Quantum Yield Of PSII Photochemistry Research Articles

Exogenous hydrogen sulfide increased Nicotiana tabacum L. resistance against drought by the improved photosynthesis and antioxidant system

Drought stress is an abiotic stressor that impacts photosynthesis, plant growth, and development, leading to decreased crop yields. Sodium hydrosulfide (NaHS), an exogenous additive, has demonstrated potential regulatory effects on plant responses to polyethylene glycol-induced drought stress in tobacco seedlings. Compared to the control, drought stress induced by 15 g/L PEG-6000 significantly reduced several parameters in tobacco seedlings: shoot dry weight (22.83%), net photosynthesis (37.55%), stomatal conductance (33.56%), maximum quantum yield of PSII (Fv/Fm) (11.31%), photochemical quantum yield of PSII (ΦPSII) (25.51%), and photochemical quenching (qP) (18.17%). However, applying NaHS, an H2S donor, mitigated these effects, ultimately enhancing photosynthetic performance in tobacco seedlings. Furthermore, optimal NaHS concentration (0.4 mM) effectively increased leaf stomatal aperture, relative water content (RWC) and root activity, as well as facilitated the absorption of N, K, Mg and S. It also enhanced the accumulation of soluble sugar and proline content to maintain osmotic pressure balance under drought stress. Compared to drought alone, pretreatment with NaHS also bolstered the antioxidant defense system in leaves, leading to 22.93% decrease in hydrogen peroxide (H2O2) content, a 22.19% decrease in malondialdehyde (MDA) content and increased activities of ascorbate peroxidase (APX) by 28.13%, superoxide dismutase (SOD) by 17.07%, peroxidase (POD) by 46.99%, and catalase (CAT) by 65.27%. Consequently, NaHS protected chloroplast structure and attenuated chlorophyll degradation, thus mitigating severe oxidative damage. Moreover, NaHS elevated endogenous H2S levels, influencing abscisic acid (ABA) synthesis and the expression of receptor-related genes, collaboratively participating in the response to drought stress. Overall, our findings provide valuable insights into exogenous NaHS’s role in enhancing tobacco drought tolerance. These results lay the foundation for further research utilizing H2S-based treatments to improve crop resilience to water deficit conditions.

The Physiological Response of Salix matsudana for Water Pollution by 2,4-Dinitrophenol.

In this study, the effects of different concentrations of 2,4-dinitrophenol (2,4-DNP) stress on physiological parameters, as well as the uptake and removal of 2,4-DNP in Salix matsudana, were investigated using hydroponic simulation experiments to explore the potential of the use of Salix matsudana in the phytoremediation of wastewater polluted by 2,4-DNP. The results showed that PN (net photosynthetic rate), Tr (transpiration rate), Gs (stomatal conductance), Ls (stomatal limitation value), Fv/Fm (maximal quantum yield of PSII photochemistry), and qp (photochemical quenching coefficient) of Salix matsudana seedlings showed an overall decreasing trend, while Ci (intercellular CO2 concentration) showed an increasing trend with the increase in 2,4-DNP concentration. The net photosynthetic rate and intercellular carbon dioxide concentration showed an opposite trend in the leaves with the increase in 2,4-DNP stress concentration, and the inhibition of net photosynthesis by 2,4-DNP on Salix matsudana seedlings was mainly based on non-stomatal factors. In the 15 d incubation experiment, the values of SOD (superoxide dismutase), POD (peroxidase), and CAT (catalase) indexes were higher at low concentrations of 2,4-DNP stress, and all three enzymes reached their maximum values at 10 mg L-1 of 2,4-DNP and then decreased. Salix matsudana seedlings could tolerate 2,4-DNP stress well, which did not exceed 20 mg L-1. The toxicity of 2,4-DNP solution was significantly reduced after purification by Salix matsudana seedlings. The removal rate of 2,4-DNP was higher than 80% in each treatment group by Salix matsudana purified after 15 days. When the concentration of 2,4-DNP reached 20 mg L-1, the contents of MDA (malonicdialdehyde) were 55.62 mmol g-1, and the values of REC (relative conductivity) and LD (leaf damage) were 63.51% and 59.93%, respectively. The structure and function of the cell membrane in leaves were seriously damaged. With the increase in 2,4-DNP concentration, the removal of 2,4-DNP by Salix matsudana seedlings showed a decreasing trend. When the 2,4-DNP concentration was 5 mg L-1, the highest removal rate of 2,4-DNP by Salix matsudana seedlings was 95.98%, while when the 2,4-DNP concentration was 20 mg L-1, the highest removal rate was 86.76%. It is noted that the suitable, recommended concentration for the phytoremediation of 2,4-DNP contamination by Salix matsudana seedlings is between 8.81 and 13.78 mg L-1.

Optimized irrigation practices with fertilizer utilization strategies to improve photo-fluorescence efficiency, vascular bundles and maize production in semi-arid regions

The mechanism of irrigation models combined with fertilizer utilization strategies under the biodegradable film mulching could greatly promote crop photosynthesis, vascular bundles structure; resource utilization and maize production are unclear in semi-arid areas. Unfortunately, this mechanism provides a scientific basis for improving irrigation and fertilizer utilization. A field study was carried out during 2021–2022 years. Seven treatments were established: two nitrogen levels: low-N (150 kg N ha−1) and high-N (300 kg N ha−1) combined with three different irrigation models: drip irrigation (DI), ridge irrigation (RI) and border irrigation (BI) under the biodegradable film mulching with (CK) treatment have no irrigation, fertilizer and mulching. Our results revealed that DIH treatment considerably increased soil water storage, enhanced photosynthesis rate (Pn) of maize by mainly to facilitate stomatal opening compared to the rest of all treatments. In addition, it also enhances the differentiation of the vascular bundle system and maintains its post silk function under better environmental conditions, greatly improving nitrogen storage in soil and plants, and enhancing maize productivity. DIH and RIH treatments significantly increased net photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), maximum quantum yield of PSII photochemistry (Fv/Fm), and effective quantum yield of PSII photochemistry (ΦPSII), photochemical quenching (qP), non-photochemical quenching (NPQ), and yield were observed, but evapotranspiration (ET) decreased at different growth stages. The results showed that DIH treatment was an effective tillage strategy, which increased biomass yield by 32.6 %, grain yield by 46.0 %, water use efficiency (WUE) by 46.2 %, and nitrogen use efficiency (NUE) by 86.4 % compared to other treatments. Given these results, thus we recommend the drip irrigation combined with a high-N level under a biodegradable film mulching increase photo-fluorescence efficiency, maize production and resource utilization efficiency in semi-arid regions.

Photosynthetic Performance and Heterogeneous Anatomical Structure in Prunus humilis under Saline–Alkaline Stress

Prunus (P.) humilis is a small woody shrub that has been widely planted in northern China due to its high nutritional value and resistance to environmental abiotic stress. However, little information about the responses of photosynthetic performance and the anatomical structure of P. humilis to saline–alkaline stress (SAS) under field conditions is available. Here, we investigated the behavior of the photosynthetic apparatus of P. humilis by measuring the chlorophyll fluorescence parameters under moderate (MS) and severe (SS) saline–alkaline stress and analyzing their relationship to leaf anatomical traits. The results showed that SAS significantly decreased the net photosynthetic rate (An) but increased the substomatal CO2 concentration (Ci). The maximum photochemical quantum yield of PSII (Fv/Fm) and the efficient quantum yield of PSII [Y(II)] decreased under MS and SS conditions, and this decrease was greater in the distal (tip) than in the proximal (base) leaf. Compared to the leaf tip, the base of P. humilis leaves seemed to have a stronger ability to cope with MS, as was made evident by the increased quantum yield of regulated energy dissipation in PSII [Y(NPQ)] and decreased excitation pressure (1-qP). Under MS and SS conditions, the shapes of the chlorophyll a fluorescence transient (OJIP) changed markedly, accompanied by decreased PSII acceptor-side and donor-side activities. The palisade–spongy tissue ratio (PT/ST) increased significantly with increasing stress and showed a significant correlation with the chlorophyll fluorescence parameters in the leaf base. These results suggested that the activity of PSII electron transfer in the upper leaf position tended to be more sensitive to saline–alkaline stress, and a chlorophyll fluorescence analysis proved to be a good technique to monitor impacts of saline–alkaline stress on photosynthetic function, which may reflect the non-uniformity of leaf anatomy. In addition, among the anatomical structure parameters, the palisade–spongy tissue ratio (PT/ST) can be used as a sensitive indicator to reflect the non-uniform of photosynthetic function and leaf anatomy under stress.

A novel eco-friendly approach of combining vermicompost and effective microorganisms sustains wheat (Triticum aestivum L.) drought tolerance by modulating photosynthetic performance and nutrient acquisition

The most significant threat to global food security is water scarcity. Despite the fact that vermicompost (an effective organic fertilizer rich in humic substances, macro- and micro-nutrients, earthworm excretions, beneficial soil microbes, plant growth hormones, enzymes) and effective microorganisms (EM; photosynthetic bacteria, lactic acid bacteria, yeasts, actinomycetes, fermenting fungi) have been recognized as powerful strategies for alleviating environmental stresses, their combined effect has not been studied. Herein, as a first investigation, we aimed to enhance wheat’s drought tolerance using an eco-friendly approach that combined vermicompost and EM. The study employed twelve treatments in a completely randomized design. The treatments included control, as well as single and combined applications of vermicompost and EM at three different irrigation levels (100%, 70%, and 30% of field capacity). Vermicompost and EM, applied singly or in combination, ameliorated drought-induced reduction in wheat growth and productivity by elevating photosynthetic pigment content, photochemical processes, Calvin cycle enzyme activity, net photosynthetic rate, transpiration rate, stomatal conductance, maximum quantum efficiency of PSII photochemistry, actual photochemical efficiency of PSII, electron transport rate, photochemical quenching coefficient, and effective quantum yield of PSII photochemistry. Additionally, adding vermicompost and/or EM improved wheat drought tolerance by increasing nutrient (nitrogen, phosphorus, potassium, iron, zinc, copper) acquisition, roots’ ATP content, H+-pump activity, and membrane stability index while lowering hydrogen peroxide content, lipid peroxidation, and electrolyte leakage. The new evidence demonstrates that combining vermicompost with EM sustains wheat drought tolerance by regulating photosynthetic efficiency, nutrient acquisition, root H+-pump activity, and membrane stability. Overall, utilizing vermicompost/EM is a novel approach to improving plant physiological responses and overcoming drought-related challenges.

Residues from the Fundão Dam Accident in Brazil and their Effects on Photosynthetic Efficiency of Two Restinga Plant Species.

In 2015, a breach in the Fundão Dam in Mariana (Minas Gerais State, Brazil) resulted in the release of contaminated tailings into the Doce River basin. This accident increased the concentrations of arsenic (As), lead (Pb), cadmium (Cd), vanadium (V), and manganese (Mn) in the soil, posing a potential hazard to the physiology of native species. The purpose of this study was to assess whether chlorophyll a fluorescence (ChlF) in Allagoptera arenaria and Guapira pernambucensis changed following this accident when tested under different precipitation regimes in relation to soil properties and metal(loid) absorption. Our research was conducted in two sites located in the state of Espírito Santo in southeastern Brazil. Five independent biological replicates of A. arenaria and G. pernambucensis were selected at each site for nutritional and chlorophyll a fluorescence analysis. Five years after the dam rupture, A. arenaria and G. pernambucensis had absorbed As, Pb, and V. The increased amounts of metal(loid)s absorbed did not significantly impair the OJIP curve configuration for either species during the evaluated periods. However, A. arenaria at Biological Reserve of Comboios (RBC) during the rainy season showed increases in the values of maximum quantum yield of PSII photochemistry (φP0) and total performance index on absorption basis (PITOTAL). These changes indicated more efficient tolerance mechanisms for increases in the concentrations of As, Pb, and V than those observed in G. pernambucensis. It was concluded that A. arenaria and G. pernambucensis exhibited an acclimation strategy in response to increased absorption of metal(loid)s.

The Influence of Varying Wavelengths of LED Light on the Development, Physiology Response, and Metabolism Activities of Micropropagated Dendrobium Hybrid ‘Shuijing’ Plantlets

Dendrobium hybrids have a significant role in the present floral sector. The aim of this research was to evaluate how various light qualities affect the physiological and biochemical traits of Dendrobium ‘Shuijing’. In order to determine the optimal light quality for in vitro cultivation of Dendrobium plantlets, we examined the correlations between growth, antioxidant capacity, and nutrient and chlorophyll levels, as well as chlorophyll fluorescence. The growth rate was compared by using different light qualities emitted by the LED light source. These included red light (R), blue light (B), and three ratios: 8R:2B, 7R:3B, and equal proportions of both colors, known as white, fluorescent light (CK). The combination of 7R:3B resulted in noticeable enhancements in leaf count, root length, root activity, fresh and dry weight measurements, antioxidant capability, as well as chlorophyll content and fluorescence. Specifically, the mixture of red and blue LED lights at a ratio of 7R:3B led to increased leaf number, root length, root activity, fresh and dry weight measurements, antioxidant ability, and chlorophyll content with improved fluorescence. In order to explore the effect of light quality on the growth and development of Dendrobium, the chlorophyll content and chlorophyll fluorescence parameters of plants under all light quality conditions were analyzed by using a linear regression model with other physiological and biochemical indexes. A significant correlation between non-photochemical quenching (NPQ) and leaf length was also observed. The content of chlorophyll b showed significant correlations with both root number and leaf number. Furthermore, chlorophyll a, along with its ratio to chlorophyll b, significantly correlated with root length. Chlorophyll b and the relative electron transport rate of PSII (ETRII) significantly correlated with root activity and the free proline content (FPC) and catalase (CAT) activity. The photochemical quenching coefficient (qP) significantly correlated with total soluble sugars content (SSC) and peroxidase (POD) activity. The correlation between the quantum yield of PSII (Fv/Fm ratio) and superoxide dismutase (SOD) activity was found to be significant. Similarly, the effective quantum yield of PSII photochemistry (ΦPSII) showed significant correlations with fresh weight, dry weight, soluble protein content (SPC), and ascorbate peroxidase (APX) activity. Through a principal component analysis (PCA), it was observed that plants cultivated under the 7R:3B light treatment achieved significantly better comprehensive scores compared to those grown under different light treatments. In conclusion, growth achieved under an LED emitting a ratio of 7R:3B light yielded the most robust Dendrobium hybrid plantlets within a controlled environment.

Chlorophyll fluorescence in sentinel plants for the surveillance of chemical risk

This research aimed to develop natural plant systems to serve as biological sentinels for the detection of organophosphate pesticides in the environment. The working hypothesis was that the presence of the pesticide in the environment caused changes in the content of pigments and in the photosynthetic functioning of the plant, which could be evaluated non-destructively through the analysis of reflected light and emitted fluorescence. The objective of the research was to furnish in vivo indicators derived from spectroscopic parameters, serving as early alert signals for the presence of organophosphates in the environment. In this context, the effects of two pesticides, Chlorpyrifos and Dimethoate, on the spectroscopic properties of aquatic plants (Vallisneria nana and Spathyfillum wallisii) were studied. Chlorophyll-a variable fluorescence allowed monitoring both pesticides' presence before any damage was observed at the naked eye, with the analysis of the fast transient (OJIP curve) proving more responsive than Kautsky kinetics, steady-state fluorescence, or reflectance measurements. Pesticides produced a decrease in the maximum quantum yield of PSII photochemistry, in the proportion of PSII photochemical deexcitation relative to PSII non photochemical decay and in the probability that trapped excitons moved electrons into the photosynthetic transport chain beyond QA−. Additionally, an increase in the proportion of absorbed energy being dissipated as heat rather than being utilized in the photosynthetic process, was notorious. The pesticides induced a higher deactivation of chlorophyll excited states by photophysical pathways (including fluorescence) with a decrease in the quantum yields of photosystem II and heat dissipation by non-photochemical quenching. The investigated aquatic plants served as sentinels for the presence of pesticides in the environment, with the alert signal starting within the first milliseconds of electronic transport in the photosynthetic chain. Organophosphates damage animals' central nervous systems similarly to certain compounds found in chemical weapons, thus raising the possibility that sentinel plants could potentially signal the presence of such weapons.

Effects of nitrogen addition and Bothriochloa ischaemum and Lespedeza davurica mixture on plant chlorophyll fluorescence and community production in semi-arid grassland.

Grass-legume mixture can effectively improve productivity and stimulate overyielding in artificial grasslands, but may be N-limited in semi-arid regions. This study investigated the effects of N addition on chlorophyll fluorescence and production in the grass-legume mixtures community. An N addition experiment was conducted in the Bothriochloa ischaemum and Lespedeza davurica mixture community, with seven mixture ratios (B0L10, B2L8, B4L6, B5L5, B6L4, B8L2, and B10L0) according to the sowing abundance of B.ischaemum and L.davurica and four N addition levels, N0, N25, N50, and N75 (0,25,50,75kgNhm-2 a-1), respectively. We analyzed the response of chlorophyll fluorescence parameters of the two species, the rapid light-response curves of chlorophyll fluorescence, as well as aboveground biomass (AGB) and overyielding. Our results showed that the two species showed different photosynthetic strategies, with L.davurica having significantly higher initial fluorescence (Fo), effective photochemical quantum yield of PSII (ΦPSII), and coefficient of photochemical fluorescence quenching (qP) than B. ischaemum, consisting with results of rapid light-response curves. N addition and mixture ratio both had significant effects on chlorophyll fluorescence and AGB (p<0.001). The ΦPSII and qP of L.davurica were significantly lowest in B5L5 and B6L4 under N addition, and the effect of N varied with mixture ratio. The photosynthetic efficiency of B. ischaemum was higher in mixture than in monoculture (B10L0), and ΦPSII was significantly higher in N50 than in N25 and N50 at mixture communities except at B5L5. The community AGB was significantly higher in mixture communities than in two monocultures and highest at B6L4. In the same mixture ratio, the AGB was highest under the N50. The overyielding effects were significantly highest under the N75 and B6L4 treatments, mainly attributed to L.davurica. The partial least squares path models demonstrated that adding N increased soil nutrient content, and complementary utilization by B.ischaemum and L.davurica increased the photosynthetic efficiency. However, as the different photosynthetic strategies of these two species, the effect on AGB was offset, and the mixture ratio's effects were larger than N. Our results proposed the B6L4 and N50 treatments were the optimal combination, with the highest AGB and overyielding, moderate grass-legume ratio, optimal community structure, and forage values.

Soil drought stress and high-temperature effects on photosystem II in different juvenile spruce provenances

Abstract With prolonged periods of drought and temperature extremes becoming more frequent, the stress on Norway spruce has increased, as its ecological optimum is in colder and more humid environments. However, it is a tree species with a good adaptability, due to its great geographic and intraspecific variability. In this study, we tested the sensitivity of chlorophyll a fluorescence tools for the early detection of drought and heat stress, as well as their combined effect, in four Slovak Carpathian provenances, under controlled laboratory conditions. Responses in photosynthetic parameters of fast and slow (light response curves) kinetics of chlorophyll a fluorescence were analysed in spruce seedlings under four treatments: control, drought, heat, and combined drought + heat. Heat and drought + heat stresses led to the decrease of photosynthetic efficiency to a greater extent than in the case of only individual drought stress. The less sensitive parameter impacted by the stresses was the maximum quantum yield of PSII photochemistry (Fv/Fm), while the more sensitive parameters were: the performance index based on absorption of light energy (PIABS), the effective quantum yield of the PSII (ΦPSII), and the coefficients of non-photochemical fluorescence quenching (NPQ, qN). The significant variability in responses of individual provenances was also observed. Seedlings from two studied provenances responded better to these abiotic stresses (Pa-680 and Pa-1500); however, Pa-1500 provenance from the highest altitude showed the best ability of resistance to soil drought stress, as well as to high temperature effect. This rapid screening of photosystems II efficiency showed the importance of the selection of more resistant populations to concurrent stresses as one of the measures to mitigate climate change impacts.

Proline priming: An efficient strategy to mitigate salinity impact at early developmental stages of the oilseed halophyte Cakile maritima

Seed germination is a vital process, yet extremely sensitive to salinity. This is particularly true for coastal halophytes like the annual oilseed species Cakile maritima, which faces the simultaneous impact of wind, salt-spray and seawater inundations in its natural biotopes. At the early developmental stages, this may jeopardize seed germination, plant establishment capacity and hence its development and persistence. Osmopriming is a pre-sowing approach aiming to improve seedling emergence and establishment in adverse environments. Here, we investigate the effect of proline (at 0, 1, 5, and 20 mM) pre-treatment on salt tolerance of C. maritima at the juvenile stage under salinity (0, 100, and 200 mM NaCl). Proline seed priming enhanced the germination rate (28% to 92%) and promoted seedling establishment of C. maritima by stimulating α-amylase activity even at the highest salinity (+55 %). Besides, after transfer of non-germinated seeds on distilled water, salt impact was fully reversible. At the seedling stage, chlorophyll fluorescence parameters showed that this osmoticum increased the maximal quantum yield of PSII photochemistry (Fv/Fm) and the quantum yield of photochemical energy conversion [Y(II)]. In contrast, the quantum yield of nonregulated nonphotochemical energy dissipation [Y(NO)] and the quantum yield of regulated nonphotochemical energy dissipation [Y(NPQ)], which might be correlated to the mitigation of the salt deleterious effects on PSII. Proline and carbohydrate concentrations also increased following priming. Overall, our data provide strong arguments for using proline at low doses (1 and 5 mM) as a successful priming agent to alleviate salinity-induced adverse effect on plants.

Impact of exogenous melatonin foliar application on physiology and fruit quality of wine grapes (Vitis vinifera) under salt stress.

Soil salinisation is an important abiotic stress faced in grape cultivating, leading to weakened plant vigour and reduced fruit quality. Melatonin as a novel hormone has shown positive exogenous application value. Therefore, this study used wine grape (Vitis vinifera ) 'Pinot Noir' as a test material to investigate the changes of foliar spraying with different concentrations of melatonin on the physiology and fruit quality of wine grapes in a field under simulated salt stress (200mmolL-1 NaCl). The results showed that foliar spraying of melatonin significantly increased the intercellular CO2 concentration, maximum photochemical quantum yield of PSII, relative chlorophyll and ascorbic acid content of the leaves, as well as the single spike weight, 100-grain weight, transverse and longitudinal diameters, malic acid, α-amino nitrogen and ammonia content of fruits, and decreased the initial fluorescence value of leaves, ascorbate peroxidase activity, glutathione content, fruit transverse to longitudinal ratio and tartaric acid content of plants under salt stress. Results of the comprehensive evaluation of the affiliation function indicated that 100μmolL-1 melatonin treatment had the best effect on reducing salt stress in grapes. In summary, melatonin application could enhance the salt tolerance of grapes by improving the photosynthetic capacity of grape plants under salt stress and promoting fruit development and quality formation, and these results provide new insights into the involvement of melatonin in the improvement of salt tolerance in crop, as well as some theoretical basis for the development and industrialisation of stress-resistant cultivation techniques for wine grapes.

The responses of pepper plants to nitrogen form and dissolved oxygen concentration of nutrient solution in hydroponics

BackgroundThe presence of oxygen in the growth medium is absolutely essential for root development and the overall metabolic processes of plants. When plants do not have an adequate oxygen supply for respiration, they can experience a condition known as hypoxia. In order to investigate the impact of different nitrogen forms and varying oxygen levels in nutrient solutions on the growth, photosynthesis, and chlorophyll fluorescence parameters of bell pepper plants, a comprehensive study was conducted. The experiment was designed as a factorial experiment, considering two main factors: nitrogen forms (calcium nitrate and ammonium sulfate) with a fixed nitrogen concentration of 5 mM, and the oxygen levels of the nutrient solutions (ranging from 1.8 ± 0.2 to 5.3 ± 0.2 mg. L-1).ResultsThe study examined the effects of nitrogen (NH4+ and NO3−) application on various parameters of vegetative growth. The results demonstrated that the use of ammonium (NH4+) led to a reduction in the most measured parameters, including the fresh and dry mass of both the root and shoot, at low O2 concentrations of 1.8 ± 0.2; 2.6 ± 0.2 and 3.8 ± 0.2 mg. L-1. However, an interesting observation was made regarding the impact of oxygen levels on root growth in plants grown with nitrate (NO3−). Specifically, the highest levels of oxygen significantly increased root growth in NO3−-fed plants. Additionally, the application of NH4+ resulted in an increase in chlorophyll concentration in the leaves, particularly when combined with high oxygen levels in the nutrient solution. On the other hand, leaves of plants fed with NO3− exhibited higher photosynthetic rate (A), intrinsic water use efficiency (iWUE), and instantaneous carboxylation efficiency (A/Ci) compared to those fed with NH4+. Furthermore, it was found that NO3−-fed plants displayed the highest instantaneous carboxylation efficiency at oxygen levels of 3.8 and 5.3 mg. L-1, while the lowest efficiency was observed at oxygen levels of 1.8 and 2.6 mg. L-1. In contrast, NH4+-grown plants exhibited a higher maximal quantum yield of PSII photochemistry (Fv/Fm), as well as increased variable fluorescence (Fv) and maximum fluorescence (Fm), compared to NO3−-grown plants. Interestingly, the NO3−-fed plants showed an increase in Fv/Fm, Fv, and Fm with the elevation of oxygen concentration in the nutrient solution up to 5.3 mg. L-1.ConclusionThis study showed that, the growth and photosynthesis parameters in bell pepper plants are sensitive to oxygen stress in floating hydroponic culture. Therefore, the oxygen level in the nutrient solution must not be lower than 3.8 and 5.3 mg. L-1 in NH4+ and NO3− –supplied culture media or nutrient solutions, respectively.

Soil water availability modulates the response of grapevine leaf gas exchange and PSII traits to a simulated heat wave

Background and aimsA better understanding of plant carbon assimilation, water status and photosystem performance responses to combined heat and drought stress would help to optimize grapevine management under such limiting conditions.MethodsGas exchange and chlorophyll fluorescence parameters were measured in potted grapevines, cv Sauvignon Blanc, before, during and after simulated six-day heat (Tmax = 40 °C) wave using heated well-watered (HW), heated drought-stressed (HD), non-heated well-watered (CW) and non-heated dry (CD) vines.ResultsPhotosynthesis and stomatal conductance in HW vines increased during the morning and dropped in the afternoon with respect to CW vines. Daily plant transpiration in HW almost doubled that of CW vines. When grapevines were already exposed to drought, the effects of the heat wave were negligible, with HD plants showing similar leaf photosynthesis and transpiration to their CD counterparts. Heat, but not drought stress, decreased the maximum (Fv/Fm) and effective photochemical quantum yield of PSII (φPSII), and also affected the use of absorbed energy. HW plants dissipated more radiative energy as heat, a protective mechanism of the photosystem, while HD vines increased the energy dissipated by non-regulated non-photochemical pathways, which might lead to photoinhibition damages. The different behavior could be due to the enhanced transpiration rate and consequent decrease in leaf temperature in HW as compared to HD vines. After the heat wave, only HW vines recovered the afternoon values of photosynthesis, stomatal conductance and φPSII to similar levels as those in CW vines.ConclusionDrought had a more significant effect than heat stress on photosynthesis, stomatal conductance and transpiration. The combined heat and drought stress, however, increased the proportion of energy lost by the leaves through harmful non-regulated dissipative pathways. With adequate soil water availability, grapevines withstood the heat wave period through an increase in leaf transpiration, which decreased leaf temperature and protected the PSII from heat damage.

Changes in Photosynthetic Characteristics between Green-Leaf Poplar Linn. "2025" and Its Bud-Sporting Colored-Leaf Cultivars.

Colored-leaf poplar is increasingly popular due to its great ornamental values and application prospects. However, the photosynthetic characteristics of these colored-leaf cultivars have not been well understood. In this study, the photosynthetic differences between green-leaf poplar Populus deltoids Linn. "2025" (L2025) and colored-leaf cultivars 'Zhonghong poplar' (ZHP), 'Quanhong poplar' (QHP), and 'Caihong poplar' (CHP) were investigated on several levels, including chloroplast ultrastructure observation, photosynthetic physiological characteristics, and expression analysis of key genes. The results showed that the photosynthetic performance of ZHP was basically consistent with that of L2025, while the ranges of light energy absorption and efficiency of light energy utilization decreased to different degrees in CHP and QHP. A relatively low water use efficiency and high dark respiration rate were observed in QHP, suggesting a relatively weak environmental adaptability. The differences in chloroplast structure in different colored-leaf poplars were further observed by transmission electron microscopy. The disorganization of thylakoid in CHP was considered an important reason, resulting in a significant decrease in chlorophyll content compared with other poplar cultivars. Interestingly, CHP exhibited extremely high photosynthetic electron transport activity and photochemical efficiency, which were conductive to maintaining its relatively high photosynthetic performance. The actual quantum yield of PSII photochemistry of ZHP was basically the same as that of QHP, while the relatively high photosynthetic performance indexes in ZHP suggested a more optimized photosynthetic apparatus, which was crucial for the improvement of photosynthetic efficiency. The differential expressions of a series of key genes in different colored-leaf poplars provided a reasonable explanation for anthocyanin accumulation and specific photosynthetic processes.

Effects of Exogenous Melatonin on the Growth and Physiological Characteristics of Ginkgo biloba L. under Salinity Stress Conditions

Ginkgo (Ginkgo biloba L.) is a cherished relic among plants, commonly planted as a street tree. However, it faces cultivation challenges due to escalating soil salinization and widespread snowmelt application. Therefore, this study used 4-year-old Ginkgo seedlings to investigate how exogenous melatonin at varying concentrations affects seedling growth and physiology under salinity stress. The results revealed that appropriate melatonin concentrations (0.02, 0.1 mmol·L−1) significantly mitigated leaf yellowing under different NaCl stress levels. Furthermore, they increased ground diameter, current-year branch growth, relative water concentration, free proline, and soluble sugars in leaves. Melatonin also reduced electrolyte exudation rates, flavonoids, and malonic dialdehyde concentration, while enhancing peroxidase and superoxide dismutase activities. This led to reduced chlorophyll content, photosynthetic rate, stomatal conductance, and transpiration rate, stabilizing intercellular CO2 concentration, preserving photosynthetic structures, and enhancing photosynthetic rates. Additionally, the decline in the photosynthetic electron transport rate, the effective photochemical quantum yield of PSII, and the potential efficiency of primary conversion of light energy of PSII was alleviated. Minimal fluorescence and the non-photochemical quenching coefficient also improved. However, high melatonin concentration (0.5 mmol·L−1) exacerbated salinity stress. After analyzing composite scores, the 0.02 mmol·L−1 melatonin treatment was most effective in alleviating NaCl stress, while the 0.5 mmol·L−1 treatment intensified physiological stress under 200 mmol·L−1 NaCl stress. Principal component analysis and correlation analysis identified seven physiological indicators (photosynthetic rate, transpiration rate, photosynthetic electron transport rate, minimal fluorescence, superoxide dismutase, free proline, and chlorophyll a) and three growth indicators (ground diameter, branch length, and current-year branch thickness) as key markers for rapid salinity stress assessment in Ginkgo. These findings are crucial for addressing challenges associated with snowmelt’s impact on roadside Ginkgo trees, expanding planting areas, and breeding exceptional salt-tolerant Ginkgo varieties.

Morphology, photosynthetic and molecular mechanisms associated with powdery mildew resistance in Kentucky bluegrass.

Kentucky bluegrass (Poa pratensis L.), one of the most widely used cool-season turfgrasses around the world, is sensitive to powdery mildew (PM; Blumeria graminis). The PM strain identification and regulation mechanisms of Kentucky bluegrass in response to pathogens still remain unclear. Through morphological and molecular analyses, we identified that the pathogen in Kentucky bluegrass was B. graminis f. sp. poae. The infection of B. graminis led to a reduction of the sclerenchyma area, expansion of vesicular cells and movement of chloroplasts. The infected leaves had significantly lower values in net photosynthesis, stomatal conductance and transpiration rate, maximal quantum yield of PSII photochemistry, photochemical quenching and non-regulated energy dissipation compared to mock-inoculated leaves. Expressions of light-harvesting antenna protein genes LHCA and LHCB and photosynthetic electron transport genes petE and petH decreased significantly in infected leaves. Furthermore, upregulations of genes involved in plant-pathogen interaction, such as HSP90, RBOH, and RPM and downregulations of EDS, RPS and WRKY were observed in infected leaves. The findings may help design a feasible approach to effectively control the PM disease in Kentucky bluegrass and other related perennial grass species.

Yeast Solution Spray and Ozone Gas Fumigation as Methods of Protecting Tomato Plants Against Diseases

Abstract The aim of the study was to determine the effect of ozone fumigation and spraying with microorganisms, i.e. yeast, on selected physiological parameters, and the extent of disease infection of tomato plants. Tomato plants were grown in the ground under covers. Throughout the 2021 and 2022 growing season, the plants were exposed to variable factors, i.e. fumigation with gaseous ozone at a dose of 2 ppm for 1 minute and spraying with yeast. After ozonation and spraying with yeast, physiological measurements were made on tomato plants, such as: selected parameters of chlorophyll fluorescence (maximum quantum yield of PSII photochemistry, maximum quantum yield of primary photochemistry) and gas exchange parameters (transpiration rate, stomatal conductivity and intercellular CO2 concentration). In addition, the content of chlorophyll using the SPAD method as well as plant infection by diseases was determined. Compared to the control sample, ozonation resulted in a slight decrease in the physiological parameters of tomato plants. In addition, no visible leaf damage was observed after the ozone gas fumigation process. However, the use of microorganisms did not significantly change the examined physiological parameters. Both after the application of gaseous ozone and microorganisms, a significant impact of the tested variable factors was found on reducing the infection of tomato plants by diseases such as: tomato late blight, tomato alter-nariosis, gray mold, bacterial canker of tomato and bacterial spot of tomato.

Combined effect of fungicide, herbicide and plant elicitor used in apple orchards on non-target epiphytic moss Hypnum cupressiforme

Apple production is a dynamic agricultural system in which pesticides are applied recurrently to control pests and diseases in the orchards. Understanding the impact of such agents on non-target organisms is crucial to minimise unintended consequences while maintaining their use in crop protection. The aim was to test how fungicide, herbicide, elicitor, and their combinations affect the physiology of the epiphytic moss Hypnum cupressiforme that naturally occurs in orchards. Our results showed that both dodine and diflufenican applied separately had a strong negative effect on moss physiology reflected in significantly decreased photosynthetic pigment contents, maximum quantum yield of PSII photochemistry, cell membrane integrity and dehydrogenase activity, and increased membrane lipid peroxidation, which indicates a high physiological stress. Furthermore, the combined use of herbicide and fungicide resulted in further deterioration of the physiological condition compared to the effects of both agents used separately. In many cases, the application of chitosan together with a diflufenican or dodine resulted in a reduction of the negative effects triggered by these agents. The compensatory effect was particularly pronounced in maintaining a low level of cell membrane permeability. Consequently, it can be concluded that chitosan could have a protective function against cell membrane damage in non-target mosses.

Exposure to pentachlorophenol destructs the symbiotic relationship between zooxanthellae and host and induces pathema in coral Porites lutea

Stress from chemical pollutants is among the key issues that have adverse impacts on coral reefs. As a persistent organic pollutant, pentachlorophenol (PCP) has been detected in the seawater of Weizhou Island and was proved to have significant adverse effects on aquatic animals. However, little is known about its effects on scleractinian coral. Therefore, we investigated the response of the coral Porites lutea to PCP stress. Coral bleaching, photosynthesis parameters and antioxidant enzyme activities of P. lutea under PCP exposure were documented. After 96 h of exposure, significant tissue loss and bleaching occurred when the PCP concentration exceeded 100 μg/L. The density of symbiotic zooxanthellae decreased from 2.06 × 106 cells/cm2 to 0.93 × 106 cells/cm2 when the PCP concentration increased from 1 μg/L- 1000 μg/L. Long-term exposure of 120 days to PCP at 0.1 μg/L also led to coral bleaching, the maximum photochemical quantum yield of PSII in P. lutea nubbins significantly decreased to 0.482. The analysis of microbial community distribution indicated that the increase of the pathogenic bacterium Citrobacter may be one of the inducers of coral bleaching. Conjoint analysis of transcriptomics and proteomics showed that the metabolism of amino acids and carbohydrates in zooxanthellae was abnormal, leading to the destruction of its symbiotic relationship with the host. The immune system of the host was disrupted, which could be linked to the prevalence of coral pathema. The toxic responses of PCP on both zooxanthellae and its host were further confirmed by the upregulation of the differential metabolites including 1-naphthylamine and phosphatidylcholine, etc.