Chlorophyll Fluorescence Parameters Research Articles

Construction of Freezing Injury Grade Index for Nanfeng Tangerine Plants Based on Physiological and Biochemical Parameters

Low-temperature freezing stress constitutes the most significant meteorological disaster during the overwintering period in the Nanfeng Tangerine (NT) production area, severely impacting the normal growth and development of the plants. Currently, the accuracy of meteorological disaster warnings and forecasts for NT orchards remains suboptimal, primarily due to the absence of quantitative meteorological indicators for low-temperature freezing stress. Therefore, this study employed NT plants as experimental subjects and conducted controlled treatment experiments under varying intensities of low-temperature freezing stress (0 °C, −2 °C, −5 °C, −7 °C, and −9 °C) and durations (1 h, 4 h, and 7 h). Subsequently, physiological and biochemical parameters were measured, including photosynthetic parameters, chlorophyll fluorescence parameters, reactive oxygen species, osmoregulatory substances, and antioxidant enzyme activities in NT plants. The results demonstrated that low-temperature freezing stress adversely affected the photosynthetic system of NT plants, disrupted the dynamic equilibrium of the antioxidant system, and compromised cellular stability. The severity of freezing damage increased with decreasing temperature and prolonged exposure. Chlorophyll (a/b) ratio (Chl (a/b)), maximum quantum yield of photosystem II (Fv/Fm), soluble sugar, and malondialdehyde (MDA) were identified as key indicators for assessing physiological and biochemical changes in NT plants. Utilizing these four parameters, a comprehensive score (CS) model of freezing damage was developed to quantitatively evaluate the growth status of NT plants across varying low-temperature freezing damage gradients and durations. Subsequently, the freezing damage grade index for NT plants during the overwintering period was established. Specifically, Level 1 for CS ≤ −0.50, Level 2 for −0.5 < CS ≤ 0, Level 3 for 0 < CS ≤ 0.5, and Level 4 for 0.5 < CS. The research results provide valuable data for agricultural meteorological departments to carry out disaster monitoring, early warning, and prevention and control.

Effect of BTHWA Biostimulation on Lettuce Using Chlorophyll Fluorescence, Gas Exchange, and Thermography

The aim of this study was to examine lettuce using different concentrations of the biostimulator N-methyl-N-methoxyamide-7-carboxybenzo(1.2.3)thiadiazole (BTHWA), a new benzothiadiazole derivative. Different concentrations of BTHWA during watering and spraying were applied to lettuce. Chlorophyll fluorescence, gas exchange, thermal images, and plant parameter data were used to study physiological process and the growth of lettuce. Chlorophyll fluorescence data showed a strong effect after the first BTHWA application to lettuce. After three applications, the plants were harvested and data were recorded. Similarly, in the second experiment, gas exchange and thermal images were recorded after the first treatment of BTHWA. Our findings showed improved chlorophyll efficiency after the first BTHWA application, and no adverse effects were recorded on the overall photochemistry at any concentration. Regarding growth parameters, spraying BTHWA reduced the fresh weight but decreased the damage index. A lower watering concentration (0.066 mg/L) applied three times did not cause any damage to plants and fresh weight, even after repeated applications. Infrared thermal images showed BTHWA application also significantly affected plant temperature. Gas exchange data revealed that sprayed plants exhibited higher transpiration rates, stomatal conductance, and photosynthetic rates when compared to watered and control plants. This study suggests that application of a low dose of BTHWA is safe to use in agriculture practices in lettuce without compromising its growth and yield.

In thermotolerance tests of tropical tree leaves, the chlorophyll fluorescence parameter Fv/Fm measured soon after heat exposure is not a reliable predictor of tissue necrosis.

Tropical rainforests are hot and may be particularly sensitive to ongoing anthropogenic global warming. This has led to increased interest in the thermotolerance of tropical trees. Thermotolerance of leaves of two tropical tree species, Terminalia catappa and Coccoloba uvifera, was determined by exposing leaf samples to 15-min heat treatments, followed by measurements of potential photosystem II quantum yield (dark-adapted value of variable/maximum chlorophyll a fluorescence, Fv/Fm) after 24 h and 14 days, and visible damage (necrosis) after 14 days. T50 (24 h), the temperature at which Fv/Fm declined by 50% 24 h after heat treatments, was associated with only ~10% leaf area damage in C. uvifera and no damage in T. catappa. In neither species was leaf necrosis observed at T5 (24 h), the temperature at which Fv/Fm declined by 5%. In both species, temperatures significantly higher than T50 (24 h) were required for 50% leaf area necrosis to occur. T50 (14 days) was a better proxy of visible leaf damage than T50 (24 h). The relationship between heat-induced Fv/Fm decline and tissue necrosis varies among species. In species surveys of leaf thermal tolerances, calibration of the Fv/Fm assay against the necrosis test is recommended for each species under investigation. Fv/Fm measurements soon after heat exposure do not reliably predict irreversible heat damage and may thus not be suitable to model and predict the thermostability of tropical forest trees.

Effects of Abscisic Acid on the Physiological and Biochemical Responses of Saccharina japonica Under High-Temperature Stress

Saccharina japonica is one of the most productive aquatic plants in the world, widely used in food, feed, medicine, and other industries. Predominantly inhabiting temperate marine environments in mid- to high-latitude regions of the Northern Hemisphere, the growth of S. japonica is significantly limited by high-temperature stress. Abscisic acid (ABA) plays an important role in plant growth and development and stress responses. However, the role of ABA on high-temperature stress tolerance in S. japonica still needs to be further elucidated. Here, we found that exogenous ABA significantly alleviated disease and decay in S. japonica under high-temperature stress while also increasing the relative growth rate, chlorophyll fluorescence parameters, photosynthetic pigment, and osmotic substance content. Meanwhile, exogenous ABA enhanced the activity of protective enzymes and up-regulated the transcript levels of antioxidant-related genes, thereby reducing oxidative damage. Most importantly, we observed a significant increase in ABA content and the transcript levels of key genes involved in ABA synthesis in S. japonica under high-temperature stress, which were further amplified by the addition of exogenous ABA. In conclusion, this study provides evidence that ABA can moderate the detrimental effects of high-temperature stress and provides a theoretical basis for the screening of S. japonica germplasm resources and the cultivation of new stress-resistant varieties.

Relationships Between Photosynthetic Efficiency and Grain Antioxidant Content of Barley Genotypes Under Increasing Nitrogen Rates

Nitrogen fertilization may affect the functioning of photosynthesis as well as the chemical composition and antioxidant potential of cereal grains. Little is known about the relationship between the efficiency of photosynthesis and the content of phenolic compounds in barley grain, especially in conditions of varying nitrogen availability. In this regard, a field experiment was conducted to examine the responses of two primary barley genotypes with elevated phenolic compound content (TPC) in grain and an intensive modern cultivar H. v. vulgare with high protein content to increasing nitrogen fertilization (rates of 0, 30, 60 and 90 kg N ha−1) during the study years, which differed in terms of hydrothermal conditions. The leaf greenness index (SPAD) and chlorophyll fluorescence parameters were evaluated on three occasions throughout the growing season. Following the harvest, the chemical composition of the grains, including phenolic acids, flavonoids and antioxidant potential, was evaluated. The antioxidant potential and chemical composition of the grain, including TPC and protein content, depended to the greatest extent on genetic and environmental factors, and only then on nitrogen fertilization. Nitrogen increased the TPC content and antioxidant capacity ABTS+ of the grains of all studied genotypes and the protein content in H. v. vulgare grain. Rates of 60 and 90 kg N ha−1 resulted in a significant increase in the SPAD, PIabs and Fv/Fm in BBCH 34 and 57. A positive correlation was confirmed between the SPAD and PIabs and the content of TPC and ABTS+ in the grain. The dependence of qualitative characteristics on the Fv/Fm was also demonstrated. The primary genotypes are characterized by a greater genetic potential for the synthesis of phenolic compounds than the modern cultivar H. v. vulgare. The synthesis of phenolic compounds, and thus their accumulation in the grain, is clearly stimulated by unfavorable environmental factors and moderate nitrogen rates and depends on the chlorophyll content in the leaves and the efficiency of photosynthesis. N fertilization has a beneficial effect on the content of phenolic compounds in grain resulting from the improvement in the SPAD and PIabs. The chemical composition of grain and the increase in antioxidant potential are determined by the Fv/Fm, which is low under hydrothermal stress conditions.

Response of growth and chlorophyll fluorescence parameters of mulberry seedlings to waterlogging stress

This study aimed to investigate the adaptive mechanisms of mulberry (Morus alba) to waterlogged conditions, with a specific focus on the development of adventitious roots (ARs), alteration of growth strategies, and adjustment of chlorophyll fluorescence parameters. To achieve this goal, 4-year-old potted mulberry plants were selected for research, and a waterlogging simulation method was implemented. Four treatments were established to investigate the effects of varying water conditions on leaf waterlogging damage, the number of ARs, plant height, chlorophyll fluorescence parameters, and proton motive force (pmf) parameters in mulberry plants. These treatments included the control group (CK), shallow submerged group (SS), half-submerged group (HS) and deep submerged group (DS). Our results showed that (1) The number of ARs in each group increased with increasing waterlogging time. (2) Waterlogging stress inhibited the height growth of mulberry, and the changes in plant height in the HS and DS groups were significantly lower than those in the CK and SS groups. (3) The maximum photochemical quantum yield (Fv/Fm) in the HS and DS groups decreased significantly under waterlogging stress. The nonphotochemical quenching (NPQt) of mulberry leaves in the submergence group increased significantly in the early stage of waterlogging stress, and the NPQt in the submergence group increased continuously with increasing waterlogging time. (4) Thylakoid conductivity to protons (gH+) in the leaves of mulberry decreased significantly under waterlogging stress, whereas the steady-state rate of proton flux (vH+) and total electrochromic shift (ECSt) increased significantly. The morphological, physiological, and ecological responses of mulberry plants to waterlogging stress include the timely generation of ARs at the stem base, the adjustment of plant growth strategies, and the repair of photosynthetic response centers in leaves through heat dissipation and thylakoid acidification mechanisms.

Effect of Watering Gradient on Chlorophyll Fluorescence Parameters of Prunus domestica Trees

Mature 5-year-old Prunus domestica trees were used as research objects in plantation areas in arid and semi-arid regions of northern China in Hohhot city; three irrigation gradients and a natural control were set up according to the determination of wilting coefficient and field capacity, and FluorCam 1000-H chlorophyll fluorescence parameters of plant leaves were determined by using a portable chlorophyll fluorescence imager. The results showed that the effects of irrigation gradients on potential photochemical efficiency, maximum photochemical efficiency and non-photochemical burst were not significant (p > 0.05), and the effects on photochemical burst were significant (p < 0.05) at different fertility periods. The potential photochemical efficiency, maximum photochemical efficiency and photochemical burst basically showed a trend of increasing and then decreasing, and the non-photochemical burst showed a trend of decreasing and then increasing during different fertility periods. During the same fertility period, the potential and maximum photochemical efficiencies were significantly increased, and the photochemical and non-photochemical bursts were somewhat reduced under the full irrigation gradient. Therefore, the chlorophyll fluorescence characteristics of Prunus domestica trees at different fertility stages can be regulated by controlling the irrigation gradient to increase the activity of photosystem II (PSII), which in turn improves the photosynthesis of the plants.

Physiological and metabolomic analyses reveal the mechanism by which exogenous spermine improves drought resistance in alfalfa leaves (Medicago sativa L.).

Alfalfa (Medicago sativa L.) is a globally important legume crop with high nutritional and ecological value. Drought poses a serious threat to alfalfa acreage and yields. Spermine (Spm) has been shown to protect plants from drought damage. The aim of this study was to clarify the mechanism of exogenous Spm to improve drought resistance of alfalfa. In this study, we root applied 0.1, 0.5, and 1 mM Spm to Gannong No. 3 (G3) alfalfa under drought stress, and then determined their physiological and metabolic changes. The results showed that exogenous Spm increased chlorophyll content, chlorophyll fluorescence parameters and gas exchange parameters, enhanced antioxidant enzymes activity, improved ascorbic acid-glutathione (AsA-GSH) cycle, increased osmoregulatory substances content, reduced hydrogen peroxide and superoxide anion levels, and inhibited malondialdehyde accumulation in alfalfa under drought stress, thereby increasing plant height and leaf relative water content and enhancing drought tolerance of alfalfa. The redundancy analysis of the above physiological indicators showed that the addition of the optimal Spm to improve drought tolerance of alfalfa under drought stress was mainly achieved by increasing catalase activity and improving the ASA-GSH cycle. In addition, metabolomics analysis revealed that exogenous Spm increased the content of oxobutanedioic acid, citric acid, fumaric acid and malic acid to enhance the tricarboxylic acid cycle. Meanwhile, exogenous Spm increased endogenous Spm and proline (Pro) content to resist drought stress by enhancing Spm and Pro metabolism. Moreover, exogenous Spm increased the accumulation of the signaling substance abscisic acid. In conclusion, exogenous Spm enhanced drought resistance of alfalfa leaves under drought stress.

Acute toxicity of salicylic acid and its derivatives on the diatom Phaeodactylum tricornutum: Physico-Biochemical and transcriptomic insights

Salicylate pollutants (SAs) poses a serious threat to marine ecosystems as emerging contaminants. However, the toxic effects of SAs on marine phytoplankton, as well as the potential mechanisms and their ecological risks linked with them, are remain largely unknown. In this study, we aimed to evaluate the toxic effects of salicylic acid (SA) and its 5-substituted derivatives (5-sSA) on the marine diatom Phaeodactylum tricornutum, as well as the potential molecular mechanism involved in the toxicity. Physiological assays conducted on P. tricornutum revealed significant changes in photosynthetic pigments, chlorophyll fluorescence parameters, and antioxidant enzyme activities. The results showed that exposure of P. tricornutum to SAs caused a significant decline in chlorophyll contents and damage to the photosystem II (PSII) core resulting in the decline of photosynthesis. Although the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were enhanced, oxidative damage occurred. Transcriptome analysis showed that a large number of differentially expresses genes (DEGs) were significantly enriched in metabolic pathways such as porphyrin metabolism, terpenoid backbone biosynthesis, and carbon fixation in photosynthetic organisms after SA and 5-BrSA treatments. In addition, key genes in transcriptomic metabolic pathways were further analyzed and validated using weighted correlation network analysis (WGCNA) and real-time fluorescence quantitative PCR (qPCR). Considering the above results, SAs mainly inhibit the processes of photosynthesis by repressing the expression of genes involved in secondary metabolite synthesis and photosynthetic carbon sequestration pathways, thus exerting toxic effects on algal cells. The results of the study will provide key data for understanding the ecological risk and toxicity mechanisms of SA pollutants.

Chlorophyll Fluorescence in Wheat Breeding for Heat and Drought Tolerance

The constantly growing need to increase the production of agricultural products in changing climatic conditions makes it necessary to accelerate the development of new cultivars that meet the modern demands of agronomists. Currently, the breeding process includes the stages of genotyping and phenotyping to optimize the selection of promising genotypes. One of the most popular phenotypic methods is the pulse-amplitude modulated (PAM) fluorometry, due to its non-invasiveness and high information content. In this review, we focused on the opportunities of using chlorophyll fluorescence (ChlF) parameters recorded using PAM fluorometry to assess the state of plants in drought and heat stress conditions and predict the economically significant traits of wheat, as one of the most important agricultural crops, and also analyzed the relationship between the ChlF parameters and genetic markers.

Evaluating crop nitrogen status in maize leaves: A predictive modelling approach using chlorophyll fluorescence parameters

The consumption of chemical fertilizers has increased eight-fold since the 19th century, outstripping crop yields increases and, emphasizing the need for precise nitrogen (N) assessment in crops to optimize fertilization and mitigate environmental impacts. This study developed a model using chlorophyll fluorescence technology to accurately evaluate the N status in maize leaves while addressing the limitations of current labor-intensive and environmentally sensitive methods. Based on a long-term experiment initiated in 2011, maize hybrid Fumin 985 was sampled in 2021 and 2022 under two crop-straw management strategies (SM: no tillage with surface straw mulch, SP: plough tillage with straw incorporation) and six N application rates. Partial least squares regression (PLSR) models were formulated using chlorophyll fluorescence parameters (ChlF) to assess leaf N content (N leaf). The results indicated that a N application rate of 270 kg ha−1 sufficed to meet crop N requirements. Leaf characteristics such as N leaf, total pigment content (TP), and leaf dry weight (DW leaf) changed significantly with increasing N application rates, influencing rapid chlorophyll fluorescence (OJIP) dynamics. Principal component analysis (PCA) reduced ChlF from 35 to 21, and four models were developed, among which, the model using ChlF and TP was more accurate than the model using DW alone. Key ChlF parameters for PLSR model performance included ABS/RC, φ(Eo), ETo/CSm, and δ(Ro)/(1–δ(Ro)). Although non-destructive N leaf detection using chlorophyll fluorescence technology proved feasible, additional leaf characteristics, such as TP, are necessary to improve model accuracy. Considering local field conditions is essential for the application of this technology at a larger scale. Precise evaluation of N status using chlorophyll fluorescence is beneficial for a more efficient N management and sustainable agriculture.

Tolerance and phytoremediation capacity of atrazine and S-metolachlor by two duckweeds.

The phytotoxicity and removal of atrazine and S-metolachlor in sterile duckweed systems were estimated in this study. Herbicides were added at environmentally relevant ranges: 0-400µg/L for atrazine or 0-200µg/L for S-metolachlor in systems with Spirodela polyrhiza or Lemna minor. Toxicity biomarkers, i.e., changes in plant biomass, surface area, chlorophyll fluorescence parameters, pigments, lipid peroxidation, protein concentration, and antioxidative enzyme activities in plants were estimated after 7days. S. polyrhiza (RGRbiomass-EC50 = 164.8µg/L) was more tolerant to atrazine than L. minor (RGRbiomass-EC50 = 101.0µg/L). Atrazine caused damage to photosystem II (ΦM), a reduction in electron transport between PSII and PSI (Φ'M), as well as disruption in energy distribution pathways (decrease in qPrel and increase in UQFrel), most prominently in L. minor. However, L. minor (RGRbiomass-EC50 = 128.9µg/L) was more tolerant to S-metolachlor than S. polyrhiza (RGRbiomass-EC50 = 15.5μg/L). The highest sensitivity of S. polyrhiza to S-metolachlor was attributed to a decrease in absorbed energy used in photochemistry (qPrel) and an increase in lipid peroxidation, indicating that S. polyrhiza plants were experiencing oxidative stress. Residual pesticide analysis in the water after seven days allowed us to conclude that plants were responsible for reducing up to 16.5% of atrazine and 28.7% of S-metolachlor in the duckweed system. S. polyrhiza showed higher atrazine phytoremediation capacity than L. minor. S. polyrhiza was more efficient at an environmentally relevant concentration of S-metolachlor (25μg/L) and L. minor at higher concentrations (200μg/L).

Combining clinostating and proton irradiation for modeling the space environment: a case study with a Chernobyl accession of Arabidopsis thaliana

Purpose The study of mechanisms of plant responses to extreme conditions, particularly, microgravity and ionizing radiation, is crucial for space exploration. Modern space biology of plants focuses on increasing plant tolerance to harsh conditions of space environment. Given the limited access to the International Space Station, we designed and assembled the 3D clinostat for mimicking microgravity, which, in combination with proton irradiation, allows simulating space conditions. As a case study for testing the device, we studied the effect of clinostating on Arabidopsis thaliana accession originating from the Chernobyl exclusion zone. Materials and Methods Using the combined clinostating and proton irradiation, we simulated the conditions of long-term space flight for Arabidopsis thaliana plants of the Chernobyl accession – progeny of chronically irradiated plants, grown from field-collected (Masa-0) and laboratory-cultivated (Masa-0-1) seeds, and for wild-type Col-8. The clinostating and irradiation of plants were also carried out separately. Plant responses were studied as photosynthetic and phenotypic endpoints of seedlings. Results and Conclusions Parameters of chlorophyll fluorescence estimated immediately after exposure showed that Masa-0-1 plants were resistant to the simulated space conditions, while Masa-0 demonstrated modulation of non-photochemical fluorescence quenching. Proton irradiation generally inhibited photosynthesis of Masa-0, Masa-0-1, and Col-8 seedlings. The combined effect of irradiation and clinostating modulated the photosynthetic activity of Col-8 seedlings. The leaf area of seedlings did not change after exposure to simulated conditions. The 3D clinostat model and software are published along with this article for researchers interested in the field of space biology.

PGPR alleviated the negative effects of low temperature and low light stress on the growth and physiology of violet plants

Plants in greenhouses are often exposed to low temperature and low light conditions in the winter, and this has a major effect on flower cultivation. Inoculation of plant growth-promoting rhizobacteria (PGPR) can improve the growth of plants under stress. Here, we examined the effects of Pseudomonas fluorescens on the growth, photosynthesis, chlorophyll fluorescence parameters, and antioxidant enzyme systems of violet plants (Matthiola incana) exposed to normal temperature and normal light intensity (18 °C/11 °C, 500 μmol·m-2·s-1, NN), low temperature and normal light intensity (4 °C/1 °C, 500 μmol·m-2·s-1, LN), normal temperature and low light intensity (18 °C/11°C, 100 μmol·m-2·s-1, NL), and low temperature and low light intensity (4 °C/1 °C, 100 μmol·m-2·s-1, LL). The results showed that the plant height, stem diameter, leaf area, shoot fresh/dry weight, and underground fresh/dry weight of violet inoculated with PGPR were 40%, 17%, 13%, 25%, 41%, 30%, and 38% higher than the control, respectively. In addition, the total root length, mean root diameter, number of root tips, number of bifurcated root tips, and root vigor were 24%, 23%, 14%, 30%, and 21% higher in the inoculated group than in the control group, respectively. PGPR promoted chlorophyll accumulation in plants, and the net photosynthetic rate of violets was 32% higher in plants inoculated with PGPR than in control plants. PGPR also significantly promoted the maximum photochemical conversion efficiency of photosystem II (PSII) and the potential activity of PSII under UV light. After inoculation with PGPR, the content of MDA decreased by 16.8%, and the activities of superoxide dismutase and peroxidase increased by 19.2% and 20.0%, respectively. Therefore, PGPR can promote the growth of violet plants by increasing the photosynthetic capacity, activating the antioxidant enzyme system, and reducing damage induced by exposure to low light intensity.

Impact of Pulse Electric Field Stimulation on Negative Air Ion Release Capacity of Snake Plants

To investigate the effects of pulse electric field stimulation on the photosynthetic electron transport chain and negative air ion (NAI) release capacity of snake plants, the chlorophyll content, fluorescence induction kinetics curve (OJIP curve), chlorophyll fluorescence parameters, and NAI release concentration of snake plants kept under identical greenhouse conditions under different pulse electric field stimulations were compared and analyzed. The experimental results show that (1) after pulse electric field stimulation, the chlorophyll content in treatment group T1 (5 kv) and T2 (7 kv) of snake plants increased by 6.30% and 6.70%, respectively, with significant differences observed between the two treatment groups and the control group (CK). (2) In both treatment groups, the OJIP curve exhibited higher values for the inflection point (I) and peak (P) compared to the origin (O) and inflection point (J) values, with the rising trend in the I–P segment being more gentle than that of the O–J segment. Additionally, the J band was above 0, with the peak value in the T2 group being higher than that in the T1 group. (3) The chlorophyll fluorescence parameters showed fluctuating variations. Specifically, Fm, TRo/CSo, ETo/CSo, and DIo/CSo showed ascending trends in the treatment groups. Fv/Fo, Sm, and ABS/RC exhibited descending trends; Fv/Fm, Vj, ETo/RC, and φEo showed relatively minor changes. The PIabs displayed a decreasing trend. The PItotal in the CK was greater than that in the T1 and T2 groups. (4) After 4 h of pulse electric field stimulation, the NAI concentration increased by 87.60% in the T1 group and by 62.09% in the T2 group, compared to the same measurement taken at 3 h. Pulse electric field impacts the photosynthetic electron transport chain of snake plants, thereby influencing their NAI release capacity. This study aims to elucidate the physiological responses of the chloroplasts in snake plants to pulsed electric field stimulation and to lay the foundation for enhancing the plant’s release of negative air ion concentrations through physical and technological means.

Variation in Leaf Functional Traits of Populus laurifolia Ldb and Ulmus pumila L. Across Five Contrasting Urban Sites in Ulaanbaatar, Mongolia.

Amid urbanization, studying leaf functional traits of woody plants in urban environments is essential for understanding how urban green spaces function and how they can be effectively managed sustainably. In this study, we investigated the effects of different growing conditions on the morpho-physiological traits of Populus laurifolia and Ulmus pumila across five contrasting urban sites. The leaf area (LA), leaf length (LL), leaf width (LW), leaf biomass (LB), specific leaf area (SLA), leaf chlorophyll concentration, chlorophyll fluorescence parameters, leaf water potential at predawn (Ψpd) and midday (Ψmd), leaf performance index (PIabs), and phenotypic plasticity index (PPI) were compared across five contrasting urban sites. The soil chemical and physical properties were also compared between sites. There were significant differences in soil physicochemical characteristics between sites. We found significant effects of site on most of the morpho-physiological traits measured, except for Ψmd. The leaf chlorophyll concentration of P. laurifolia and U. pumila varied significantly between sites. The Ψpd was significantly different between years and sites. In U. pumila, the mean PPI for morphological traits (0.20) was lower than that for physiological traits (0.21). In conclusion, we revealed significant variations in the morpho-physiological traits of P. laurifolia and U. pumila across the five urban sites. Hence, long-term, large-scale studies are recommended to examine how diverse species respond to different urban growing conditions and to include other ecologically important plant traits for a better understanding of urban trees in a changing environment.

Phosphorus mitigates the adverse effects of microplastics pollution on wheat and maize: Impacts on growth, photosynthesis, and antioxidant defense

Microplastics (MP) pollution in agricultural soils has become an important environmental problem. Phosphorus (P) is a key nutrient for plant growth. P fertilizers are mainly applied to agricultural fields to achieve the high production expected by farmers. The experiment included two MP levels (0, 1 % w/w) and two P levels (0 mg kg−1, 200 mg kg−1) in order to know whether MP effects on wheat and maize are regulated by supplemental P supply. MP decreased plant height, photosynthetic pigment, and chlorophyll fluorescence parameters, while increased ROS and MDA contents. Wheat and maize exhibited distinct strategies in mitigating growth damage caused by MP pollution: wheat primarily increased the AsA contents, while maize predominantly enhanced APX activity. P supply alleviated the MP pollution effect by improving photosynthetic pigments, POD, and PPO activity in wheat and maize. P supply alleviated the MP pollution effect by improving antioxidant enzyme activities in the AsA-GSH cycling in wheat, while increasing non-enzymatic antioxidant contents in the AsA-GSH cycling in maize. The results showed that wheat and maize resisted MP pollution by different mechanisms, and P supply reduced the sensitivity of wheat and maize to MP pollution and its regulatory effect on wheat was better than that on maize. SynopsisThe response of different plants under the same microplastic and phosphorus conditions is limited. We find phosphorus alleviates microplastics pollution on wheat and maize through different regulatory routes.

Photoprotective mechanisms activated in Antarctic moss <i>Chorisodontium aciphyllum</i> during desiccation

We investigated the relationship between relative water content (RWC) of Antarctic moss Chorisodontium aciphyllum and several chlorophyll fluorescence parameters evaluating primary photochemical processes of photosynthesis. During the gradual dehydration of Ch. aciphyllum from fully wet (RWC=100%) to dry (RWC=0%) state, progression of NPQ (non-photochemical quenching) induction curves were recorded; the maximum NPQ (NPQmax) attained at the end of illumination period (10 min.), and NPQ relaxation in dark were all analysed. Induction curves of photosynthetic electron transport rate (ETR) were also evaluated, as well as two parameters, ETRmax and initial slop, were derived from the curve: (1) ETRmax; (2) initial slope (a parameter). The two parameters were related to the degree of desiccation (RWC decdlining from 100 to 0%). It was found that NPQ induction curves and the parameters derived from them were sensitive to dehydration and may be used as markers for dehydration-induced changes in photosystem II functioning of desiccating Ch. aciphyllum. The activation of non-photochemical quenching during desiccatin and the underlying mechanisms are discussed.

Photoinhibition and recovery of primary photosynthesis in Antarctic and subantarctic lichens. Analysis of interspecific differences

This study meticulously investigates the dynamics of photoinhibition and the mechanisms of primary photosynthetic activity recovery in lichens found in Antarctica and the sub-Antarctic regions. Advanced methodologies were utilised, such as Kautsky's kinetic analysis and the OJIP test. The study carefully details the response of various lichen species to intense light stress, outlining both immediate effects and subsequent recovery processes. Our findings reveal that these lichens employ a range of adaptive strategies, specific to each species, to mitigate the effects of photoinhibition, thereby emphasizing their remarkable resilience and ecological importance in harsh environments. Notably, the investigation reveals the sophisticated interplay between inherent photoprotective mechanisms and the ecological adaptations that enable these lichens to thrive under such harsh conditions. The study not only advances our knowledge of plant physiology under stress but also enriches our insights into the survival strategies of terrestrial organisms facing global environmental changes. Three types of photoinhibitory treatments differing in their duration and strength were applied to 7 lichen species from Antarctica and South America (Isla Navarino). The lichens responded with a decrease in photosynthetic processes in photosystem II (FV/FM and ΦPSII declined), although they showed almost complete recovery in the following 5 h. This was attributed to the activation of photoprotective mechanisms, non-photochemical quenching (NPQ) in particular, during photoinhibitory treatments. Chlorophyll fluorescence parameters derived from slow Kautsky kinetics were correlated with those derived from the OJIP curve. Our study presents data that supports the conclusion of significant photoresistance of the studied lichen species in the hydrated state to photoinhibition induced by high doses of photosynthetically active radiation (PAR).

Inversion Modeling of Chlorophyll Fluorescence Parameters in Cotton Canopy via Moisture Data and Spectral Analysis

The study of chlorophyll fluorescence parameters is very important for understanding plant photosynthesis. Monitoring cotton chlorophyll fluorescence parameters via spectral technology can aid in understanding the photosynthesis, growth, and stress of cotton fields in real time and provide support for cotton growth regulation and planting management. In this study, cotton plot experiments with different water treatments were set up to obtain the spectral reflectance of the cotton canopy, the maximum photochemical quantum yield (Fv/Fm), and the photochemical quenching coefficient (qP) of leaves at different growth stages. Support vector machine regression (SVR), random forest regression (RFR), and artificial neural network regression (ANNR) were used to establish a fluorescence parameter inversion model of the cotton canopy leaves. The results show that the original spectrum was transformed by multivariate scattering correction (MSC), the standard normal variable (SNV), and continuous wavelet transform (CWT), and the model constructed with Fv/Fm passed accuracy verification. The SNV-SVR model at the budding stage, the MSC-SVR model at the early flowering stage, the SNV-SVR model at the full flowering stage, the MSC-SVR model at the flowering stage, and the CWT-SVR model at the full boll stage had the highest estimation accuracy. The accuracies of the three spectral preprocessing and qP models were verified, and the MSC-SVR model at the budding stage, SNV-SVR model at the early flowering stage, MSC-SVR model at the full flowering stage, SNV-SVR model at the flowering stage, and CWT-SVR model at the full boll stage presented the highest estimation accuracies.