High heat tolerance, evaporative cooling, and stomatal decoupling regulate canopy temperature and their safety margins in three European oak species.

Heatwaves and soil droughts are increasing in frequency and intensity, leading many tree species to exceed their thermal thresholds, and driving wide-scale forest mortality. Therefore, investigating heat tolerance and canopy temperature regulation mechanisms is essential to understanding and predicting tree vulnerability to hot droughts. We measured the diurnal and seasonal variation in leaf water potential (Ψ), gas exchange (photosynthesis Anet and stomatal conductance gs), canopy temperature (Tcan), and heat tolerance (leaf critical temperature Tcrit and thermal safety margins TSM, i.e., the difference between maximum Tcan and Tcrit) in three oak species in forests along a latitudinal gradient (Quercus petraea in Switzerland, Quercus ilex in France, and Quercus coccifera in Spain) throughout the growing season. Gas exchange and Ψ of all species were strongly reduced by increased air temperature (Tair) and soil drying, resulting in stomatal closure and inhibition of photosynthesis in Q. ilex and Q. coccifera when Tair surpassed 30°C and soil moisture dropped below 14%. Across all seasons, Tcan was mainly above Tair but increased strongly (up to 10°C > Tair) when Anet was null or negative. Although trees endured extreme Tair (up to 42°C), positive TSM were maintained during the growing season due to high Tcrit in all species (average Tcrit of 54.7°C) and possibly stomatal decoupling (i.e., Anet ≤0 while gs >0). Indeed, Q. ilex and Q. coccifera trees maintained low but positive gs (despite null Anet), decreasing Ψ passed embolism thresholds. This may have prevented Tcan from rising above Tcrit during extreme heat. Overall, our work highlighted that the mechanisms behind heat tolerance and leaf temperature regulation in oak trees include a combination of high evaporative cooling, large heat tolerance limits, and stomatal decoupling. These processes must be considered to accurately predict plant damages, survival, and mortality during extreme heatwaves.

Canola (Brassica napus) enhances sodium chloride and sodium ion tolerance by maintaining ion homeostasis, higher antioxidant enzyme activity and photosynthetic capacity fluorescence parameters.

Under salt stress, plants are forced to take up and accumulate large amounts of sodium (Na+ ) and chloride (Cl- ). Although most studies have focused on the toxic effects of Na+ on plants, Cl- stress is also very important. This study aimed to clarify physiological mechanisms underpinning growth contrasts in canola varieties with different salt tolerance. In hydroponic experiments, 150mM Na+ , Cl- and NaCl were applied to salt-tolerant and sensitive canola varieties. Both NaCl and Na+ treatments inhibited seedling growth. NaCl caused the strongest damage to both canola varieties, and stress damage was more severe at high concentrations of Na+ than Cl- . High Cl- promoted the uptake of ions (potassium K+ , calcium Ca2+ ) and induced antioxidant defence. Salt-tolerant varieties were able to mitigate ion toxicity by maintaining lower Na+ content in the root system for a short period of time, and elevating magnesium Mg2+ content, Mg2+ /Na+ ratio, and antioxidant enzyme activity to improve photosynthetic capacity. They subsequently re-established new K+ /Na+ and Ca2+ /Na+ balances to improve their salt tolerance. High concentrations of Cl salts caused less damage to seedlings than NaCl and Na salts, and Cl- also had a positive role in inducing oxidative stress and responsive antioxidant defence in the short term.

Differential response of proline metabolism defense, Na+ absorption and deposition to salt stress in salt-tolerant and salt-sensitive rapeseed (Brassica napus L.) genotypes.

Soil salinization is a major abiotic factor threatening rapeseed yields and quality worldwide, yet the adaptive mechanisms underlying salt resistance in rapeseed are not clear. Therefore, this study aimed to explore the differences in growth potential, sodium (Na+) retention in different plant tissues, and transport patterns between salt-tolerant (HY9) and salt-sensitive (XY15) rapeseed genotypes, which cultivated in Hoagland's nutrient solution in either the with or without of 150 mM NaCl stress. The results showed that the inhibition of growth-related parameters of the XY15 genotype was higher than those of the HY9 in response to salt stress. The XY15 had lower photosynthesis, chloroplast disintegration, and pigment content but higher oxidative damage than the HY9. Under NaCl treatment, the proline content in the root of HY9 variety increased by 8.47-fold, surpassing XY15 (5.41-fold). Under salt stress, the HY9 maintained lower Na+ content, while higher K+ content and exhibited a relatively abundant K+/Na+ ratio in root and leaf. HY9 also had lower Na+ absorption, Na+ concentration in xylem sap, and Na+ transfer factor than XY15. Moreover, more Na+ contents were accumulated in the root cell wall of HY9 with higher pectin content and pectin methylesterase (PME) activity than XY15. Collectively, our results showed that salt-tolerant varieties absorbed lower Na+ and retained more Na+ in the root cell wall (carboxyl group in pectin) to avoid leaf salt toxicity and induced higher proline accumulation as a defense and antioxidant system, resulting in higher resistance to salt stress, which provides the theoretical basis for screening salt resistant cultivars.

FeONPs alleviate cadmium toxicity in Solanum melongena through improved morpho-anatomical and physiological attributes, along with oxidative stress and antioxidant defense regulations.

In this study, various constraints of Cd toxicity on growth, morpho-anatomical characters along with physiological and biochemical metabolic processes of Solanum melongena L. plants were analyzed. Conversely, ameliorative role of iron oxide nanoparticles (FeONPs) was examined against Cd stress. For this purpose, the following treatments were applied in completely randomized fashion; 3 mM CdCl2 solution applied with irrigation water, 40 and 80 ppm solutions of FeONPs applied via foliar spray. Regarding the results, Cd caused oxidative damage to plants' photosynthetic machinery, resulting in elevated levels of stress-markers like malondialdehyde (MDA), hydrogen peroxide (H2O2), and electrolytic leakage (EL) along with slight increase in antioxidants activities, including glutathione (GsH), ascorbate (AsA), catalases (CAT), peroxidases (POD), superoxide dismutase (SOD), and ascorbate peroxidases (APX). Also, high Cd level in plants disturb ions homeostasis and reduced essential minerals uptake, including Ca and K. This ultimately reduced growth and development of S. melongena plants. In contrast, FeONPs supplementations improved antioxidants (enzymatic and non-enzymatic) defenses which in turn limited ROS generation and lowered the oxidative damage to photosynthetic machinery. Furthermore, it maintained ionic balance resulting in enhanced uptake of Ca and K nutrients which are necessary for photosynthesis, hence also improved photosynthesis rate of S. melongena plants. Overall, FeONPs foliar spray effectively mitigated Cd toxicity imposed on S. melongena plants.

Cytokinin oxidase2-deficient mutants improve panicle and grain architecture through cytokinin accumulation and enhance drought tolerance in indica rice.

KEY MESSAGE: The Osckx2 mutant accumulates cytokinin thereby enhancing panicle branching, grain yield, and drought tolerance, marked by improved survival rate, membrane integrity, and photosynthetic function. Cytokinins (CKs) are multifaceted hormones that regulate growth, development, and stress responses in plants. Cytokinins have been implicated in improved panicle architecture and grain yield; however, they are inactivated by the enzyme cytokinin oxidase (CKX). In this study, we developed a cytokinin oxidase 2 (Osckx2)-deficient mutant using CRISPR/Cas9 gene editing in indica rice and assessed its function under water-deficit and salinity conditions. Loss of OsCKX2 function increased grain number, secondary panicle branching, and overall grain yield through improved cytokinin content in the panicle tissue. Under drought conditions, the Osckx2 mutant conserved more water and demonstrated improved water-saving traits. Through reduced transpiration, Osckx2 mutants showed an improved survival response than the wild type to unset dehydration stress. Further, Osckx2 maintained chloroplast and membrane integrity and showed significantly improved photosynthetic function under drought conditions through enhanced antioxidant protection systems. The OsCKX2 function negatively affects panicle grain number and drought tolerance, with no discernible impact in response to salinity. The finding suggests the utility of the beneficial Osckx2 allele in breeding to develop climate-resilient, high-yielding cultivars for future food security.

The effects of monoculture and intercropping on photosynthesis performance correlated with growth of garlic and perennial ryegrass response to different heavy metals.

BACKGROUND: The potential of phytoremediation using garlic monoculture (MC) and intercropping (IC) system with perennial ryegrass to enhance the uptake of cadmium (Cd), chromium (Cr), and lead (Pb) were investigated. RESULTS: Positive correlations were found between MC and IC systems, with varying biomass. Production of perennial ryegrass was affected differently depending on the type of toxic metal present in the soil. Root growth inhibition was more affected than shoot growth inhibition. The total biomass of shoot and root in IC was higher than MC, increasing approximately 3.7 and 2.9 fold compared to MC, attributed to advantages in root IC crop systems. Photosystem II efficiency showed less sensitivity to metal toxicity compared to the control, with a decrease between 10.07-12.03%. Among gas exchange parameters, only Cr significantly affected physiological responses by reducing transpiration by 69.24%, likely due to leaf chlorosis and necrosis. CONCLUSION: This study exhibited the potential of garlic MC and IC with perennial ryegrass in phytoremediation. Although the different metals affect plant growth differently, IC showed advantages over MC in term biomass production.

Transcriptome profiling reveals the impact of various levels of biochar application on the growth of flue-cured tobacco plants.

BACKGROUND: Biochar, a carbon-rich source and natural growth stimulant, is usually produced by the pyrolysis of agricultural biomass. It is widely used to enhance plant growth, enzyme activity, and crop productivity. However, there are no conclusive studies on how different levels of biochar application influence these systems. METHODS AND RESULTS: The present study elucidated the dose-dependent effects of biochar application on the physiological performance, enzyme activity, and dry matter accumulation of tobacco plants via field experiments. In addition, transcriptome analysis was performed on 60-day-old (early growth stage) and 100-day-old (late growth stage) tobacco leaves to determine the changes in transcript levels at the molecular level under various biochar application levels (0, 600, and 1800 kg/ha). The results demonstrated that optimum biochar application enhances plant growth, regulates enzymatic activity, and promotes biomass accumulation in tobacco plants, while higher biochar doses had adverse effects. Furthermore, transcriptome analysis revealed a total of 6561 differentially expressed genes (DEGs) that were up- or down-regulated in the groupwise comparison under different treatments. KEGG pathways analysis demonstrated that carbon fixation in photosynthetic organisms (ko00710), photosynthesis (ko00195), and starch and sucrose metabolism (ko00500) pathways were significantly up-regulated under the optimal biochar dosage (600 kg/ha) and down-regulated under the higher biochar dosage (1800 kg/ha). CONCLUSION: Collectively, these results indicate that biochar application at an optimal rate (600 kg/ha) could positively affect photosynthesis and carbon fixation, which in turn increased the synthesis and accumulation of sucrose and starch, thus promoting the growth and dry matter accumulation of tobacco plants. However, a higher biochar dosage (1800 kg/ha) disturbs the crucial source-sink balance of organic compounds and inhibits the growth of tobacco plants.

Genetic Analysis and Fine Mapping of a New Rice Mutant, Leaf Tip Senescence 2.

Premature leaf senescence significantly reduces rice yields. Despite identifying numerous factors influencing these processes, the intricate genetic regulatory networks governing leaf senescence demand further exploration. We report the characterization of a stably inherited, ethyl methanesulfonate(EMS)-induced rice mutant with wilted leaf tips from seedling till harvesting, designated lts2. This mutant exhibits dwarfism and early senescence at the leaf tips and margins from the seedling stage when compared to the wild type. Furthermore, lts2 displays a substantial decline in both photosynthetic activity and chlorophyll content. Transmission electron microscopy revealed the presence of numerous osmiophilic granules in chloroplast cells near the senescent leaf tips, indicative of advanced cellular senescence. There was also a significant accumulation of H2O2, alongside the up-regulation of senescence-associated genes within the leaf tissues. Genetic mapping situated lts2 between SSR markers Q1 and L12, covering a physical distance of approximately 212 kb in chr.1. No similar genes controlling a premature senescence leaf phenotype have been identified in the region, and subsequent DNA and bulk segregant analysis (BSA) sequencing analyses only identified a single nucleotide substitution (C-T) in the exon of LOC_Os01g35860. These findings position the lts2 mutant as a valuable genetic model for elucidating chlorophyll metabolism and for further functional analysis of the gene in rice.

Optimization of salicylic acid concentrations for increasing antioxidant enzymes and bioactive compounds of Agastache rugosa in a plant factory.

Salicylic acid (SA) plays a crucial role as a hormone in plants and belongs to the group of phenolic compounds. Our objective was to determine the optimal concentration of SA for enhancing the production of bioactive compounds in Agastache rugosa plants while maintaining optimal plant growth. The plants underwent SA soaking treatments at different concentrations (i.e., 0, 100, 200, 400, 800, and 1600 µmol mol-1) for 10 min at 7 days after they were transplanted. We observed that elevated levels of SA at 800 and 1600 µmol mol-1 induced oxidative stress, leading to a significant reduction across many plant growth variables, including leaf length, width, number, area, shoot fresh weight (FW), stem FW and length, and whole plant dry weights (DW) compared with that in the control plants. Additionally, the treatment with 1600 µmol mol-1 SA resulted in the lowest values of flower branch number, FW and DW of flowers, and DW of leaf, stem, and root. Conversely, applying 400 µmol mol-1 SA resulted in the greatest increase of chlorophyll (Chl) a and b, total Chl, total flavonoid, total carotenoid, and SPAD values. The photosynthetic rate and stomatal conductance decreased with increased SA concentrations (i.e., 800 and 1600 µmol mol-1). Furthermore, the higher SA treatments (i.e., 400, 800, and 1600 µmol mol-1) enhanced the phenolic contents, and almost all SA treatments increased the antioxidant capacity. The rosmarinic acid content peaked under 200 µmol mol-1 SA treatment. However, under 400 µmol mol-1 SA, tilianin and acacetin contents reached their highest levels. These findings demonstrate that immersing the roots in 200 and 400 µmol mol-1 SA enhances the production of bioactive compounds in hydroponically cultivated A. rugosa without compromising plant growth. Overall, these findings provide valuable insights into the impact of SA on A. rugosa and its potential implications for medicinal plant cultivation and phytochemical production.

Deciphering desiccation tolerance in wild eggplant species: insights from chlorophyll fluorescence dynamics.

BACKGROUND: Climate change exacerbates abiotic stresses, which are expected to intensify their impact on crop plants. Drought, the most prevalent abiotic stress, significantly affects agricultural production worldwide. Improving eggplant varieties to withstand abiotic stress is vital due to rising drought from climate change. Despite the diversity of wild eggplant species that thrive under harsh conditions, the understanding of their drought tolerance mechanisms remains limited. In the present study, we used chlorophyll fluorescence (ChlaF) imaging, which reveals a plant's photosynthetic health, to investigate desiccation tolerance in eggplant and its wild relatives. Conventional fluorescence measurements lack spatial heterogeneity, whereas ChlaF imaging offers comprehensive insights into plant responses to environmental stresses. Hence, employing noninvasive imaging techniques is essential for understanding this heterogeneity. RESULTS: Desiccation significantly reduced the leaf tissue moisture content (TMC) across species. ChlaF and TMC displayed greater photosystem II (PSII) efficiency after 54 h of desiccation in S. macrocarpum, S. torvum, and S. indicum, with S. macrocarpum demonstrating superior efficiency due to sustained fluorescence. PSII functions declined gradually in S. macrocarpum and S. torvum, unlike those in other species, which exhibited abrupt declines after 54 h of desiccation. However, after 54 h, PSII efficiency remained above 50% of its initial quantum yield in S. macrocarpum at 35% leaf RWC (relative water content), while S. torvum and S. indicum displayed 50% decreases at 31% and 33% RWC, respectively. Conversely, the susceptible species S. gilo and S. sisymbriifolium exhibited a 50% reduction in PSII function at an early stage of 50% RWC, whereas in S. melongena, this reduction occurred at 40% RWC. CONCLUSION: Overall, our study revealed notably greater leaf desiccation tolerance, especially in S. macrocarpum, S. torvum, and S. indicum, attributed to sustained PSII efficiency at low TMC levels, indicating that these species are promising sources of drought tolerance.

Vegetation growth responses to climate change: A cross-scale analysis of biological memory and time lags using tree ring and satellite data.

Vegetation growth is affected by past growth rates and climate variability. However, the impacts of vegetation growth carryover (VGC; biotic) and lagged climatic effects (LCE; abiotic) on tree stem radial growth may be decoupled from photosynthetic capacity, as higher photosynthesis does not always translate into greater growth. To assess the interaction of tree-species level VGC and LCE with ecosystem-scale photosynthetic processes, we utilized tree-ring width (TRW) data for three tree species: Castanopsis eyrei (CE), Castanea henryi (CH, Chinese chinquapin), and Liquidambar formosana (LF, Chinese sweet gum), along with satellite-based data on canopy greenness (EVI, enhanced vegetation index), leaf area index (LAI), and gross primary productivity (GPP). We used vector autoregressive models, impulse response functions, and forecast error variance decomposition to analyze the duration, intensity, and drivers of VGC and of LCE response to precipitation, temperature, and sunshine duration. The results showed that at the tree-species level, VGC in TRW was strongest in the first year, with an average 77% reduction in response intensity by the fourth year. VGC and LCE exhibited species-specific patterns; compared to CE and CH (diffuse-porous species), LF (ring-porous species) exhibited stronger VGC but weaker LCE. For photosynthetic capacity at the ecosystem scale (EVI, LAI, and GPP), VGC and LCE occurred within 96 days. Our study demonstrates that VGC effects play a dominant role in vegetation function and productivity, and that vegetation responses to previous growth states are decoupled from climatic variability. Additionally, we discovered the possibility for tree-ring growth to be decoupled from canopy condition. Investigating VGC and LCE of multiple indicators of vegetation growth at multiple scales has the potential to improve the accuracy of terrestrial global change models.

Mycorrhization enhances plant growth and stabilizes biomass allocation under drought.

Plants and their symbionts, such as arbuscular mycorrhizal (AM) fungi, are increasingly subjected to various environmental stressors due to climate change, including drought. As a response to drought, plants generally allocate more biomass to roots over shoots, thereby facilitating water uptake. However, whether this biomass allocation shift is modulated by AM fungi remains unknown. Based on 5691 paired observations from 154 plant species, we conducted a meta-analysis to evaluate how AM fungi modulate the responses of plant growth and biomass allocation (e.g., root-to-shoot ratio, R/S) to drought. We found that AM fungi attenuate the negative impact of drought on plant growth, including biomass production, photosynthetic performance and resource (e.g. nutrient and water) uptake. Accordingly, drought significantly increased R/S in non-inoculated plants, but not in plants symbiotic with established AM fungal symbioses. These results suggest that AM fungi promote plant growth and stabilize their R/S through facilitating nutrient and water uptake in plants under drought. Our findings highlight the crucial role of AM fungi in enhancing plant resilience to drought by optimizing resource allocation. This knowledge opens avenues for sustainable agricultural practices that leverage symbiotic relationships for climate adaptation.

Phosphate solubilizing Aspergillus Niger PH1 ameliorates growth and alleviates lead stress in maize through improved photosynthetic and antioxidant response.

Among the several threats to humanity by anthropogenic activities, contamination of the environment by heavy metals is of great concern. Upon entry into the food chain, these metals cause serious hazards to plants and other organisms including humans. Use of microbes for bioremediation of the soil and stress mitigation in plants are among the preferred strategies to provide an efficient, cost-effective, eco-friendly solution of the problem. The current investigation is an attempt in this direction where fungal strain PH1 was isolated from the rhizosphere of Parthenium hysterophorus which was identified as Aspergillus niger by sequence homology of the ITS 1 and ITS 4 regions of the rRNA. The strain was tested for its effect on growth and biochemical parameters as reflection of its potential to mitigate Pb stress in Zea mays exposed to 100, 200 and 500 µg of Pb/g of soil. In the initial screening, it was revealed that the strain has the ability to tolerate lead stress, solubilize insoluble phosphate and produce plant growth promoting hormones (IAA and SA) and other metabolites like phenolics, flavonoids, sugar, protein and lipids. Under 500 µg of Pb/g of soil, Z. mays exhibited significant growth retardation with a reduction of 31% in root length, 30.5% in shoot length, 57.5% in fresh weight and 45.2% in dry weight as compared to control plants. Inoculation of A. niger to Pb treated plants not only restored root and shoot length, rather promoted it to a level significantly higher than the control plants. Association of the strain modulated the physio-hormonal attributes of maize plants that resulted in their better growth which indicated a state of low stress. Additionally, the strain boosted the antioxidant defence system of the maize there by causing a significant reduction in the ascorbic acid peroxidase (1.5%), catalase (19%) and 1,1-diphenyl-2 picrylhydrazyl (DPPH) radical scavenging activity (33.3%), indicating a lower stress condition as compared to their non-inoculated stressed plants. Based on current evidence, this strain can potentially be used as a biofertilizer for Pb-contaminated sites where it will improve overall plant health with the hope of achieving better biological and agricultural yields.

Evolution: Spectral speciation.

Speciation is a complex process sparked by multitudes of environmental stressors and culminating in adaptive, and perhaps novel, phenotypic traits. A new study presents evidence supporting spectral niche-partitioning in a cyanobacterial clade specializing in far-red photosynthesis.

Foliar-applied melatonin and titanium nanoparticles modulate cadmium (Cd) toxicity through minimizing Cd accumulation and optimizing physiological and biochemical properties in sage (Salvia officinalis L.).

Notwithstanding the fact that melatonin (MT) and titanium nanoparticles (Ti NPs) alone have been widely used recently to modulate cadmium (Cd) stress in plants, there is a gap in the comparative impacts of these materials on lowering Cd toxicity in sage plants. The objective of this study was to determine how foliar application of MT and Ti NPs affected the growth, Cd accumulation, photosynthesis, water content, lipid peroxidation, and essential oil (EO) quality and quantity of sage plants in Cd-contaminated soils. A factorial experiment was conducted using MT at 100 and 200 µM and Ti NPs at 50 and 100 mg L-1 topically, together with Cd toxicity at 10 and 20 mg Cd kg-1 soil. The results showed that Cd toxicity decreased plant growth and enhanced lipid peroxidation. The Cd stress at 20 mg kg-1 soil resulted in increases in Cd root (693%), Cd shoot (429%), electrolyte leakage (EL, 29%), malondialdehyde (MDA, 72%), shoot weight (31%), root weight (27%), chlorophyll (Chl) a + b (26%), relative water content (RWC, 23%), and EO yield (30%). The application of MT and Ti NPs controlled drought stress by reducing MDA and EL, enhancing plant weight, Chl, RWC, and EO production, and minimizing Cd accumulation in plant tissues. The predominant compounds in the EO were α-thujone, 1,8-cineole, ß-thujone, camphor, and α-humulene. MT and Ti NPs caused α-thujone to rise, whereas Cd stress caused it to fall. Based on heat map analysis, MDA was the trait that was most sensitive to treatments. In summary, the research emphasizes the possibility of MT and Ti NPs, particularly MT at 200 µM, to mitigate Cd toxicity in sage plants and enhance their biochemical reactions.

Physiological, transcriptomic and metabolomic insights of three extremophyte woody species living in the multi-stress environment of the Atacama Desert.

MAIN CONCLUSIONS: In contrast to Neltuma species, S. tamarugo exhibited higher stress tolerance, maintaining photosynthetic performance through enhanced gene expression and metabolites. Differentially accumulated metabolites include chlorophyll and carotenoids and accumulation of non-nitrogen osmoprotectants. Plant species have developed different adaptive strategies to live under extreme environmental conditions. Hypothetically, extremophyte species present a unique configuration of physiological functions that prioritize stress-tolerance mechanisms while carefully managing resource allocation for photosynthesis. This could be particularly challenging under a multi-stress environment, where the synthesis of multiple and sequential molecular mechanisms is induced. We explored this hypothesis in three phylogenetically related woody species co-occurring in the Atacama Desert, Strombocarpa tamarugo, Neltuma alba, and Neltuma chilensis, by analyzing their leaf dehydration and freezing tolerance and by characterizing their photosynthetic performance under natural growth conditions. Besides, the transcriptomic profiling, biochemical analyses of leaf pigments, and metabolite analysis by untargeted metabolomics were conducted to study gene expression and metabolomic landscape within this challenging multi-stress environment. S. tamarugo showed a higher photosynthetic capacity and leaf stress tolerance than the other species. In this species, a multifactorial response was observed, which involves high photochemical activity associated with a higher content of chlorophylls and ß-carotene. The oxidative damage of the photosynthetic apparatus is probably attenuated by the synthesis of complex antioxidant molecules in the three species, but S. tamarugo showed the highest antioxidant capacity. Comparative transcriptomic and metabolomic analyses among the species showed the differential expression of genes involved in the biosynthetic pathways of key stress-related metabolites. Moreover, the synthesis of non-nitrogen osmoprotectant molecules, such as ciceritol and mannitol in S. tamarugo, would allow the nitrogen allocation to support its high photosynthetic capacity without compromising leaf dehydration tolerance and freezing stress avoidance.

Nitrogen deposition differentially regulates the sensitivity of gross primary productivity to extreme drought versus wetness.

Global hydroclimatic variability is increasing with more frequent extreme dry and wet years, severely destabilizing terrestrial ecosystem productivity. However, what regulates the consequence of precipitation extremes on productivity remains unclear. Based on a 9-year field manipulation experiment on the Qinghai-Tibetan Plateau, we found that the responses of gross primary productivity (GPP) to extreme drought and wetness were differentially regulated by nitrogen (N) deposition. Over increasing N deposition, extreme dry events reduced GPP more. Among the 12 biotic and abiotic factors examined, this was mostly explained by the increased plant canopy height and proportion of drought-sensitive species under N deposition, making photosynthesis more sensitive to hydraulic stress. While extreme wet events increased GPP, their effect did not shift over N deposition. These site observations were complemented by a global synthesis derived from the GOSIF GPP dataset, which showed that GPP sensitivity to extreme drought was larger in ecosystems with higher N deposition, but GPP sensitivity to extreme wetness did not change with N deposition. Our findings indicate that intensified hydroclimatic variability would lead to a greater loss of land carbon sinks in the context of increasing N deposition, due to that GPP losses during extreme dry years are more pronounced, yet without a synchronous increase in GPP gains during extreme wet years. The study implies that the conservation and management against climate extremes merit particular attention in ecosystems subject to N deposition.

Disrupted H2 synthesis combined with methyl viologen treatment inhibits photosynthetic electron flow to synergistically enhance glycogen accumulation in the cyanobacterium Synechocystis sp. PCC 6803.

Under nitrogen deprivation (-N), cyanobacterium Synechocystis sp. PCC 6803 exhibits growth arrest, reduced protein content, and remarkably increased glycogen accumulation. However, producing glycogen under this condition requires a two-step process with cell transfer from normal to -N medium. Metabolic engineering and chemical treatment for rapid glycogen accumulation can bypass the need for two-step cultivation. For example, recent studies indicate that individually disrupting hydrogen (H2) or poly(3-hydroxybutyrate) (PHB) synthesis, or treatment with methyl viologen (MV), effectively increases glycogen accumulation in Synechocystis. Here we explore the effects of disrupted H2 or poly(3-hydroxybutyrate) synthesis, together with MV treatment to on enhanced glycogen accumulation in Synechocystis grown in normal medium. Wild-type cells without MV treatment exhibited low glycogen content of less than 6% w/w dry weight (DW). Compared with wild type, disrupting PHB synthesis combined with MV treatment did not increase glycogen content. Disrupted H2 production without MV treatment yielded up to 11% w/w DW glycogen content. Interestingly, when combined, disrupted H2 production with MV treatment synergistically enhanced glycogen accumulation to 51% and 59% w/w DW within 3 and 7 days, respectively. Metabolomic analysis suggests that MV treatment mediated the conversion of proteins into glycogen. Metabolomic and transcriptional-expression analysis suggests that disrupted H2 synthesis under MV treatment positively influenced glycogen synthesis. Disrupted H2 synthesis under MV treatment significantly increased NADPH levels. This increased NADPH content potentially contributed to the observed enhancements in antioxidant activity against MV-induced oxidants, O2 evolution, and metabolite substrates levels for glycogen synthesis in normal medium, ultimately leading to enhanced glycogen accumulation in Synechocystis. KEY MESSAGE: Combining disrupted hydrogen-gas synthesis and the treatment by photosynthesis electron-transport inhibitor significantly enhance glycogen production in cyanobacteria.

The Effecting Mechanisms of 100 nm Sized Polystyrene Nanoplastics on the Typical Coastal Alexandrium tamarense.

Due to the increase in nanoplastics (NPs) abundance in aquatic environments, their effects on phytoplankton have aroused large research attention. In this study, 100 nm sized polystyrene NPs were chosen to investigate their effecting performance and mechanisms on a typical dinoflagellates Alexandrium tamarense. The results indicated the population growth and photosynthetic efficiencies of A. tamarense were significantly inhibited by NPs exposure, as well as the increase in cellular total carotenoids and paralytic shellfish toxins (PSTs). Meanwhile, the cellar ROS levels increased, corresponding to the increased activities or contents of multiple antioxidant components, including SOD, CAT, GPX, GR, GSH and GSSG. The transcriptional results support the physiological-biochemical results and further revealed the down-regulation of genes encoding the light reaction centers (PSI and PSII) and up-regulation of genes encoding the antioxidant components. Up-regulation of genes encoding key enzymes of the Calvin cycle and glycolytic pathway together with the TCA cycle could accelerate organic carbon and ATP production for A. tamarense cells resistant to NPs stress. Finally, more Glu and acetyl-CoA produced by the enhanced GSH cycle and the glycolytic pathway, respectively, accompanied by the up-regulation of Glu and Arg biosynthesis genes supported the increase in the PST contents under NPs exposure. This study established a data set involving physiological-biochemical changes and gene information about marine dinoflagellates responding to NPs, providing a data basis for further evaluating the ecological risk of NPs in marine environments.