Photochemical Efficiency Research Articles

Transcriptomic profiling reveals the contribution of Nitric Oxide to maintaining photosynthesis and antioxidant ability in Hylotelephium erythrostictum leaves under salt stress

Hylotelephium erythrostictum is a plant species with high garden value and notable salt tolerance, yet the salt tolerance mechanism is poorly understood. In this study, we treated the plants under salt stress with exogenous nitric oxide (NO) and discovered that the content of malondialdehyde (MDA) decreased, while soluble sugar increased. The chlorophyll fluorescence parameters, such as the maximum photochemical efficiency of PS II (Fv/Fm), actual quantum yield Y(II), and the photochemical quenching coefficient (qP) increased, whereas the non-photochemical quenching coefficient (NPQ) decreased. Afterthat, we performed transcriptome sequencing on leaves treated with 200 mM NaCl after 0, 5, and 10 d. A total of 124,008 unigenes were identified and functionally annotated. Transcripts related to NO synthase exhibited increased expression levels, and transcripts related to superoxide dismutase (SOD) and catalase (CAT) were also significantly upregulated. In contrast, the majority of the differently expressed genes (DEGs) associated with photosynthesis and photosynthesis-antenna protein metabolic pathways were downregulated. Furthermore, the expression levels of HeSOD2, HeCAT2, HeCab1, and HepsaA were significantly upregulated. These results suggest that NO enhances the photosynthetic and antioxidant capacity of H. erythrostictum and improves salt tolerance. Our study will lead to a better understanding of how this plant responds to stressful conditions and potentially develop ways to enhance its salt tolerance by identifying salt-tolerance genes.

Application of prohexadione-calcium priming affects Brassica napus L. seedlings by regulating morph-physiological characteristics under salt stress.

Salinity stress imposes severe constraints on plant growth and development. Here, we explored the impacts of prohexadione-calcium (Pro-Ca) on rapeseed growth under salt stress. We designed a randomized block design pot experiment using two rapeseed varieties, 'Huayouza 158R' and 'Huayouza 62'. We conducted six treatments, S0: non-primed + 0 mM NaCl, Pro-Ca+S0: Pro-Ca primed + 0 mM NaCl, S100: non-primed + 100 mM NaCl, Pro-Ca+S100: Pro-Ca primed + 100 mM NaCl, S150: non-primed + 150 mM NaCl, Pro-Ca+S150: Pro-Ca primed + 150 mM NaCl. The morphophysiological characteristics, and osmoregulatory and antioxidant activities were compared for primed and non-primed varieties. Our data analysis showed that salt stress induced morph-physiological traits and significantly reduced the antioxidant enzyme activities in both rapeseed varieties. The Pro-Ca primed treatment significantly improved seedlings, root, and shoot morphological traits and accumulated more dry matter biomass under salt stress. Compared to Huayouza 158R, Huayouza 62 performed better with the Pro-Ca primed treatment. The Pro-Ca primed treatment significantly enhanced chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and actual photochemical quantum efficiency (ФPSII). Furthermore, the Pro-Ca primed treatment also improved ascorbic acid (ASA) content, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) activity, and stimulated the accumulation of soluble proteins. These findings strongly suggested that the Pro-Ca primed treatment may effectively counteract the negative impacts of salinity stress by regulating the morph-physiological and antioxidant traits.

Rootstock influences on growth and bearing precocity in juvenile cocoa

Within the cocoa germplasm used for variety development in West Africa, knowledge of varieties that are suitable as rootstocks to promote growth and precocity of clones is lacking. Six cocoa varieties were used to generate 36 clones for evaluation. For each of the six scions selected as ortets from previous progeny trials, the corresponding seed-derived family was regenerated through manual pollinations. The scions were grafted in a full diallel fashion on each of the six seed-derived family, and field evaluated in four replications following a randomized complete block design. Also, seed-derived varieties were evaluated in the nursery for vigour characteristics, and under similar conditions as the 36 clones in the field. Genotype heterozygosity at 72 SNP loci was significantly correlated with vigour characteristics of the six varieties. Seed-derived varieties of high vigour benefited clone performance for vigour, and dry bean yield when used as rootstocks but not as scion. The maximum photochemical efficiency of photosystem II (Fv/Fm) was different among seed-derived varieties and clones in the dry season but not the rainy season. Among clones, higher Fv/Fm values were associated with higher-vigour rootstock varieties. Diallel grafting model enabled partitioning of total variance into several sub-components. The variance due to specific compatibility ability was not significant for any of the measured traits. Decomposition of the reciprocal variance revealed that significant reciprocal effects were mainly due to significant maternal (rootstock) effects. The key finding is that, for any scion, the most precocious clone is obtained by grafting on high vigour rootstock varieties.

High-nitrogen fertilizer alleviated adverse effects of drought stress on the growth and photosynthetic characteristics of Hosta ‘Guacamole’

BackgroundSeveral plants are facing drought stress due to climate change in recent years. In this study, we aimed to explore the effect of varying watering frequency on the growth and photosynthetic characteristics of Hosta ‘Guacamole’. Moreover, we investigated the effect of high-nitrogen and -potassium fertilizers on alleviating the impacts of drought stress on the morphology, photosynthetic characteristics, chlorophyll fluorescence, fast chlorophyll a fluorescence transient, JIP-test parameters, and enzymatic and non-enzymatic scavenging system for reactive oxygen species (ROS) in this species.ResultsLeaf senescence, decreased chlorophyll contents, limited leaf area, and reduced photosynthetic characteristics and oxygen-evolving complex (OEC) activity were observed in Hosta ‘Guacamole’ under drought stress. However, high-nitrogen fertilizer (30-10-10) could efficiently alleviate and prevent the adverse effects of drought stress. High-nitrogen fertilizer significantly increased chlorophyll contents, which was higher by 106% than drought stress. Additionally, high-nitrogen fertilizer significantly improved net photosynthetic rate and water use efficiency, which were higher by 467% and 2900% than those under drought stress. It attributes that high-nitrogen fertilizer could reduce transpiration rate of leaf cells and stomatal opening size in drought stress. On the other hand, high-nitrogen fertilizer enhanced actual photochemical efficiency of PS II and photochemical quenching coefficient, and actual photochemical efficiency of PS II significantly higher by 177% than that under drought stress. Furthermore, high-nitrogen fertilizer significantly activated OEC and ascorbate peroxidase activities, and enhanced the performance of photosystem II and photosynthetic capacity compared with high-potassium fertilizers (15-10-30).ConclusionsHigh-nitrogen fertilizer (30-10-10) could efficiently alleviate the adverse effects of drought stress in Hosta ‘Guacamole’ via enhancing OEC activity and photosynthetic performance and stimulating enzymatic ROS scavenging system.

Growth and metabolic differences in the potential of phytoremediation between two hybrid bermudagrasses in roots, stems, and leaves under cadmium stress

Bermudagrass (Cynodon) species has been identified as a dominant plant species in cadmium (Cd)-contaminated soils. Objectives of current study were to evaluate Cd tolerance of two hybrid bermudagrass (Cynodon transvaalensis × Cynodon dactylon) cultivars Tifdwarf and Chuannong-3 for urban greening and slope ecological restoration and further to explore the difference in Cd tolerance associated with changes in ion absorption and distribution, antioxidant metabolism, and accumulations of phytochelatins (PCs) and metallothioneins (MTs) in roots, stems, and leaves. After exposure to equal concentration and duration of Cd stress, growth, chlorophyll content, and photochemical efficiency of both cultivars reduced significantly, but Cd-induced these inhibitory effects were more pronounced in Chuannong-3. As compared to Chuannong-3, Tifdwarf maintained significantly higher Cd concentration in roots and lower Cd concentration, bioconcentration factor, and translocation factor in aboveground parts in response to Cd stress. Each plant of Tifdwarf also accumulated more Cd in leaves, stems, and roots than each plant of Chuannong-3 due to larger biomass under Cd stress. Cd stress also significantly inhibited uptake and partitioning of iron, sodium, and potassium in two cultivars. In addition, Tifdwarf exhibited better antioxidant defense for reactive oxygen species (ROS) scavenging than Chuannong-3 under Cd stress, as reflected by higher antioxidant enzyme activities and antioxidant metabolites involved in ascorbic acid (ASA)-glutathione (GSH) cycle. Tifdwarf also accumulated more PCs in leaves, stems, and roots and more MTs in leaves and stems than Chuannong-3, which could help to chelate Cd to reduce cytotoxicity of Cd. Moreover, strong antioxidant property of MTs was beneficial for maintaining ROS homeostasis in plants. Therefore, better Cd tolerance of Tifdwarf could be mainly due to the inhibition of Cd uptake and partitioning, enhanced ASA-GSH cycle, and more accumulations of PCs and MTs. Tifdwarf showed better potential for Cd remediation or urban greening in Cd-polluted soils.

Effect of growth promotors on morphogenesis, photosynthetic apparatus, productivity and residual substances content in sweet pepper (Capsicum annuum) fruits

The use of plant growth promoting substances in order to optimize crop performance is one of the leading tasks of modern plant physiology. The effect of 0.005% 1-naphthaleneacetic acid (1-NAA), 0.005% gibberellic acid (GA3), 0.005% 6-benzylaminopurine (6-BAP) foliar treatment on morphogenesis, leaf parameters, photosynthetic pigments content, photosynthetic apparatus activity indices, and residual amounts of the used substances in the sweet pepper Capsicum annuum L. variety Antey fruits was investigated. The field experiment was laid on plots of 32 m2. The treatment of plants was carried out at the budding stage. Morphometric indices were determined at the flowering and fruit formation stages. The mesostructure of the middle tier leaves was studied at the fruit formation stage. The content of the chlorophylls was determined in the fresh leaf tissue by the spectrophotometric method. Indices of photosystem II (PSII) activity were determined by registration of chlorophyll fluorescence induction, using a portable single-beam fluorimeter. The assay of the residual content growth of promotors in the fruits was carried out on a Shimadzu GC gas chromatograph with a mass spectrometric detector – GCMS-QP2020 EI. It was revealed that treatment with GA3 increased plant height. All substances increased the number of leaves on the plant, their fresh and dry weight, the leaf area, and the canopy leaf area index. All growth promoting substances thickened leaf laminas due to the growth of chlorenchyma. GA3 and 6-BAP increased the volume of columnar parenchyma cells, and 1-NAA and GA3 increased the size of leaf spongy parenchyma cells. 6-BAP increased the total chlorophyll (a + b) content in the leaves, and under the GA3 treatment this index tended to decrease. 6-BAP increased the chlorophyll index of plants at the fruit formation stage, and GA3 decreased it at the flowering stage. The net photosynthetic rate increased under the influence of 1-NAA and 6-BAP, and decreased under GA3 treatment. GA3 reduced photorespiration and transpiration in leaves, 6-BAP increased transpiration, and 1-NAA decreased it. All substances increased dark respiration. Treatment with GA3 and 6-BAP reliably increased the maximum quantum efficiency of PSII photochemical reactions. 1-NAA and 6-BAP increased the actual quantum efficiency of PSII photochemistry. The coefficient of chlorophyll fluorescence photochemical quenching significantly increased at flowering under the application of 1-NAA, and tended to increase at the stage of fruit formation under the treatment of 1-NAA and 6-BAP. When GA3 was applied, the rate of chlorophyll fluorescence photochemical quenching was significantly reduced. The index of PSII reaction centers fraction that do not reduce the QB acceptor did not change with the use of 1-NAA and GA3 and tended to decrease after the use of 6-BAP. All growth promotors increased the whole plant dry weight. They reduced the net photosynthetic efficiency at the flowering stage, and at the stage of fruit formation it significantly increased under the treatment with 6-BAP. The 6-BAP caused the redistribution of plastic substances into the fruits due to the decrease in the dry weight of vegetative organs. Treatment with 1-NAA increased the proportion of root dry weight. 1-NAA, GA3 and 6-BAP increased the yield of fruits from one plant by 17%, 22% and 20% respectively due to the increase in the number of fruits per plant. The residual amounts of 1-NAA and 6-BAP in ripe sweet pepper fruits did not exceed the maximum permissible sanitary standards.

Ácido salicílico reduz os efeitos prejudiciais do estresse salino em Tropaeolum majus

ABSTRACT Salt stress hampers the growth and physiology of nasturtium (Tropaeolum majus), due to biochemical, physiological, and anatomical disruptions. The application of salicylic acid stands as an alternative to alleviate the detrimental effects of salt stress, but studies on nasturtium are scarce. Thus, the aim of present study was to assess the effects of foliar application of salicylic acid on nasturtium cultivated under salt stress. The experiment followed a completely randomized design in a 3 x 3 factorial scheme, with 0 (no stress), 50 (moderate salt stress), and 100 (severe salt stress) mM of NaCl, and application of 0, 0.5, and 1 mM of salicylic acid, each with six replications. Growth (plant height, stem diameter, and number of leaves), gas exchange (stomatal conductance, photosynthesis, transpiration, internal CO2 concentration, intrinsic water use efficiency, instantaneous water use efficiency, and intrinsic carboxylation efficiency), as well as chlorophyll indices and chlorophyll a fluorescence were evaluated. Salt stress affected the variables analyzed in this study. The application of salicylic acid had a positive effect on mitigating the effects of severe salt stress, resulting in a significant increase in the number of leaves. The most effective dose was 1 mM, also leading to notable improvements in water use efficiency and photochemical efficiency. However, other combinations of salinity and salicylic acid reduced growth and gas exchange in nasturtium plants.

Plant growth-promoting rhizobacteria Pseudomonas aeruginosa HG28-5 improves salt tolerance by regulating Na+/K+ homeostasis and ABA signaling pathway in tomato

Salinity stress badly restricts the growth, yield and quality of vegetable crops. Plant growth-promoting rhizobacteria (PGPR) is a friendly and effective mean to enhance plant growth and salt tolerance. However, information on the regulatory mechanism of PGPR on vegetable crops in response to salt stress is still incomplete. Here, we screened a novel salt-tolerant PGPR strain Pseudomonas aeruginosa HG28–5 by evaluating the tomatoes growth performance, chlorophyll fluorescence index, and relative electrolyte leakage (REL) under normal and salinity conditions. Results showed that HG28–5 colonization improved seedling growth parameters by increasing the plant height (23.7%), stem diameter (14.6%), fresh and dry weight in the shoot (60.3%, 91.1%) and root (70.1%, 92.5%), compared to salt-stressed plants without colonization. Likewise, HG28–5 increased levels of maximum photochemical efficiency of PSII (Fv/Fm) (99.3%), the antioxidant enzyme activities as superoxide dismutase (SOD, 85.5%), peroxidase (POD, 35.2%), catalase (CAT, 20.6%), and reduced the REL (48.2%), MDA content (41.3%) and ROS accumulation in leaves of WT tomatoes under salt stress in comparison with the plants treated with NaCl alone. Importantly, Na+ content of HG28–5 colonized salt-stressed WT plants were decreased by15.5% in the leaves and 26.6% in the roots in the corresponding non-colonized salt-stressed plants, which may be attributed to the higher K+ concentration and SOS1, SOS2, HKT1;2, NHX1 transcript levels in leaves of colonized plants under saline condition. Interestingly, increased abscisic acid (ABA) content and upregulation of ABA pathway genes (ABA synthesis-related genes NCED1, NCED2, NCED4, NECD6 and signal genes ABF4, ABI5, and AREB) were observed in HG28–5 inoculated salt-stressed WT plants. ABA-deficient mutant (not) with NCED1 deficiency abolishes the effect of HG28–5 on alleviating salt stress in tomato, as exhibited by the substantial rise of REL and ROS accumulation and sharp drop of Fv/Fm in the leaves of not mutant plants. Notably, HG28–5 colonization enhances tomatoes fruit yield by 54.9% and 52.4% under normal and saline water irrigation, respectively. Overall, our study shows that HG28–5 colonization can significantly enhance salt tolerance and improved fruit yield by a variety of plant protection mechanism, including reducing oxidative stress, regulating plant growth, Na+/K+ homeostasis and ABA signaling pathways in tomato. The findings not only deepen our understanding of PGPR regulation plant growth and salt tolerance but also allow us to apply HG28–5 as a microbial fertilizer for agricultural production in high-salinity areas.

Effects of Penoxsulam on Photosynthetic Characteristics and Safety Evaluation of Foxtail Millet

Foxtail millet planting has a long history and profound role in agricultural civilization. However, weeds have become one of the obstacles restricting the development of the foxtail millet industry. Penoxsulam, as an early post-emergence herbicide for controlling gramineous weeds in paddy fields, is effective for some broadleaf weeds. In this study, six different doses (CK, 0.5X, 1X, 2X, 3X, 4X) of penoxsulam were sprayed at the 3–5 leaf stage of the conventional variety Jingu 21 to study its effect on the growth and development of foxtail millet, in order to screen out the appropriate spraying concentration. The main results are as follows: Within 15 days after spraying penoxsulam, the plant height and leaf area of foxtail millet decreased with the increase in spraying dose, and gradually recovered 15–25 days after spraying, but there were still significant differences compared with CK. The photosynthetic pigment content, net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), the maximum photochemical efficiency (Fv/Fm), photosynthetic system II actual photochemical efficiency (Y(II)), and photochemical quenching coefficient (qP) of foxtail millet decreased with an increase in the penoxsulam spraying dose, while the intercellular CO2 concentration (Ci) and non-photochemical quenching coefficient (NPQ) showed an upward trend. There was almost no significant difference in each index between the spraying dose of 0.5X and 1X and CK, but the photosynthesis of foxtail millet leaves was still significantly inhibited under a spraying dose of 3X and 4X. Penoxsulam had certain growth-inhibiting effects on Echinochloa crus-galli (L.) Beauv. (E. crus-galli), Digitaria sanguinalis (L.) Scop. (D. sanguinalis), Chenopodium album L. (C. album), and Amaranthus retroflexus L. (A. retroflexus) which increased as the spraying dosage increased. Our study found that spraying dose groups of 0.5X and 1X penoxsulam were safe for foxtail millet growth and could be used to control gramineous weeds in fields. Other spraying doses are not recommended in the field due to their serious phytotoxicity to foxtail millet, which provides a new measure for weed control in foxtail millet fields.

Drought priming-induced stress memory improves subsequent drought or heat tolerance via activation of γ-aminobutyric acid-regulated pathways in creeping bentgrass.

Recurrent drought can induce stress memory in plants to induce tolerance to subsequent stress, such as high temperature or drought. Drought priming (DP) is an effective approach to improve tolerance to various stresses; however, the potential mechanism of DP-induced stress memory has not been fully resoved. We examined DP-regulated subsequent drought tolerance or thermotolerance associated with changes in physiological responses, GABA and NO metabolism, heat shock factor(HSF) and dehydrin (DHN) pathways in perennial creeping bentgrass. Plants can recover after two cycle of DP, and DP-treated plants had significantly higher tolerance to subsequent drought or heat stress, with higher leaf RWC, Chl content, photochemical efficiency, and cell membrane stability. DP significantly alleviated oxidative damage through enhancing total antioxidant capacity in response to subsequent drought or heat stress. Endogenous GABA was significantly increased by DP through activating glutamic acid decarboxylase activity and inhibiting GABA transaminase activity. DP also enhanced accumulation of NO, depending on NOS activity, under subsequent drought or heat stress. Transcript levels of multiple transcription factors, heat shock proteins, and DHNs in the HSF and DHN pathways were up-regulated by DP under drought or heat stress, but there were differences between DP-regulated heat tolerance and drought tolerance in these pathways. The findings indicate that under recurrent moderate drought, DP improves subsequent tolerance to drought or heat stress in relation to GABA-regulated pathways, providing new insight into understanding of the role of stress memory in plant adaptation to complex environmental stresses.

Physiological and transcriptomic analysis of tomato in response to sub-optimal temperature stress

ABSTRACT Tomato (Solanum lycopersicum L.) is one of the most important economic crops in China. However, its quality and yield are susceptible to the adverse effects of low temperatures. In our study, two tomato cultivars, showing different tolerance to low temperatures, namely the cold-sensitive tomato cultivar (S708) and cold-tolerant tomato cultivar (T722), were grown at optimal (25/18°C) and sub-optimal (15/10°C) temperature conditions for 5 days. Our study aimed to explore the effect of sub-optimal temperature on fresh weight, chlorophyll content and chlorophyll fluorescence, soluble sugars and proline content of two tomato cultivars. Moreover, we employed RNA-Seq to analyze the transcriptomic response of tomato roots to sub-optimal temperature. The results revealed that S708 showed a more significant reduction in fresh weight, chlorophyll content, photochemical efficiency of PSII (YII), maximum quantum yield of PSII (Fv/Fm), photochemical quenching (qP) and electron transport rate (ETR) compared to T722 under the sub-optimal temperature condition. Notably, T722 maintained higher level of soluble sugars and proline in comparison to S708 uner sub-optimal temperature. RNA-seq data showed that up-regulated DEGs in both tomato cultivars were involved in “plant-pathogen interaction”, “MAPK signaling pathway”, “plant hormone signal transduction”, and “phosphatidylinositol signaling system”. Furthermore, “Amino sugar and nucleotide sugar metabolism” pathway was enriched only in T722. Moreover, under sub-optimal temperature, transcription factor genes and osmoregulation genes showed varying degrees of response in both tomato cultivars. Conclusion: In summary, our results offer detailed insights into the response characteristics of tomato to sub-optimal temperature, providing valuable references for the practical management of tomato crops under sub-optimal temperature condition.

Effect of light stress on maximum photochemical efficiency of photosystem II and chloroplast structure in cryptogams Cladonia mitis and Pleurozium schreberi

Lichens and bryophytes are cosmopolitan organisms found in diverse environments with varying sunlight availability. However, excessive light can be a stress factor for both lichens and bryophytes, as it can damage their photosynthetic apparatus, particularly the chlorophyll a and b pigments located in the chloroplasts. The measurement of photosynthetic activity and the use of fluorescence microscopy allows the assessment of the influence of light as a stress factor on the preservation state of the thallus. The main goal of our research was to determine the changes that occur in the photosynthetic activity and structure of chloroplasts of selected species lichen Cladonia mitis (Sandst.) and moss Pleurozium schreberi (Willd. Ex Brid.) under the influence of different light intensity in laboratory conditions: FL - 100% light, RL - 30% maximum light, and NL - natural sunlight. The results of the two-factor analysis of variance (ANOVA) tests showed a variation in the activities of the selected species over time depending on the amount of light energy supplied. It was also demonstrated that soaking lichens increased their photosynthetic activity, whereas in bryophytes, it had the opposite effect, decreasing it. The microscopic results showed that Cladonia mitis showed the lowest level of chloroplast fluorescence in the strongest and reduced light, which coincides with its low level of photosynthetic activity. The mosses exhibited strong fluorescence activity of the chloroplasts, suggesting its significantly higher resistance to light radiation.

Comparative effectiveness of carbon nanoparticles and biochar in alleviating copper stress in corn (Zea mays L.)

The application of carbon nanoparticles (CNPs) and biochar in agriculture for improving plant health and soil quality and alleviating metal stress offers alternative approaches to meet the ever-increasing demand for food. However, poor understanding of their roles in improving crop production under Cu stress represents a significant obstacle to their wide application in agriculture. To clarify how CNPs and biochar affect corn (Zea mays L.) seed germination, seedling growth, plant health, and nutrient uptake under different Cu stress levels, soil-less Petri-dish and greenhouse soil-based bioassays were conducted. The results revealed that CNPs and biochar stimulated corn seed germination and seedling growth. Besides, they were effective in immobilizing Cu2+ sorption in sandy soil and alleviating Cu stress for plant growth, as shown by the increased plant height and dry biomass. The plant nutrient uptake efficiency (NUE) was significantly increased by CNPs, with a maximum increase of 63.1% for N and 63.3% for K at the highest Cu2+ stress level (400 mg Cu2+ L−1). In contrast, non-significant effects on NUE were observed with biochar treatments regardless of Cu stress levels. Interestingly, CNPs significantly increased plant uptake of Cu in the Petri dish test, while biochar inhibited plant uptake of Cu under both experimental conditions. Principle component analysis (PCA) and Pearson correlation analysis indicated that CNPs mitigated Cu stress mainly by elevating antioxidant enzyme activities, enhancing plant photochemical efficiency, and increasing plant uptake of N and K, while biochar was more likely to reduce bioavailability and uptake of Cu in the plant. These findings have great implications for the application of CNPs and biochar as plant growth stimulators and de-toxicity agents in agriculture.

Effects of Warming and Elevated CO2 on Stomatal Conductance and Chlorophyll Fluorescence of C3 and C4 Coastal Wetland Species

Coastal wetland communities provide valuable ecosystem services such as erosion prevention, soil accretion, and essential habitat for coastal wildlife, but are some of the most vulnerable to the threats of climate change. This work investigates the combined effects of two climate stressors, elevated temperature (ambient, + 1.7 °C, + 3.4 °C, and 5.1 °C) and elevated CO2 (eCO2), on leaf physiological traits of dominant salt marsh plant species. The research took place at the Salt Marsh Accretion Response to Temperature eXperiment (SMARTX) at the Smithsonian Environmental Research Center, which includes two plant communities: a C3 sedge community and a C4 grass community. Here we present data collected over five years on rates of stomatal conductance (gs), quantum efficiency of PSII photochemistry (Fv/Fm), and rates of electron transport (ETRmax). We found that both warming and eCO2 caused declines in all traits, but the warming effects were greater for the C3 sedge. This species showed a strong negative stomatal response to warming in 2017 and 2018 (28% and 17% reduction, respectively in + 5.1 °C). However, in later years the negative response to warming was dampened to < 7%, indicating that S. americanus was able to partially acclimate to the warming over time. In 2022, we found that sedges growing in the combined + 5.1 °C eCO2 plots exhibited more significant declines in gs, Fv/Fm, and ETRmax than in either treatment individually. These results are important for predicting future trends in growth of wetland species, which serve as a large carbon sink that may help mitigate the effects of climate change.

Warming affects leaf light use efficiency and functional traits in alpine plants: evidence from a 4-year in-situ field experiment.

Light use efficiency (LUE) is a crucial determinant of plant productivity, while leaf functional traits directly affect ecosystem functions. However, it remains unclear how climate warming affects LUE and leaf functional traits of dominant species in alpine meadows. We conducted a 4-year in-situ field warming experiment to investigate the eco-physiological characteristics for a dominant species (Elymus nutans) and a common species (Potentilla anserina) on the Tibetan Plateau. The leaf traits, photosynthesis and fluorescence characteristics were measured, along with the soil physical-chemical properties associated with the two species. Experimental warming increased the leaf LUE, maximum photochemical efficiency, non-photochemical quenching, relative water content and specific leaf area for both species. However, there was a decrease in leaf and soil element content. Different species exhibit varying adaptability to warming. Increasing temperature significantly increased the photosynthetic rate, stomatal conductance, transpiration rate, total water content, and specific leaf volume of E. nutans; however, all these traits exhibited an opposite trend in P. anserina. Warming has a direct negative impact on leaf LUE and an indirectly enhances LUE through its effects on leaf traits. The impact of warming on plant photosynthetic capacity is primarily mediated by soil nutrients and leaf traits. These results indicate that the two different species employ distinct adaptive strategies in response to climate change, which are related to their species-specific variations. Such changes can confer an adaptive advantage for plant to cope with environmental change and potentially lead to alterations to ecosystem structure and functioning.

Physiological and Biochemical Responses of Melilotus albus to Saline and Alkaline Stresses

Sweet clover (Melilotus albus) is a high-quality leguminous forage grass with salinity tolerance, drought tolerance, and cold hardiness. We selected four varieties of sweet clover with different sensitivities (061898, 061930, No. 55 white flower, and Ningxia white flower) and analyzed the effects of different concentrations of three sodium salts (Na2CO3, NaHCO3, and NaCl) on their physiology and biochemistry responses. Growth and development indexes (such as germination rate, root length, shoot length), chlorophyll content, osmotic regulators (proline, soluble sugar), malondialdehyde (MDA), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were determined under saline–alkali stress. Seed germination and seedling growth of all four clover species were significantly inhibited under saline–alkali stress. During germination, seed germination rate, root length, and shoot length decreased with increasing saline and alkaline concentration. Under saline–alkali stress, chlorophyll content tended to increase and then decrease, cell damage and death increased, and malondialdehyde, soluble sugar, and proline content tended to increase and then decrease. Moreover, the activities of SOD, POD, and CAT all increased and then decreased. Under Na2CO3 stress, the decrease in chlorophyll content of the resistant variety 061898 was less than in the sensitive Ningxia white flower variety. As the concentrations of Na2CO3, NaHCO3, and NaCl increased, the maximum photochemical efficiency of PSII was significantly affected. The resistant 061898 is capable of maintaining higher photosynthetic efficiency. Furthermore, under treatments with the three kinds of saline–alkali solutions, cell damage and death for Ningxia white flower were greater than in 061898. For 061898, the increases in soluble sugar and proline content were greater and the increase in malondialdehyde content was less, while the antioxidant enzyme activities were higher than those in Ningxia white flower. All four sweet clover varieties had higher stress resistance with neutral than with alkaline salts. When stressed by medium to high saline–alkali concentrations, sweet clover seedlings had increased osmotic substance content, enhanced antioxidant enzyme activity, and regulated physiological metabolism. Additionally, sweet clovers regulated the expression of WRKY33, GH3, CYCD3, OXI1, MKK2, MYC2, JAZ, COI1, PYL, PP2C, TGA, and MPK3 to adapt to the saline–alkali environment and improve saline–alkali tolerance. Our analysis of the sweet clover salinity tolerance mechanism contributes to its further use and is of significant importance for addressing land salinization and promoting sustainable agricultural and pastoral practices in China.

Differential drought tolerance among dichondra (Dichondra repens) genotypes in relation to alterations in chlorophyll metabolism, osmotic adjustment, and accumulation of organic metabolites.

Dichondra (Dichondra repens) is an important ground cover plant for landscaping and establishment of green space, but adaptive mechanism of drought tolerance is not well understood in this species. This study was conducted to compare differential response to drought stress among three genotypes (Dr5, Duliujiang, and Dr29) based on integrated physiological, ultrastructural, and metabolic assays. Results showed that drought significantly inhibited photosynthesis, accelerated lipids peroxidation, and also disrupted water balance and cellular metabolism in dichondra plants. Dr5 showed better photochemical efficiency of photosystem II and water homeostasis, less oxidative damage, and more stable chlorophyll metabolism than Duliujinag or Dr29 in response to drought stress. In addition, Dr5 accumulated more amino acids, organic acids, and other metabolites, which was good for maintaining better antioxidant capacity, osmotic homeostasis, and energy metabolism under drought stress. Drought tolerance of Duliujiang was lower than Dr5, but better than Dr29, which could be positively correlated with accumulations of sucrose, maltitol, aconitic acid, isocitric acid, and shikimic acid due to critical roles of these metabolites in osmotic adjustment and metabolic homeostasis. Current findings provide insights into understanding of underlying mechanism of metabolic regulation in dichondra species. Dr5 could be used as an important drought-tolerant resource for cultivation and water-saving breeding.

Mechanisms Underlying the Differential Sensitivity to Mesotrione in Sweet Corn

Mesotrione is a widely used post-emergence herbicide for maize. The toxicity of mesotrione to maize (especially sweet corn) has been widely reported, and some sweet corn varieties are highly sensitive to mesotrione, which affects subsequent plant growth periods. However, the molecular mechanisms responsible for the differences in susceptibility to mesotrione are not known. By comparing changes in the transcriptome of mesotrione-tolerant line 301 and mesotrione-sensitive line 276 after mesotrione treatment, we found that the genes coding light-harvesting chlorophyll protein complex were induced in 301, and the genes coding loosening cell walls were overrepresented in 276. The net photosynthetic rate, maximum photochemical efficiency of leaf PSII, photochemical quenching of chlorophyll fluorescence, and the electron transport rate were significantly higher in 301 than in 276 after mesotrione treatment, and these effects became more severe as time passed. In addition, oxidative balance was also affected by mesotrione. Compared with 301, SOD, POD, and CAT activities were significantly reduced with longer exposure time in 276. The results suggested that sweet corn can mitigate herbicide mesotrione toxicity by improving photosynthesis, ROS scavenging, and cell wall synthesis.

Hydrogen Sulfide Alleviates Oxidative Damage under Chilling Stress through Mitogen-Activated Protein Kinase in Tomato.

Tomato is the vegetable with the largest greenhouse area in China, and low temperature is one of the main factors affecting tomato growth, yield, and quality. Hydrogen sulfide (H2S) plays an important role in regulating plant chilling tolerance, but its downstream cascade reaction and mechanism remain unclear. Mitogen-activated protein kinases (MAPK/MPKs) are closely related to a variety of signaling substances in stress signal transmission. However, whether H2S is related to the MPK cascade pathway in response to low-temperature stress is rarely reported. In this study, NaHS treatment significantly decreased the electrolyte leakage (EL), superoxide anion (O2-) production rate, and hydrogen peroxide (H2O2) content of seedlings at low temperatures. In addition, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were obviously increased; and the photochemical efficiency of PSII (Fv/Fm) was enhanced with treatment with NaHS, indicating that NaHS improved the seedlings' cold tolerance by alleviating the degree of membrane lipid peroxidation and oxidative damage. However, H2S scavenger hypotaurine (HT) treatment showed the opposite effect. We found that H2S content, L-cysteine desulfhydrase (LCD) activity, and mRNA expression were increased by chilling stress but reduced by MPK inhibitor PD98059; PD98059 reversed the alleviating effect of H2S via increasing the EL and H2O2 contents. The expression levels of MPK1-MPK7 at low temperatures showed that SlMPK4 was significantly induced by exogenous NaHS and showed a trend of first increasing and then decreasing, while the expression level of SlMPK4 in HT-treated seedlings was lower than that of the control. After SlMPK4 was silenced by virus-induced gene silencing, the H2S-induced upregulation of C-repeat-Binding Factor (CBF1), inducer of CBF expression 1 (ICE1), respiratory burst oxidase homologs (RBOH1, RBOH2) at low temperatures disappeared, and tomato cold tolerance decreased. In conclusion, H2S improves the cold tolerance of tomato plants by increasing the activity of antioxidant enzymes and reducing reactive oxygen species (ROS) accumulation and membrane lipid peroxidation. MPK4 may act as a downstream signaling molecule in this process.

Epigallocatechin-3-gallate-induced tolerance to cadmium stress involves increased flavonoid synthesis and nutrient homeostasis in tomato roots

Cadmium (Cd) is a toxic heavy metal, increasingly accumulating in the environment and its presence in various environmental compartments represents a significant risk to human health via the food chain. Epigallocatechin-3-Gallate (EGCG) is a prominent secondary metabolite, which can safeguard plants from biotic and abiotic stress. However, the role of EGCG in flavonoid synthesis, nutrient acquisition and reactive oxygen species (ROS) metabolism under Cd stress remains unclear. Here, we examined the effects of EGCG and Cd treatment on leaf photochemical efficiency, cell ultrastructure, essential element acquisition, antioxidant system, and secondary metabolism in tomato (Solanum lycopersicum L.). The results showed that O2•−, H2O2, and malondialdehyde levels increased after Cd treatment, but Fv/Fm decreased significantly, suggesting that Cd induced oxidative stress and photoinhibition. However, EGCG mitigated the adverse effects of Cd-induced phytotoxicity in both the roots and leaves. A decrease in ROS accumulation under EGCG + Cd treatment was mainly attributed to the significant enhancement in antioxidant enzyme activity, flavonoid content, and PHENYLALANINE AMMONIA-LYASE expression in roots. Moreover, EGCG reduced Cd content but increased some essential nutrient contents in tomato plants. Transmission electron microscopy-based observations revealed that EGCG treatment safeguards leaf and root cell ultrastructure under Cd stress. This implies that tomato plants subjected to Cd stress experienced advantageous effects upon receiving EGCG treatment. The present work elucidated critical mechanisms by which EGCG induces tolerance to Cd, thereby providing a basis for future investigations into environmentally sustainable agricultural practices in areas contaminated with heavy metals, for utilizing naturally occurring substances found in plants.