Insights on physiological, antioxidant and flowering response to salinity stress of two candidate ornamental species: the native coastal geophytes Pancratium maritimum L. and Eryngium maritimum L.

Increasing seawater influence in coastal areas is an ongoing environmental issue. Gardening is a widespread activity mainly in touristic areas such as the Mediterranean coasts. However, the use of exotic species well adapted to salinity encompasses the risk of invasive species introduction. This study aimed to evaluate salinity tolerance of native geophytes, Pancratium maritimum L. and Eryngium maritimum L., to assess their use as ornamental species in salt affected coastal areas. Experiments were conducted using cultivated plants for flowering response and physiological and enzymatic antioxidant response. Six treatments were applied for two months, exposing plants to seawater (SW) dilutions (Tap-Water, 6.25%SW, 12.5%SW, 25%SW, 50%SW and 100%SW). Taxa decreased inflorescence production being this effect more architectonical in E. maritimum and affecting all inflorescence integrity in P. maritimum. Flowering time was strongly delayed and reduced in P. maritimum, while E. maritimum showed smaller effects among treatments. Physiological and biochemical response showed at moderate salinity levels (1/4SW) variation concomitant with late stress response and senescence in P. maritimum, with decreased water use efficiency, NPQ values, and enzymatic activity, and increased malondialdehyde (MDA) levels. In contrast, E. maritimum showed early stress response with steady gas exchange response, increasing NPQ values and catalase (CAT) and superoxide dimutase (SOD) activity, and decreasing MDA levels with salinity. Glutathione enzymes showed limited participation in both species. The results of this study suggest that neither species can be classified as halophytes, but they exhibit tolerance to low and moderate salinity levels, making them suitable for ornamental use. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-024-01502-0.

Heart Rate and Its Variability Are Associated With Resting Metabolic Rate and Substrate Oxidation in Young Women but Not in Men.

BACKGROUND: This study aims to examine the relationship between resting vagal-related heart rate variability (HRV) parameters and heart rate (HR) with resting metabolic rate (RMR) and respiratory exchange ratio (RER) in young adults. METHODS: A total of 74 young adults (22 ± 2 years old, 51 women) were included in this cross-sectional study. HRV was assessed using a HR monitor, whereas RMR and RER were determined by indirect calorimetry. RESULTS: Linear regression analyses showed a positive association between HR and RER in women (standardized ß = 0.384, p = 0.008), while negative associations were observed between vagal-related HRV parameters and RER in women (ß ranged from -0.262 to -0.254, all p ≤ 0.042). No significant association was found between the abovementioned physiological parameters in men. CONCLUSION: Here, we show that HR is positively associated with RER in young women but not in men, while vagal-related HRV parameters are inversely related to RMR, therefore suggesting a potential sexual dimorphism between cardiac rhythm and its relationship with markers of cardiometabolic health status. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02365129.

NaCl-induced effects on photosynthesis, ion relations, and growth of Chloris gayana Kunth in the presence of two levels of KCl.

Soil salinization is a widespread environmental problem that impacts agriculture. Potassium fertilization is often associated with stress mitigation. Aiming to identify the ability of Rhodes grass (Chloris gayana Kunth) to cope with high salt as well as to investigate the potential of K+ fertilization to alleviate stress symptoms, we investigated the combined effects of NaCl and KCl on photosynthesis, ion distribution, and growth of two Rhodes grass cultivars, Callide and Reclaimer. Plants were grown under different regimes (0, 200, 400, and 600 mM NaCl + 1 or 10 mM KCl). For Reclaimer, 10 mM KCl induced positive effects in photochemistry under 0 and 200 mM NaCl, as illustrated by fluorescence transients OJIP-bands and JIP-test parameters. However, such improvements did not lead to superior biomass accumulation nor net photosynthesis compared to the corresponding treatments under 1 mM KCl, which may not justify KCl application. In Callide 10 mM KCl induced deleterious effects on photochemistry of plants under low NaCl levels. High salinity (600 mM) induced stress-triggered biomass reduction of up to 70% in both cultivars, but all plants remained photosynthetically active. Exposure of both cultivars to NaCl concentrations equal to or higher than 200 mM triggered response mechanisms such as the ability to accumulate inorganic solutes accounting to osmotic potential, stomata closure, and excretion (up to 70%) of the retained Na+ onto the leaf surface irrespective of KCl. Our data reinforce that Rhodes grass is an auspicious forage crop for saline environments and, therefore, in revegetation programs for saline soils pasture in subtropical regions.

Aphid Colonisation's Impact on Photosynthetic and CHN Traits in Three Ornamental Shrubs.

Shrubs are a significant component of urban vegetation found in parks, but they experience various influences from biotic and abiotic agents, among which aphids play an important role. In this work, the effects of aphid colonisation on three shrub species in urban environments were examined. Fourteen parameters were analysed, describing the photosynthetic pigment content and gas exchange to carbon, nitrogen, and hydrogen partitions. While no significant effect of colonisation was found on photosynthetic pigment parameters, the effect was significant on gas exchange parameters. The strongest effect of aphid colonisation achieved was on nitrogen partition and the C/N ratio, parameters that could be suggested for further similar studies. All parameters were classified into two groups according to their principal component analysis, suggesting a correlation between nitrogen and carbon content, the C/N ratio, measured gas exchange parameters, and chlorophyll a content. The ratio between net photosynthesis and dark respiration (A/K) was classified in the second group, suggesting that this parameter provides additional information on the effect of aphid colonisation and deserves special attention in further studies. There were differences in the effect of aphid colonisation on the physiology of the examined shrub species, especially in cases where a decrease in the C/N ratio was achieved in Spirea trilobata and Cydonia japonica, while an increase in the same parameter was recorded in Hybiscus syriacus.

The Potential of Helichsryum splendidum (Thunb.) Less. for the Restoration of Sites Polluted with Coal Fly Ash.

The disposal of coal fly ash (CFA) generated from coal-fired power stations has serious impact on the ecosystem, by converting large pieces of land to barren ash dams with the potential to contaminate groundwater, surface water, air and soil. The aim of this study was to clarify the potential of phytoremediation using Helichrysum splendidum (Thunb.) Less. in areas polluted by CFA through conduction of pot trial experiments for 14 weeks. Plants of the same age were cultivated in CFA to assess their growth, photosynthetic rate and tolerance towards metal toxicity. This study revealed that the CFA was moderately polluted with heavy metals, and a lower photosynthetic rate was recorded for the CFA plants in comparison to the controls (plants grown in soil). Although the CO2 assimilation rate was lower for the CFA plants, increased growth was recorded for all the plants tested. Inductively coupled plasma mass spectrometry (ICP-MS) was used to quantify the amount of trace elements in samples and parameters including translocation factor (TF) and bioconcentration factor (BCF) were used to evaluate the phytoremediation potential of H. splendidum (Thunb.) Less. The results revealed that higher concentrations of Cd, Co, Cr, Cu, Mn and Pb were accumulated in the roots, while As, Ni and Zn were found in the shoots. Elements including As, Cr and Zn reported TF values above 1, indicating the plants' phytoextraction potential. The BCF values for As, Cu and Zn were 1.22, 1.19 and 1.03, indicating effectiveness in the phytostabilization processes. A removal rate efficiency ranging from 18.0 to 56.7% was recorded confirming that, H. splendidum (Thunb.) Less. can be employed for restoration of CFA dams.

Compressed sensing reconstruction for high-SNR, rapid dissolved 129Xe gas exchange MRI.

PURPOSE: Three-dimensional hyperpolarized 129Xe gas exchange imaging suffers from low SNR and long breath-holds, which could be improved using compressed sensing (CS). The purpose of this work was to assess whether gas exchange ratio maps are quantitatively preserved in CS-accelerated dissolved-phase 129Xe imaging and to investigate the feasibility of CS-dissolved 129Xe imaging with reduced-cost natural abundance (NA) xenon. METHODS: 129Xe gas exchange imaging was performed at 1.5 T with a multi-echo spectroscopic imaging sequence. A CS reconstruction with an acceleration factor of 2 was compared retrospectively with conventional gridding reconstruction in a cohort of 16 healthy volunteers, 5 chronic obstructive pulmonary disease patients, and 23 patients who were hospitalized following COVID-19 infection. Metrics of comparison included normalized mean absolute error, mean gas exchange ratio, and red blood cell (RBC) image SNR. Dissolved 129Xe CS imaging with NA xenon was assessed in 4 healthy volunteers. RESULTS: CS reconstruction enabled acquisition time to be halved, and it reduced background noise. Median RBC SNR increased from 6 (2-18) to 11 (2-100) with CS, and there was strong agreement between CS and gridding mean ratio map values (R2 = 0.99). Image fidelity was maintained for gridding RBC SNR > 5, but below this, normalized mean absolute error increased nonlinearly with decreasing SNR. CS increased the mean SNR of NA 129Xe images 3-fold. CONCLUSION: CS reconstruction of dissolved 129Xe imaging improved image quality with decreased scan time, while preserving key gas exchange metrics. This will benefit patients with breathlessness and/or low gas transfer and shows promise for NA-dissolved 129Xe imaging.

Shorting the metaphorical circuit: vascular partitioning and stomatal patchiness can create apparent unsaturation and CO2 gradient inversion in the Ohmic analogy for leaf gas exchange.

Analyses of leaf gas exchange rely on an Ohmic analogy that arrays single stomatal, internal air space, and mesophyll conductances in series. Such models underlie inferences of mesophyll conductance and the relative humidity of leaf airspaces, reported to fall as low as 80%. An unresolved question is whether such series models are biased with respect to real leaves, whose internal air spaces are chambered at various scales by vasculature. To test whether unsaturation could emerge from modeling artifacts, we compared series model estimates with true parameter values for a chambered leaf with varying distributions and magnitudes of leaf surface conductance ('patchiness'). Distributions of surface conductance can create large biases in gas exchange calculations. Both apparent unsaturation and internal CO2 gradient inversion can be produced by the evolution of broader distributions of stomatal apertures consistent with a decrease in surface conductance, as might occur under increasing vapor pressure deficit. In gas exchange experiments, the behaviors of derived quantities defined by simple series models are highly sensitive to the true partitioning of flux and stomatal apertures across leaf surfaces. New methods are needed to disentangle model artifacts from real biological responses.

Biochar improves growth and physiology of Swietenia macrophylla king in contaminated soil by copper.

The production of açaí seed waste from the commercial and extractive exploitation of the Euterpe oleraceae palm tree is a serious problem that contributes to environmental contamination and production of greenhouse gases, a fact that suggests the need for an environmentally correct destination for this waste produced on a large scale. To this end, this study was conducted to evaluate the potential of acaí seed biochar (BCA) in mitigating the toxic effects of copper in Brazilian mahogany plants, analyzing biometrics and gas exchange. The experimental design was in randomized blocks, with five blocks, in a 4 × 3 factorial scheme, corresponding to the control (without Cu) and three concentration of Cu (200, 400, and 600 mg Cu kg-1) and three levels of BCA (0%, 5% and 10%) proportional to the amount of soil in the pots, totaling sixty experimental units. The use of 5% BCA in soils contaminated with up to 200 mg kg-1 Cu promoted biometric increase (height, diameter, number of leaves), maintaining gas exchange (photosynthesis, stomatal conductance, transpiration, internal carbon and internal/external carbon), and consequently, maintaining water use efficiency in plants under abiotic stress, resulting in plant growth. The findings of this study allow us to indicate the use of biochar in remediating and improving the growth of plants grown in copper-contaminated soils. The production of biochar from açaí seeds is an ecologically sustainable alternative, because it reduces its accumulation on public roads and contributes to reducing soil pollution. In the context of public policies, biochar production could be a source of income in the context of the bioeconomy and circular economy practiced in the Amazon, because it is produced in large quantities.

Effect of CO2 Elevation on Tomato Gas Exchange, Root Morphology and Water Use Efficiency under Two N-Fertigation Levels.

Atmospheric elevated CO2 concentration (e[CO2]) decreases plant nitrogen (N) concentration while increasing water use efficiency (WUE), fertigation increases crop nutrition and WUE in crop; yet the interactive effects of e[CO2] coupled with two N-fertigation levels during deficit irrigation on plant gas exchange, root morphology and WUE remain largely elusive. The objective of this study was to explore the physiological and growth responses of ambient [CO2] (a[CO2], 400 ppm) and e[CO2] (800 ppm) tomato plant exposed to two N-fertigation regimes: (1) full irrigation during N-fertigation (FIN); (2) deficit irrigation during N-fertigation (DIN) under two N fertilizer levels (reduced N (N1, 0.5 g pot-1) and adequate N (N2, 1.0 g pot-1). The results indicated that e[CO2] associated with DIN regime induced the lower N2 plant water use (7.28 L plant-1), maintained leaf water potential (-5.07 MPa) and hydraulic conductivity (0.49 mol m-2 s-1 MPa-1), greater tomato growth in terms of leaf area (7152.75 cm2), specific leaf area (223.61 cm2 g-1), stem and total dry matter (19.54 g and 55.48 g). Specific root length and specific root surface area were increased under N1 fertilization, and root tissue density was promoted in both e[CO2] and DIN environments. Moreover, a smaller and denser leaf stomata (4.96 µm2 and 5.37 mm-2) of N1 plant was obtained at e[CO2] integrated with DIN strategy. Meanwhile, this combination would simultaneously reduce stomatal conductance (0.13 mol m-2 s-1) and transpiration rate (1.91 mmol m-2 s-1), enhance leaf ABA concentration (133.05 ng g-1 FW), contributing to an improvement in WUE from stomatal to whole-plant scale under each N level, especially for applying N1 fertilization (125.95 µmol mol-1, 8.41 µmol mmol-1 and 7.15 g L-1). These findings provide valuable information to optimize water and nitrogen fertilizer management and improve plant water use efficiency, responding to the potential resource-limited and CO2-enriched scenario.

Variable positive end-expiratory pressure in an experimental model of acute respiratory distress syndrome: an advanced ventilation modality.

Background: Introducing variability in tidal volume, ventilatory frequency, or both is beneficial during mechanical ventilation in acute respiratory distress syndrome (ARDS). We investigated whether applying cycle-by-cycle variability in the positive end-expiratory pressure (PEEP) exerts beneficial effect on lung function in a model of ARDS. Methods: Rabbits with lung injury were randomly allocated to receive mechanical ventilation for 6 h by applying a pressure-controlled mode with constant PEEP of 7 cm H2O (PC group: n=6) or variable PEEP (VEEP) with a coefficient of variation of 21.4%, range 4-10 cm H2O (PC-VEEP group; n=6). Lung oxygenation index (Pao2/FiO2) after 6 h of ventilation (H6) was the primary outcome and respiratory mechanics, lung volume, intrapulmonary shunt, and lung inflammatory markers were secondary outcomes. Results: After lung injury, both groups presented moderate-to-severe ARDS (Pao2/FiO2 <27 kPa). The Pao2/FiO2 was significantly higher in the PC-VEEP group than in the PC group at H6 (12.3 [sd 3.5] vs 19.2 [7.2] kPa, P=0.013) and a lower arterial partial pressure of CO2 at 1-3 h (P<0.02). The ventilation-induced increases in airway resistance and tissue elastance were prevented by PC-VEEP. There was no evidence for a difference in minute volume, driving pressure, end-tidal CO2, lung volumes, intrapulmonary shunt fraction, and cytokines between the ventilation modes. Conclusions: Prolonged mechanical ventilation with cycle-by-cycle VEEP prevents deterioration in gas exchange and respiratory mechanics in a model of ARDS, suggesting the benefit of this novel ventilation strategy to optimise gas exchange without increasing driving pressure and lung overdistension.

Piriformospora indica alleviates soda saline-alkaline stress in Glycine max by modulating plant metabolism.

Soil salinization is one of the major factors limiting agricultural production. Utilizing beneficial microorganisms like Piriformospora indica (P. indica) to enhance plant tolerance to abiotic stresses is a highly effective method, but the influence of P. indica on the growth of soybean in natural saline-alkaline soil remains unclear. Therefore, we investigated the effects of non-inoculation, P. indica inoculation, and fertilization on the growth, antioxidant defense, osmotic adjustment, and photosynthetic gas exchange parameters of soybean under two different levels of saline-alkaline stress in non-sterilized natural saline-alkaline soil. The study found that: 1) P. indica inoculation significantly promoted soybean growth, increasing plant height, root length, and biomass. Under mildly saline-alkaline stress, the increases were 11.5%, 16.0%, and 14.8%, respectively, compared to non-inoculated treatment. Under higher stress, P. indica inoculation achieved the same level of biomass increase as fertilization, while fertilization only significantly improved stem diameter. 2) Under saline-alkaline stress, P. indica inoculation significantly increased antioxidant enzyme activities and reduced malondialdehyde (MDA) content. Under mildly stress, MDA content was reduced by 47.1% and 43.3% compared to non-inoculated and fertilized treatments, respectively. Under moderate stress, the MDA content in the inoculated group was reduced by 29.9% and 36.6% compared to non-inoculated and fertilized treatments, respectively. Fertilization only had a positive effect on peroxidase (POD) activity. 3) P. indica inoculation induced plants to produce more osmotic adjustment substances. Under mildly stress, proline, soluble sugars, and soluble proteins were increased by 345.7%, 104.4%, and 6.9%, respectively, compared to non-inoculated treatment. Under higher stress, the increases were 75.4%, 179.7%, and 12.6%, respectively. Fertilization had no significant positive effect on proline content. 4) With increasing stress, soybean photosynthetic capacity in the P. indica-inoculated treatment was significantly higher than in the non-inoculated treatment, with net photosynthetic rate increased by 14.8% and 37.0% under different stress levels. These results indicate that P. indica can enhance soybean's adaptive ability to saline-alkaline stress by regulating ROS scavenging capacity, osmotic adjustment substance content, and photosynthetic capacity, thereby promoting plant growth. This suggests that P. indica has great potential in improving soybean productivity in natural saline-alkaline soils.

Invasive ventilation at the boundary of viability: A respiratory pathophysiology study of infants born between 22 and 24 weeks of gestation.

BACKGROUND: Invasive ventilation of infants born before 24 weeks of gestation is critical for survival and long-term respiratory outcomes, but currently there is a lack of evidence to guide respiratory management. We aimed to compare respiratory mechanics and gas exchange in ventilated extremely preterm infants born before and after 24 weeks of gestation. METHODS: Secondary analysis of two prospective observational cohort studies, comparing respiratory mechanics and indices of gas exchange in ventilated infants born at 22-24 weeks of gestation (N=14) compared to infants born at 25-27 weeks (N=37). The ventilation/perfusion ratio (VA/Q), intrapulmonary shunt, alveolar dead space (VDalv) and adjusted alveolar surface area (SA) were measured in infants born at the Neonatal Unit of King's College Hospital NHS Foundation Trust, London, UK. RESULTS: Compared to infants of 25-27 weeks, infants of 22-24 weeks had higher median (IQR) intrapulmonary shunt [18 (4 - 29) % vs 8 (2 - 12) %, p=0.044] and higher VDalv [0.9 (0.6 - 1.4) vs 0.6 (0.5 - 0.7) ml/kg, p=0.036], but did not differ in VA/Q. Compared to infants of 25-27 weeks, the infants of 22-24 weeks had a lower adjusted SA [509 (322- 687) vs 706 (564 - 800) cm2, p=0.044]. The infants in the two groups did not differ in any of the indices of respiratory mechanics. CONCLUSION: Ventilated infants born before 24 completed weeks of gestation exhibit abnormal gas exchange, with higher alveolar dead space and intrapulmonary shunt and a decreased alveolar surface area compared to extreme preterms born after 24 weeks of gestation.

The UCI Fluxtron: A versatile dynamic chamber and software system for biosphere-atmosphere exchange research.

Here we present the UCI Fluxtron, a cost-effective multi-enclosure dynamic gas exchange system that provides an adequate level of control of the experimental conditions for investigating biosphere-atmosphere exchange of trace gases. We focus on the hardware and software used to monitor, control, and record the air flows, temperatures, and valve switching, and on the software that processes the collected data to calculate the exchange flux of trace gases. We provide the detailed list of commercial materials used and also the software code developed for the Fluxtron, so that similar dynamic enclosure systems can be quickly adopted by interested researchers. Furthermore, the two software components -Fluxtron Control and Fluxtron Process- work independently of each other, thus being highly adaptable for other experimental designs. Beyond plants, the same experimental setup can be applied to the study of trace gas exchange by animals, microbes, soil, or any materials that can be enclosed in a suitable container.

Hepatopulmonary Syndrome: A Comprehensive Review.

Hepatopulmonary syndrome (HPS) is defined by abnormally dilated blood vessels and shunts within the lungs, leading to impaired oxygen exchange. This condition results from intricate interactions between the liver, the gastrointestinal system, and the lungs. This complex system primarily affects pulmonary endothelial, immunomodulatory, and respiratory epithelial cells. Consequently, this contributes to pathological pulmonary changes characteristic of HPS. A classification system based on the severity of oxygen deficiency has been proposed for grading the physiological dysfunction of HPS. Contrast-enhanced echocardiography is considered the primary radiological evaluation for identifying abnormal blood vessel dilations within the lungs, which, combined with an elevated alveolar-arterial gradient, is essential for making the diagnosis. Liver transplantation is the sole effective definitive treatment that can reverse the course of the condition. Despite often being symptomless, HPS carries a significant risk of mortality before transplantation, regardless of the severity of liver disease. Meanwhile, there is varying data regarding survival rates following liver transplantation. The adoption of the model for end-stage liver disease (MELD) standard exception policy has notably improved the results for individuals with HPS compared to the period before MELD was introduced. This review offers a summary of the present understanding, highlighting recent advancements in the diagnosis and treatment of HPS. Furthermore, it aims to augment comprehension of the condition's fundamental mechanisms through insights derived from experimental models and translational research.

Physiological trait coordination and variability across and within three Pinus species.

Studies have explored how traits separate plants ecologically and the trade-offs that underpin this separation. However, uncertainty remains as to the taxonomic scale at which traits can predictably separate species. We studied how physiological traits separated three Pinus (Pinus banksiana, Pinus resinosa, and Pinus strobus) species across three sites. We collected traits from four common leaf and branch measurements (light-response curves, CO2-response curves, pressure-volume curves, and hydraulic vulnerability curves) across each species and site. While common, these measurements are not typically measured together due to logistical constraints. Few traits varied across species and sites as expected given the ecological preferences of the species and environmental site characteristics. Some trait trade-offs present at broad taxonomic scales were observed across the three species, but most were absent within species. Certain trade-offs contrasted expectations observed at broader scales but followed expectations given the species' ecological preferences. We emphasize the need to both clarify why certain traits are being studied, as variation in unexpected but ecologically meaningful ways often occurs and certain traits might not vary substantially within a given lineage (e.g. hydraulic vulnerability in Pinus), highlighting the role a trait selection in trait ecology.

A Novel Method for Determining Ventilatory and Gas Exchange Dynamics During Exercise: The "Chirp" Waveform.

Quantitating exercise ventilatory and gas exchange dynamics affords insights into physiological control processes and cardiopulmonary dysfunction. We designed a novel waveform, the chirp waveform, to efficiently extract moderate intensity exercise response dynamics. In the chirp waveform, work rate fluctuates sinusoidally with constant amplitude as sinusoidal period decreases progressively from approximately 8.5 to 1.4 minutes over 30 minutes of cycle ergometry. We hypothesized that response dynamics of pulmonary ventilation (V̇E) and gas exchange (V̇O2 and V̇CO2) extracted from chirp waveform are similar to those obtained from step-wise transitions. Thirty-one participants (14 young-healthy, 7 older-healthy, 10 COPD patients) exercised on three occasions. Participants first performed ramp-incremental exercise for gas exchange threshold (GET) determination. In randomized order, the next two visits involved either chirp or step-wise waveforms. Work rate amplitude (20W to ∼95% GET work rate) and exercise duration (30 min) were the same for both waveforms. A first-order linear transfer function with system gain (G) and time constant (τ) characterized response dynamics. Agreement between model parameters extracted from chirp and step-wise waveforms was established using Bland-Altman analysis and Rothery's Concordance Coefficient (RCC). V̇E, V̇O2, and V̇CO2 Gs showed no systematic bias (p>0.178) and moderate-to-good agreement (RCC>0.772, p<0.01) between waveforms. Similarly, no systematic bias (p=0.815) and good agreement (RCC=0.837, p<0.001) was found for τV̇O2. Despite moderate agreement for τV̇CO2 (RCC=0.794, p<0.001) and τV̇E (RCC=0.722, p=0.083), chirp τ was less (-6.9(11.7)s and -12.2(22.5)s, respectively). We conclude that the chirp waveform is a promising method for measuring exercise response dynamics and investigating physiological control mechanisms.

Rewatering after drought: Unravelling the drought thresholds and function recovery-limiting factors in maize leaves.

Drought and subsequent rewatering are common in agriculture, where recovery from mild droughts is easier than from severe ones. The specific drought threshold and factors limiting recovery are under-researched. This study subjected maize plants to varying drought degrees before rewatering, and measuring plant water status, gas exchange, hydraulic conductance, hormone levels, and cellular damage throughout. We discovered that stomatal reopening in plants was inhibited with leaf water potentials below about -1.7 MPa, hindering postdrought photosynthetic recovery. Neither hydraulic loss nor abscisic acid (ABA) content was the factor inhibited stomatal reopening on the second day following moderate drought stress and rewatering. But stomatal reopening was significantly correlated to the interaction between hydraulic signals and ABA content under severe drought. Extended drought led to leaf death at about -2.8 MPa or 57% relative water content, influenced by reduced rehydration capacity, not hydraulic failure. The lethal threshold remained relatively constant across leaf stages, but the recoverable safety margin (RSM), that is, the water potential difference between stomatal closure and recovery capacity loss, significantly decreased with leaf aging due to delayed stomatal closure during drought. Our findings indicate hydraulic failure alone does not cause maize leaf death, highlighting the importance of RSM in future research.

Nutrient strengthening and lead alleviation in Brassica Napus L. by foliar ZnO and TiO2-NPs modulating antioxidant system, improving photosynthetic efficiency and reducing lead uptake.

With the anticipated foliar application of nanoparticles (NPs) as a potential strategy to improve crop production and ameliorate heavy metal toxicity, it is crucial to evaluate the role of NPs in improving the nutrient content of plants under Lead (Pb) stress for achieving higher agriculture productivity to ensure food security. Herein, Brassica napus L. grown under Pb contaminated soil (300 mg/kg) was sprayed with different rates (0, 25, 50, and 100 mg/L) of TiO2 and ZnO-NPs. The plants were evaluated for growth attributes, photosynthetic pigments, leaf exchange attributes, oxidant and antioxidant enzyme activities. The results revealed that 100 mg/L NPs foliar application significantly augmented plant growth, photosynthetic pigments, and leaf gas exchange attributes. Furthermore, 100 mg/L TiO2 and ZnO-NPs application showed a maximum increase in SPAD values (79.1%, 68.9%). NPs foliar application (100 mg/L TiO2 and ZnO-NPs) also substantially reduced malondialdehyde (44.3%, 38.3%), hydrogen peroxide (59.9%, 53.1%), electrolyte leakage (74.8%, 68.3%), and increased peroxidase (93.8%, 89.1%), catalase (91.3%, 84.1%), superoxide dismutase (81.8%, 73.5%) and ascorbate peroxidase (78.5%, 73.7%) thereby reducing Pb accumulation. NPs foliar application (100 mg/L) significantly reduced root Pb (45.7%, 42.3%) and shoot Pb (84.1%, 76.7%) concentration in TiO2 and ZnO-NPs respectively, as compared to control. Importantly, macro and micronutrient analysis showed that foliar application 100 mg/L TiO2 and ZnO-NPs increased shoot zinc (58.4%, 78.7%) iron (79.3%, 89.9%), manganese (62.8%, 68.6%), magnesium (72.1%, 93.7%), calcium (58.2%, 69.9%) and potassium (81.5%, 68.6%) when compared to control without NPs. The same trend was observed for root nutrient concentration. In conclusion, we found that the TiO2 and ZnO-NPs have the greatest efficiency at 100 mg/L concentration to alleviate Pb induced toxicity on growth, photosynthesis, and nutrient content of Brassica napus L. NPs foliar application is a promising strategy to ensure sustainable agriculture and food safety under metal contamination.

Acclimation of mature spruce and beech to five years of repeated summer drought - The role of stomatal conductance and leaf area adjustment for water use.

Forests globally are experiencing severe droughts, leading to significant reductions in growth, crown dieback and even tree mortality. The ability of forest ecosystems to acclimate to prolonged and repeated droughts is critical for their survival with ongoing climate change. In a five-year throughfall exclusion experiment, we investigated the long-term physiological and morphological acclimation of mature Norway spruce (Picea abies [L.] KARST.) and European beech (Fagus sylvatica L.) to repeated summer drought at the leaf, shoot and whole tree level. Throughout the drought period, spruce reduced their total water use by 70 % to only 4-9 L per day and tree, while beech was less affected with about 30 % reduction of water use. During the first two summers, spruce achieved this by closing their stomata by up to 80 %. Additionally, from the second drought summer onwards, spruce produced shorter shoots and needles, resulting in a stepwise reduction of total leaf area of over 50 % by the end of the experiment. Surprisingly, no premature leaf loss was observed. This reduction in leaf area allowed a gradual increase in stomatal conductance. After the five-year drought experiment, water consumption per leaf area was the same as in the controls, while the total water consumption of spruce was still reduced. In contrast, beech showed no significant reduction in whole-tree leaf area, but nevertheless reduced water use by up to 50 % by stomatal closure. If the restriction of transpiration by stomatal closure is sufficient to ensure survival of Norway spruce during the first drought summers, then the slow but steady reduction in leaf area will ensure successful acclimation of water use, leading to reduced physiological drought stress and long-term survival. Neighboring beech appeared to benefit from the water-saving strategy of spruce by using the excess water.