when leaf Gs approached zero. The Gs10-threshold was -0.81 MPa in 'Syrah' and -0.74 MPa in 'Cabernet Sauvignon' and was linked to boundary Θ1. At post-veraison, berry AGR was negligible and negative AGR values were not intensified by increasing drought stress in either variety. Leaf complete stomatal closure under progressive drought stress coincides with cessation of berry growth followed by shrinkage at pre-veraison (growth stage 1).

Silicon application mitigated the adverse effects of salt stress and deficit irrigation on drip-irrigated greenhouse tomato

Tomato (Solanum lycopersicum L.) is an important vegetable crop around the world, and water scarcity and soil salinization are two major unfavorable factors limiting the fruit yield and quality of greenhouse tomato in arid and semi-arid regions. The application of exogenous silicon has been reported to enhance tomato yield under salt or drought stress, but its effect under combined salt-drought stress remains unclear. A two-season (autumn 2021 and spring 2022) experiment was conducted with three irrigation levels (I1, 90%−100% θf, where θf is the field capacity; I2, 70%−80% θf; I3, 50%−60% θf), two soil salinity levels (S0, 0.1%, g/g; S1, 0.4%, g/g) and two silicon application rates (T0, 0 mM; T1, 2.4 mM) to explore their combined effects on leaf silicon content, photosynthetic parameters, fruit yield, nutrient yield, crop water productivity (WP), nitrogen uptake and utilization, nutrient water productivity (NWP) and economic benefit of drip-irrigated greenhouse tomato. The results showed that deficit irrigation and salt stress exerted significant inhibiting effects on leaf silicon content, photosynthetic parameters, tomato yield, and water-nitrogen productivity, but the inhibition was alleviated by silicon application, which increased leaf silicon content by 67.0%, net photosynthetic rate (Pn) by 25.3%, fruit yield by 12.3%, WP by 11.9%, nutrient yield by 10.0% (titratable acids) - 27.4% (soluble sugars) and NWP by 9.2% (titratable acids) - 26.1% (soluble sugars) on average. The average fruit yield over the two growing seasons was 66.01, 54.29 and 44.31 t ha−1 under I1, I2 and I3, and the silicon application increased average leaf silicon content by 71.9%, 65.2% and 63.0%, Pn by 11.1%, 12.9% and 7.6%, and fruit yield by 12.8%, 16.2%, and 8.1% at the three irrigation levels, respectively. Plant nitrogen uptake (NU) and nitrogen partial factor productivity (NPFP) increased but nitrogen use efficiency (NUE) tended to decrease with the increasing irrigation level, while silicon application improved NUE by 3.9% and 2.2% and NPFP by 13.8% and 11.7% in the two growing seasons, respectively. Silicon application significantly increased net profit by 24.3% and 17.7% in autumn 2021 and spring 2022, respectively. According to the principal component analysis, I1T1S0 ranked first in both growing seasons. The correlation matrix showed that fruit yield was positively correlated with leaf silicon content, Pn, stomatal conductance, WP, NU, NUE, NPFP, nutrient yield and net profit, while it had negative correlation with NWP. In conclusion, exogenous silicon application can improve the fruit yield and nutrient yield of drip-irrigated greenhouse tomato by enhancing leaf silicon content and photosynthetic capability under drought-stressed and salt-affected conditions.

Morphoanatomical Responses and Stomatal Conductance in Shaded and Sun-Exposed Broussonetia papyrifera Seedlings

Investigating invasive species’ morphoanatomical characteristics, such as leaf area and thickness of vascular tissues and storage cells, can reveal information about their adaptive ability and competitive advantage. Thus, we analyzed the variation in leaf, stem, and root morphoanatomical structure and stomatal conductance between shaded and sun-exposed seedlings of Broussonetia papyrifera to provide insights into management strategies to control its invasive ability. The variations in leaf area (LA), Leaf Mass per Area (LMA), stomatal density, thickness of palisade and spongy mesophyll tissues, thickness of xylem parenchyma cells, diameter of all xylem vessels in stem and roots and stomatal conductance were analyzed between shaded and sun-exposed seedlings. Results revealed that the LA and LMA of B. papyrifera were significantly larger in the sun-exposed than in the shaded condition. Seedlings exposed to sunlight also had thicker palisade mesophyll and xylem parenchyma cells. The diameter of xylem vessels in roots was also significantly higher in sun-exposed seedlings. Contrarily, a reverse pattern was observed in the diameter of stem xylem vessels (i.e., shaded > sun-exposed seedlings). Physiologically, a higher stomatal conductance was also observed in sun-exposed seedlings. In conclusion, we found significant variations in leaf, stem, and root morphoanatomy and stomatal conductance between shaded and sun-exposed seedlings of B. papyrifera. The findings of the present study may provide valuable implications for managing or controlling its invasibility in the introduced range. Keywords: freehand technique, invasive species, Moraceae, paper mulberry, stomatal conductance

Effects of simulated climate change conditions of increased temperature and [CO2] on the early growth and physiology of the tropical tree crop, Theobroma cacao L.

Despite multiple studies of the impact of climate change on temperate tree species, experiments on tropical and economically important tree crops, such as cacao (Theobroma cacao L.), are still limited. Here, we investigated the combined effects of increased temperature and atmospheric carbon dioxide concentration ([CO2]) on the growth, photosynthesis and development of juvenile plants of two contrasting cacao genotypes: SCA 6 and PA 107. The factorial growth chamber experiment combined two [CO2] treatments (410 and 700p.p.m.) and three day/night temperature regimes (control: 31/22°C, control+2.5°C: 33.5/24.5°C and control+5.0°C: 36/27°C) at a constant vapour pressure deficit (VPD) of 0.9kPa. At elevated [CO2], the final dry weight and the total and individual leaf areas increased in both genotypes, while the duration for individual leaf expansion declined in PA 107. For both genotypes, elevated [CO2] also improved light-saturated net photosynthesis (Pn) and intrinsic water-use efficiency (iWUE), whereas leaf transpiration (E) and stomatal conductance (gs) decreased. Under a constant low VPD, increasing temperatures above 31/22 °C enhanced the rates of Pn, E and gs in both genotypes, suggesting that photosynthesis responds positively to higher temperatures than previously reported for cacao. However, dry weight and the total and individual leaf areas declined with increases in temperature, which was more evident in SCA 6 than PA 107, suggesting the latter genotype was more tolerant to elevated temperature. Our results suggest that the combined effect of elevated [CO2] and temperature is likely to improve the early growth of high temperature-tolerant genotypes, while elevated [CO2] appeared to ameliorate the negative effects of increased temperatures on growth parameters of more sensitive material. The evident genotypic variation observed in this study demonstrates the scope to select and breed cacao varieties capable of adapting to future climate change scenarios.

Hydraulic traits and photosynthesis are coordinated with trunk sapwood capacitance in tropical tree species.

Water stored in trunk sapwood is vital for the canopy to maintain its physiological function under high transpiration demands. Little is known regarding the anatomical properties that contribute to the hydraulic capacitance of tree trunks and whether trunk capacitance is correlated with the hydraulic and gas exchange traits of canopy branches. We examined sapwood capacitance, xylem anatomical characteristics of tree trunks, embolism resistance, the minimal xylem water potential of canopy branches, leaf photosynthesis and stomatal conductance in 22 species from a tropical seasonal rainforest and savanna. The results showed that the mean trunk sapwood capacitance did not differ between the two biomes. Capacitance was closely related to the fiber lumen fraction and fiber wall reinforcement and not to the axial and ray parenchyma fractions. Additionally, it was positively correlated with the theoretical hydraulic conductivity of a trunk and the specific hydraulic conductivity of branches, and showed a trade-off with branch embolism resistance. Species with a high trunk sapwood capacitance maintained less negative canopy water potentials in the dry season, but higher leaf photosynthetic rates and stomatal conductance in the wet season. This study provides a functional link among trunk sapwood capacitance, xylem anatomy, canopy hydraulics and photosynthesis in tropical trees.

Effect of sowing dates on physiological characteristics, yield, and quality of Carthamus tinctorius

A field experiment was conducted to measure the physiological characteristics, yield, active ingredient content, and other indicators of Carthamus tinctorius leaves undergoing 13 sowing date treatments. The principal component analysis(PCA) and redundancy analysis were used to analyze the correlation between these indicators to explore the effect of sowing date on the yield and active ingredient content of C. tinctorius in Liupanshan of Ningxia. The results illustrated that the early sowing in autumn and spring had significant effects on leaf photosynthetic parameters, SPAD value, antioxidant enzyme activity, nitrogen metabolism enzyme activity, filament yield, grain yield, and hydroxy safflower yellow A(HYSA) of C. tinctorius. Sowing in mid-November and late March had the best effect. Leaf transpiration rate, stomatal conductance, nitrate reductase, nitrite reductase, glutamine synthetase, and glutamate synthase increased by 44.9%, 52.4%, 15.9%, 60.8%, 10.3%, and 38.3%, respectively. The activities of superoxide dismutase, peroxidase, and catalase decreased by 10.8%, 4.1%, and 20.9%, respectively. The improvement of photosynthetic physiological characteristics promoted the dry matter accumulation and reproductive growth of C. tinctorius. The yield of filaments and seeds increased by 15.5% and 11.7%, and the yield of HYSA and kaempferol increased by 17.9% and 20.0%. In short, the suitable sowing date can promote the growth and development of C. tinctorius in Liupanshan of Ningxia, and significantly improve the yield and quality, which is conducive to the high quality and efficient production of C. tinctorius.

From Stress to Success: Harnessing Technological Advancements to Overcome Climate Change Impacts in Citriculture

Climate change, primarily caused by human activities, leads to persistent alterations in Earth’s long-term weather patterns and temperatures, resulting in substantial regional climate disparities that significantly impact agricultural output. In the realm of sustainable citriculture, climate change poses a notable challenge by inducing abiotic stresses within citrus-producing regions. Projections suggest rising air temperatures by 2.2-5.1 °C, heightened instances of temperatures exceeding 30 °C during dry spells, freezing events, a reduction in rainfall by at least 4%, and amplified monsoonal precipitations. Such changes will inevitably affect citrus tree physiology and yield quality. The intricate connection between external climatic conditions and crucial physiological processes underscores the profound influence of climate change. Temperature fluctuations can disrupt leaf photosynthesis, stomatal conductance, flower and fruit development, fruit sugar production, coloration, abscission, carbohydrate accumulation, and ultimate fruit yield. This comprehensive review delves into the specific repercussions of climate change on citrus cultivation, focusing on variables like temperature variations, water availability, light intensity, atmospheric CO2 concentration, and salinity stress. Our exploration elucidates the adverse impact of these stressors on citrus crops, while highlighting innovative tactics and emerging technologies, including advanced monitoring systems, precision irrigation, automated climate regulation, molecular priming through biostimulants, shade netting, and particle film technologies. By mitigating the adverse effects of environmental stressors, these strategies empower citrus growers to navigate challenges like excessive solar radiation, temperature fluctuations, soil moisture management, erosion prevention, and enhanced soil quality. These combined efforts forge a path toward a more resilient citriculture capable of effectively countering the abiotic stresses stemming from climate change.

Sensitivity of physiological traits to different short-term drought events and subsequent recovery at the sapling stage in European white elm (Ulmus laevis Pall.)

There is an urgent need to better understand the processes underlying trees resistance and resilience to drought as a prerequisite for adapting to climate change. In this study, the effect of different short-term drought events on the physiology of European white elm saplings, as well as the rates at which their physiological traits recover after drought were identified. Elm saplings responded sensitively to drought stress: leaf water potential, net photosynthesis and stomatal conductance were the most sensitive traits. The normalized difference vegetation index and leaf water content responded only to severe drought stress conditions. Drought triggered the conversion of soluble carbohydrates to starch in leaves but not in roots. Root function was severely damaged by drought as indicated by increased root electrolyte leakage. Tree survival and the recovery rate were significantly better under two shorter drought periods compared to one longer drought. For this reason, the precipitation pattern in models evaluating tree survival under climatic change has to be taken into account. The differences in the studied traits between surviving and dying saplings increased as drought progressed and leaf water content together with leaf reflectance indexes were identified as the best indicators for evaluating tree mortality risk. These findings are very important, as they show that these specific traits can be used to identify trees susceptible to drought in the field as they can be sensed remotely.

Estimating canopy stomatal conductance and photosynthesis in apple trees by upscaling parameters from the leaf scale to the canopy scale in Jinzhong Basin on Loess Plateau

The estimations of stomatal conductance and photosynthesis performed by upscaling the parameters from the leaf scale to the canopy scale are key points in the fields of forest ecohydrology and physiology. The foundation for solving this scientific problem is determining the optimal models for calculating the leaf stomatal conductance (gl) and photosynthetic rate (Pl). In this study, we used the Jarvis model combined with modification factors, including leaf–air temperature (ΔT) and CO2 concentration inside and outside the stomata (ΔC), to estimate gl and the new Ye light–response model to estimate the Pl of apple trees in Jinzhong Basin on Loess Plateau. The results show that the modified Jarvis (JarvisΔT-ΔC) model and the new Ye light–response model could estimate gl and Pl, respectively, with very high accuracy, with R2 values of 0.926 and 0.959 for the former, and 0.987 and 0.983 for the latter in 2019 and 2021, respectively. Then, we estimated the canopy stomatal conductance (gc) and photosynthetic rate (Pc) by first dividing the apple tree canopy into sunlit and shaded leaves and then summing the contribution of sunlit and shaded gl, Pl and leaf area index. Our efforts will be a valid reference for estimating the gc and Pc of other tree or crop species in the future.

Effects of Light Intensity and Water Stress on Growth, Photosynthetic Characteristics and Plant Survival of Cistus heterophyllus Desf. Subsp. carthaginensis (Pau) M. B. Crespo & Mateo

The objective of this study was to identify the physiological mechanisms used by Cistus heterophyllus Desf. Subsp. carthaginensis (Pau) M. B. Crespo & Mateo, a species in critical danger of extinction, to cope with two typical abiotic conditions. During the summer of 2021, plants were cultivated under a shade mesh that intercepted 50% of the incident solar radiation (SHADE) and in natural conditions (SUN). Three irrigation treatments were also applied: control, T1, moderate water deficit; T2, 60% of the control, severe deficit; and T3, 30% of the control. Therefore, there were six treatments (SUN-T1, SUN-T2, SUN-T3, SHADE-T1, SHADE-T2, SHADE-T3). Plants were more affected by solar radiation than by deficit irrigation. Although leaf water potential, stomatal conductance and root biomass decreased by up to 45%, 63% and 65%, respectively, as deficit irrigation increased, plants were able to develop a leaf osmotic adjustment and an improved intrinsic water-use efficiency to maintain their growth and survival rate. Shade conditions improved gas exchange, reduced leaf temperature and induced the synthesis of chlorophylls, regardless of the irrigation level imposed. This indicated that radiation was the most limiting factor in our experiment. Applying 50% of the radiation and a moderate water deficit would help to obtain a good plant development and high survival rate in future recovery and conservation programs for the species.

Insights into physiological and metabolic modulations instigated by exogenous sodium nitroprusside and spermidine reveals drought tolerance in Helianthus annuus L.

Drought is the most critical climatic factor instigating severe threats to crop production worldwide. As stress ameliorants, exogenous sodium nitroprusside (SNP) or spermidine (Spd) supply has positive responses in alleviating the drought adversities in crops, however, reports regarding their combined effects is still elusive. Here, the protective role of SNP and Spd to confer drought resistance in sunflower (Helianthus annuus L.) through up-regulation of physiological and metabolic processes was investigated. Plants were foliar sprayed with individual or combined SNP (100 μM) or Spd (100 μM). Drought was induced by keeping the soil at 100% (normal) and 60% (drought stress) field capacity levels. Drought exposure caused a marked decline in relative water content (RWC), excised leaf water retention (ELWR), net photosynthesis (PN), transpiration rate (E), stomatal conductance (gs), and sub-stomatal conductance (Ci) with substantial increase in catalase (CAT), superoxide dismutase (SOD), and peroxidase (POX). SNP plus Spd exhibited a considerable increase in CAT, SOD, and POX activities under drought, and helped the plants to retain optimum water status and gas exchange attributes. Similarly, hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents were increased significantly to drought; however, a notable decline was recorded in drought prone plants treated with exogenous SNP plus Spd. Moreover, addition of SNP plus Spd under drought caused a remarkable increase in chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll total (Chl t), carotenoids (Car), and growth traits like shoot length (SL), root length (RL), shoot fresh weight (SFW), shoot dry weight (SDW), root dry weight (RDW). Combined SNP and Spd application could potentially alleviate the drought-induced damages in sunflower through increased water status (8–10%), antioxidant enzymes (17–28%), chlorophyll pigments (14–21%), and growth performance (12–22%) under drought stress.

Impact of soil moisture stress during the silk emergence and grain-filling in maize.

Suboptimal soil moisture during the growing season often limits maize growth and yield. However, the growth stage-specific responses of maize to soil moisture regimes have not been thoroughly investigated. This study investigated the response of maize to five different soil moisture regimes, that are, 0.25, 0.20, 0.15, 0.10, and 0.05 m3 m-3 volumetric water content (VWC), during flowering and grain-filling stages. Sub-optimal soil moisture at the flowering and grain-filling stages reduced ear leaf stomatal conductance by 73 and 64%, respectively. An increase in stress severity caused significant reductions in ear leaf chlorophyll content and greenness-associated vegetation indices across growth stages. Fourteen days of soil moisture stress during flowering delayed silk emergence, reduced silk length (19%), and silk fresh weight (34%). Furthermore, sub-optimal soil moisture caused a significant reduction in both kernel number (53%) and weight (54%). Soil moisture stress at the flowering had a direct impact on kernel number and an indirect effect on kernel weight. During grain-filling, disruption of ear leaf physiology resulted in a 34% decrease in kernel weight and a 43% decrease in kernel number. Unlike grain-filling, treatments at the flowering significantly reduced kernel starch (3%) and increased protein by 29%. These findings suggest that developing reproductive stage stress-tolerant hybrids with improved resilience to soil moisture stress could help reduce the yield gap between irrigated and rainfed maize.