Photosynthetic Performance Research Articles

Eco-physiological trait variation in widely occurring species of Western Himalaya along elevational gradients reveals their high adaptive potential in stressful conditions.

Species distributed across a wide elevation range have broad environmental tolerance and adopt specific adaptation strategies to cope with varying climatic conditions. The aim of this study is to understand the patterns of variation in leaf eco-physiological traits that are related to the adaptation of species with a wide distribution in different climatic conditions. We studied the variability in eco-physiological traits of two co-occurring species of Western Himalaya (Rumex nepalensis and Taraxacum officinale), along elevational gradients. We conducted our study in elevations ranging from 1000 to 4000m a.s.l. in three transects separated in an eco-region spanning 2.5° latitudes and 2.3° longitudes in the Western Himalaya. We hypothesized substantial variation in eco-physiological traits, especially increased net rate of photosynthesis (PN), Rubisco specific activity (RSA), and biochemicals at higher elevations, enabling species to adapt to varying environmental conditions. Therefore, the photosynthetic measurements along with leaf sampling were carried out during the months of June-August and the variations in photosynthetic performance and other leaf traits were assessed. Data was analyzed using a linear mixed effect model with 'species,' 'elevation' as fixed and 'transect' as random factor. Elevation had a significant effect on majority of traits. It was found that PN and maximum carboxylation rate of Rubisco (Vcmax) have unimodal or declining trend along increasing elevations. High RSA was observed at higher elevations in all the three transects. Trends for biochemical traits such as total soluble sugars, total soluble proteins, proline, and total phenolics content suggested an increase in these traits for the survival of plants in harsh environments of higher elevations. Our study reveals that although there is considerable variation in the eco-physiological traits of the two species across elevational gradients of different transects, there are certain similarities in the patterns that depict their high adaptive potential in varying climatic conditions.

Purification of Chloroplast Envelope, Thylakoids, and Stroma from Angiosperm Leaves.

Plant cell chloroplasts are bounded by a two-membrane envelope. Their photosynthetic function is based on the development of an operational large internal membrane network, called the thylakoids, and on enzymatic processes present in the chloroplast matrix, called the stroma. Thylakoid membranes are distinct from the chloroplast envelope, and their biogenesis is dependent on biosynthetic and transport activities specific of the chloroplast envelope. Starting with the isolation of intact chloroplasts, the method presents the separation by differential centrifugation of the three compartments. A protocol is detailed for leaves of spinach, Arabidopsis or pea.

Relative effects of melatonin and hydrogen sulfide treatments in mitigating salt damage in wheat.

Soil salinity poses a significant threat to agricultural productivity, impacting the growth and yield of wheat (Triticum aestivum L.) plants. This study investigates the potential of melatonin (MT; 100 µM) and hydrogen sulfide (H2S; 200 µM sodium hydrosulfide, NaHS) to confer the tolerance of wheat plants to 100 mM NaCl. Salinity stress induced the outburst of reactive oxygen species (ROS) resulting in damage to the chloroplast structure, growth, photosynthesis, and yield. Application of either MT or NaHS augmented the activity of antioxidant enzymes, superoxide dismutase, ascorbate peroxidase, glutathione reductase, and reduced glutathione (GSH) levels, upregulated the expression of Na+ transport genes (SOS1, SOS2, SOS3, NHX1), resulting in mitigation of salinity stress. Thus, improved stomatal behavior, gas-exchange parameters, and maintenance of chloroplast structure resulted in enhanced activity of the Calvin cycle enzymes and overall enhancement of growth, photosynthetic, and yield performance of plants under salinity stress. The use of DL-propargylglycine (PAG, an inhibitor of hydrogen sulfide biosynthesis) and p-chlorophenyl alanine (p-CPA, an inhibitor of melatonin biosynthesis) to plants under salt stress showed the comparative necessity of MT and H2S in mitigation of salinity stress. In the presence of PAG, more pronounced detrimental effects were observed than in the presence of p-CPA, emphasizing that MT was involved in mitigating salinity through various potential pathways, one of which was through H2S.

Evaluating non-photochemical quenching (NPQ) kinetics and photosynthetic efficiency in cassava (Manihot esculenta) subjected to variable high light conditions.

Light intensity is a critical environmental factor influencing plant growth and development. To survive high light conditions, plants have evolved various protective mechanisms, including non-photochemical quenching (NPQ). However, NPQ can limit effective photosynthetic yield when transitioning to low light conditions. This phenomenon is underexplored in cassava (Manihot esculenta ), a starchy storage root crop known for its high biological efficiency and climate resilience. To address this knowledge gap, we assessed the photoprotective abilities and growth responses of six cassava varieties under natural environmental light conditions (control) and intermittent high light (IHL) conditions by adding 900μmolm-2 s-1 using full-spectrum LED lights, on top of the natural ambient daylight. Our results demonstrated a significant impact of light treatment on aboveground biomass, total crop biomass, chlorophyll a and b content, photosynthetic rate, and NPQ values during transitions from low to high light and vice versa. Notably, cassava variety 'Sree Suvarna' exhibited the highest yield under both control and IHL conditions. These findings suggest that screening cassava varieties for their ability to postpone photoinhibition and recover quickly from photoinhibition may enhance photosynthetic performance. Such strategies have important implications for improving the efficiency and resilience of cassava crops, ultimately contributing to sustainable agricultural productivity.

Enhancing Spinach growth and yield through the synergistic effects of Rhizobacter-Enriched compost

Plant Growth-Promoting Rhizobacteria (PGPR) and compost present promising solutions for bolstering agricultural sustainability by stimulating plant growth and yield while lessening dependence on chemical inputs. Our investigation delved into the combined effects of PGPR and compost on spinach cultivation, conducted at Amity University’s Organic Farm. Employing a Randomized Block Design (RBD) with six treatments and three replications, we evaluated how these treatments influenced spinach growth parameters and photosynthetic pigment levels. Results showed that treatment T5 (AIOA Strain + Compost) outperformed others, significantly boosting plant height, leaf breadth, root length, and leaf count per plant. Furthermore, T5 exhibited elevated chlorophyll and carotenoid levels, indicating enhanced photosynthetic function and overall plant vigor. These outcomes underscore the potential synergy between PGPR and compost in fostering sustainable crop production. By diminishing reliance on chemical fertilizers and pesticides while enhancing soil health and nutrient cycling, integrating PGPR and compost-based biofertilizers offers an economical and environmentally friendly avenue for augmenting agricultural productivity and mitigating environmental hazards. Further exploration into optimization techniques and underlying mechanisms is crucial to fully harness the potential of these microbial and organic interventions across varied agroecological settings. Overall, this study contributes to advancing our knowledge of employing microbial and organic methods in sustainable agriculture, crucial for addressing global challenges in food security and environmental conservation.

Effect of Metal Nanoparticles on Photosynthetic and Antioxidant Enzyme Activities of Soybean

This study presents the effects of nanoscale zerovalent cobalt (NZVC) on the photosynthetic activity and expression of genes related to the photosynthetic apparatus as well as the activity of antioxidant enzymes in soybean (Glycine max L. Merr). Treatment of soybean seeds with NZVC solution (at concentrations of 0.17; 0.33 and 100 mg/kg seed) has increased the efficiency of light energy absorbed by photosystem II, improved photosynthetic efficiency, and maintained the function of photosynthetic apparatus when plant growth is reduced by enhancing the value of photosynthetic parameters (Fo, Fm, Fv/Fm, ETR, FPSII) compared with the control. The expression of genes involved in photosynthesis in soybean leaves was changed by growth time and NZVC treatment concentration. The psaA, Lhca, psbA, and psbB genes had increased expression levels at 17 and 32 days after sowing, then decreased at 70 days after sowing. The expression of the psbE, and Cyt b6f genes was greater than the control during the growth period. Treatment of soybean seeds with high concentrations of NZVC (0.33 and 100 mg/kg seed) did not negatively affect the photosynthetic function of soybean plants. The activity of nitrate and nitrite reductases and antioxidant enzymes including superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase of cobalt-treated plants were better than those of the control. This is a defense mechanism of plants to minimize the harmful effects of these stresses. This result has elucidated the mechanism of increasing the yield of soybean when its seeds were treated with NZVC.

The impact of drying on the structure and photosynthesis of boreal peatland vegetation

Boreal peatlands harbour large stores of carbon as peat below their surfaces. Climate change is expected to cause drying in northern peatlands, which will in turn impact the carbon balance of these ecosystems that is maintained by high water tables and the hydrologically sensitive plants growing there. This study aims to quantify how vegetation will be structured (I) and photosynthesize (II, III) in a future climate as emulated by long-term water level drawdown (WLD). To do this, changes in the vegetation and its photosynthesis after WLD are linked, and the response of Sphagnum mosses to periodic drought is investigated. Field measurements were done at a long-term WLD field experiment that contained a rich (mesotrophic) fen, a poor (oligotrophic) fen and a bog (ombrotrophic) site. Measurements included vegetation surveys from existing permanent sample plots and leaf-level carbon dioxide exchange measurements. For an experiment in controlled conditions peatland surface cores from this field experiment were transported to a greenhouse where the photosynthesis of lawn Sphagna during and after an experimental periodic drought was measured. The field study revealed that the response of peatland vegetation to WLD depend on peatland type. The species composition in the rich fen was the most impacted by WLD, while the bog vegetation demonstrated stability. Similarly, large increases in photosynthesis occurred following WLD on the vascular plant-covered rich fen, while changes were negligible on the Sphagnum-carpeted bog. The vegetation on the two fens shifted from an open sedge-, or sedge and Sphagnum-dominated ecosystem, to a tree-dominated ecosystem. Canopy development following WLD further accelerated vegetation changes by shading and sheltering the understorey vegetation. Vascular plants were the most likely to increase productivity from WLD as they are best suited to utilize the nutrients made available by peat mineralization, while Sphagnum moss photosynthesis was impacted little. The greenhouse study revealed that lawn Sphagnum mosses exposed to long-term WLD were more vulnerable to drought compared to those from wet sites. Large capitula typical to fen Sphagnum species appeared to be beneficial for surviving periodic drought. This work demonstrated that climate change as emulated by long-term WLD will have a large impact on the vegetation composition of northern peatlands and increase photosynthetic function of these ecosystems, fens in particular. To better predict climate feedbacks from these changes, carbon dynamics including peatland vegetation dynamics should be updated in global process models. Future research to better understand the tipping point of different peatland types after WLD in different climatic regions will help us to predict changes in these diverse and globally important systems.

Impact of Sodium Nitroprusside on the Photosynthetic Performance of Maize and Sorghum.

Nitric oxide (NO) is an important molecule in regulating plant growth, development and photosynthetic performance. This study investigates the impact of varying concentrations (0-300 µM) of sodium nitroprusside (SNP, a donor of NO) on the functions of the photosynthetic apparatus in sorghum (Sorghum bicolor L. Albanus) and maize (Zea mays L. Kerala) under physiological conditions. Analysis of the chlorophyll fluorescence signals (using PAM and the JIP-test) revealed an increased amount of open PSII reaction centers (qP increased), but it did not affect the number of active reaction centers per PSII antenna chlorophyll (RC/ABS). In addition, the smaller SNP concentrations (up to 150 μM) alleviated the interaction of QA with plastoquine in maize, while at 300 μM it predominates the electron recombination on QAQB-, with the oxidized S2 (or S3) states of oxygen evolving in complex ways in both studied plant species. At the same time, SNP application stimulated the electron flux-reducing end electron acceptors at the PSI acceptor side per reaction center (REo/RC increased up to 26%) and the probability of their reduction (φRo increased up to 20%). An increase in MDA (by about 30%) and H2O2 contents was registered only at the highest SNP concentration (300 µM). At this concentration, SNP differentially affected the amount of P700+ in studied plant species, i.e., it increased (by 10%) in maize but decreased (by 16%) in sorghum. The effects of SNP on the functions of the photosynthetic apparatus were accompanied by an increase in carotenoid content in both studied plants. Additionally, data revealed that SNP-induced changes in the photosynthetic apparatus differed between maize and sorghum, suggesting species specificity for SNP's impact on plants.

Phenotypic plasticity for improved light harvesting, in tandem with methylome repatterning in reef-building corals.

Acclimatization through phenotypic plasticity represents a more rapid response to environmental change than adaptation and is vital to optimize organisms' performance in different conditions. Generally, animals are less phenotypically plastic than plants, but reef-building corals exhibit plant-like properties. They are light dependent with a sessile and modular construction that facilitates rapid morphological changes within their lifetime. We induced phenotypic changes by altering light exposure in a reciprocal transplant experiment and found that coral plasticity is a colony trait emerging from comprehensive morphological and physiological changes within the colony. Plasticity in skeletal features optimized coral light harvesting and utilization and paralleled significant methylome and transcriptome modifications. Network-associated responses resulted in the identification of hub genes and clusters associated to the change in phenotype: inter-partner recognition and phagocytosis, soft tissue growth and biomineralization. Furthermore, we identified hub genes putatively involved in animal photoreception-phototransduction. These findings fundamentally advance our understanding of how reef-building corals repattern the methylome and adjust a phenotype, revealing an important role of light sensing by the coral animal to optimize photosynthetic performance of the symbionts.

Enhanced Stomatal Conductance Supports Photosynthesis in Wheat to Improved NH4+ Tolerance.

The impact of ammonium (NH4+) stress on plant growth varies across species and cultivars, necessitating an in-depth exploration of the underlying response mechanisms. This study delves into elucidating the photosynthetic responses and differences in tolerance to NH4+ stress by investigating the effects on two wheat (Triticum aestivum L.) cultivars, Xumai25 (NH4+-less sensitive) and Yangmai20 (NH4+-sensitive). The cultivars were grown under hydroponic conditions with either sole ammonium nitrogen (NH4+, AN) or nitrate nitrogen (NO3-, NN) as the nitrogen source. NH4+ stress exerted a profound inhibitory effect on seedling growth and photosynthesis in wheat. However, these effects were less pronounced in Xumai25 than in Yangmai20. Dynamic photosynthetic analysis revealed that the suppression in photosynthesis was primarily attributed to stomatal limitation associated with a decrease in leaf water status and osmotic potential. Compared to Yangmai20, Xumai25 exhibited a significantly higher leaf K+ concentration and TaAKT1 upregulation, leading to a stronger stomatal opening and, consequently, a better photosynthetic performance under NH4+ stress. In conclusion, our study suggested stomatal limitation as the primary factor restricting photosynthesis under NH4+ stress. Furthermore, we demonstrated that improved regulation of osmotic substances contributed to higher stomatal conductance and enhanced photosynthetic performance in Xumai25.

Growth and photosynthetic physiology of holopelagic Sargassum (Phaeophyceae) under laboratory conditions

SummarySpecies of holopelagic Sargassum are responsible for Caribbean golden tides, commonly known as ‘Sargassum events’. These events mainly comprise Sargassum fluitans and Sargassum natans I, which are exposed to high levels of irradiance, but also self‐shading within their floating masses. In this study, we grew S. fluitans and S. natans I and acclimated them to low‐light conditions at 23°C in the laboratory to explore their responses to increasing light intensities. Photosynthesis, respiration, growth, and pigment content were evaluated over 3 weeks. S. fluitans and S. natans I photoacclimate to higher irradiances by decreasing their chlorophyll a and c contents. An increase in maximum photosynthesis and respiration rates was observed under high light, although differences occurred in the saturation irradiance and the initial slope of the photosynthesis versus irradiance curve. These adjustments were reflected in S. fluitans daily growth (from 2% to 7% d−1 at low to high light, respectively) and tissue nitrogen content (1.6–2.7%) but were absent in S. natans I (~1% d−1). The photosynthetic physiology of S. fluitans under these conditions suggests lower light requirements without compromising growth; however, under high light a higher photosynthetic performance was observed. Combining physiological and growth studies in holopelagic Sargassum species will serve as a baseline to understand and explain the success and overgrowth of these species along the Caribbean coast.

Ecophysiological characterisation of a Klebsormidium strain isolated from a cave environment

Members of the genus Klebsormidium are ubiquitously distributed over the Earth and are among the major biological soil crust (BSC) forming microalgae. Their representatives can be found in terrestrial, aquatic, polar, desert regions and have been investigated so far from various aspects. However, the available information about Klebsormidium isolates from lamp-flora is very limited. In our work, we examined a Klebsormidium strain isolated from a Hungarian cave. The temperature optimum of its photosynthetic performance was tested by oxygen yield measurements and pulse-amplitude-modulated fluorescence, which were completed by determination of specific growth rates at different temperatures, from 10 to 40 °C. In addition, we also evaluated the brassinosteroid (BR) content of these cultures. Our results indicated that the studied microalga is capable of growing from 10 to 40 °C, with a 20–25 °C temperature optimum; these findings were in accordance with the observed hormone levels. Regarding photosynthetic performance, the oxygen yield and chlorophyll fluorescence measurements showed maxima at 30–40 °C and 35–40 °C, respectively. Moreover, the examined Klebsormidium strain demonstrates traits associated with cave adaptation, i.e., by high light utilisation factor (α) and diminished light adaptation parameter (Ik) values.

Synergistic effects of salt and ultraviolet radiation on the rice-field cyanobacterium Nostochopsis lobatus HKAR-21.

Environmental variation has a significant impact on how organisms, including cyanobacteria, respond physiologically and biochemically. Salinity and ultraviolet radiation (UVR)-induced variations in the photopigments of the rice-field cyanobacterium Nostochopsis lobatus HKAR-21 and its photosynthetic performance was studied. We observed that excessive energy dissipation after UVR is mostly caused by Non-Photochemical Quenching (NPQ), whereas photochemical quenching is important for preventing photoinhibition. These findings suggest that ROS production may play an important role in the UVR-induced injury. To reduce ROS-induced oxidative stress, Nostochopsis lobatus HKAR-21 induces the effective antioxidant systems, which includes different antioxidant compounds like carotenoids and enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). The study indicates that Nostochopsis lobatus HKAR-21 exposed to photosynthetically active radiation + UV-A + UV-B (PAB) and PAB + NaCl (PABN) had significantly reduced photosynthetic efficiency. Furthermore, maximum ROS was detected in PAB exposed cyanobacterial cells. The induction of lipid peroxidation (LPO) has been investigated to evaluate the impactof UVR on the cyanobacterial membrane in addition to enzymatic defensive systems. The maximal LPO level was found in PABN treated cells. Based on the findings of this research, it was concluded that salinity and UVR had collegial effects on the major macromolecular components of the rice-field cyanobacterium Nostochopsis lobatus HKAR-21.

Exogenous application of melatonin protects bean and tobacco plants against ozone damage by improving antioxidant enzyme activities, enhancing photosynthetic performance, and preventing membrane damage

Ozone (O3) pollution is harmful to plants and ecosystems. Several chemicals have been evaluated to protect plants against O3 deleterious effects. However, they are not adequately efficient and/or the environmental safety of their application is questioned. Hence, new chemicals that provide sufficient protection while being safer for environmental application are needed. This study investigates the response of two O3-sensitive plant species (Phaseolus vulgaris L. cv. Pinto and Nicotiana tabacum L. cv. Bel-W3) leaf-sprayed with deionized water (W, control), ethylenediurea (EDU, 1 mM) or melatonin at lower (1 mM) or higher (3 mM) concentrations (Mel_L and Mel_H, respectively), and then exposed to a square wave of 200 ppb O3, lasting 1 day (5 h day−1) for bean and 2 days (8 h day−1) for tobacco. In both species, the photosynthetic activity of O3-exposed plants was about halved. O3-induced membrane damage was also confirmed by increased malondialdehyde (MDA) byproducts compared to control (W). In EDU- and Mel-treated bean plants, the photosynthetic performance was not influenced by O3, leading to reduction of the incidence and severity of O3 visible injury. In bean plants, Mel_L mitigated the detrimental effect of O3 by boosting antioxidant enzyme activities or osmoprotectants (e.g. abscisic acid, proline, and glutathione transferase). In Mel_L-sprayed tobacco plants, O3 negatively influenced the photosynthetic activity. Conversely, Mel_H ameliorated the O3-induced oxidative stress by preserving the photosynthetic performance, preventing membrane damage, and reducing the visible injuries extent. Although EDU performed better, melatonin protected plants against O3 phytotoxicity, suggesting its potential application as a bio-safer and eco-friendlier phytoprotectant against O3. It is worth noting that the content of melatonin in EDU-treated plants remained unchanged, indicating that the protectant mode of action of EDU is not Mel-related.

Root-zone aeration improves fruit yield and quality of tomato by enhancement of leaf photosynthetic performance

Heavy irrigation and soil compaction cause hypoxic stress in plant roots, which limits crop growth. This issue can be solved by root-zone aeration, but the photophysiological responses of crop plants to the dissolved oxygen (DO) concentration in irrigation water remain unclear. Here, a greenhouse plot experiment was conducted to investigate the changes in leaf photosynthesis and plant growth of tomato (Solanum lycopersicum L. cv. ‘Omanda 3′) under aerated irrigation with various DO concentrations. Plants were treated with three different levels of aeration: 5 mg L–1 DO (conventional subsurface irrigation as a non-aeration control), 15 mg L–1 DO (low aeration treatment), and 30 mg L–1 DO (high aeration treatment). Compared with the control, the aeration treatments promoted electron transport from the primary to secondary plastoquinone acceptors (QA to QB) of photosystem II (PSII) and increased leaf net photosynthetic rate in plants at the seedling, fruit expansion, and maturation stages. The opposite effects of aeration treatments were observed at the flowering and fruit-setting stage. The enhancement of leaf photosynthetic performance contributed to improved plant growth, fruit yield, and quality of tomato as a result of increased oxygen supply in the root zone. The aeration treatments additionally facilitated the biosynthesis and transport of photosynthetic carbon assimilates in plant tissues, as evidenced by increased starch and sucrose contents in the leaves and sucrose content in the roots. However, under the high aeration level, excessive transport of sucrose from leaves to roots hindered further improvements in tomato yield and biomass at the maturation stage. Based on plant photophysiological and yield performance, aerated irrigation with a low concentration of DO (15 mg L–1) is recommended for greenhouse tomato crops during the seedling, fruit expansion, and maturation stages, and there is no need of root-zone aeration at the flowering and fruit-setting stage.

Effects of Sodium Selenite on the Growth and Photosystem II Activity of Arthrospira platensis Gom.

Arthrospira platensis (A. platensis) is a species of cyanobacteria with high economic value; the species is commercially well known as Spirulina platensis, and A. platensis was used in this paper. Its high adaptability, high photosynthetic efficiency, and fast growth rate make it one of the few cyanobacteria that can be cultivated on a large scale. Therefore, using the selenium enrichment property of A. platensis to cultivate selenium-enriched A. platensis will not only enhance the physiological efficacy of A. platensis but also increase its economic value significantly. In this study, we investigated the effects of sodium selenite on the growth and photosynthetic performance of A. platensis selenium by setting different amounts and methods of sodium selenite addition, and we explored the optimal culture conditions of the best dosage and method of sodium selenite addition. The results showed that the experimental group treated with sodium selenite at 700 μmol/L had the fastest growth, and the contents of soluble protein, phycocyanin C, and chlorophyll a increased by approximately 67.9%, 1.44 times, and 38.8% compared to the control group, respectively. Superoxide dismutase (SOD) and catalase (CAT) activity increased by 1.88-fold and 65%, respectively, and malondialdehyde (MDA) levels were reduced by 62% compared to the control group. The results of the OJIP assay showed that the J and I points were significantly higher at the batch addition and treatment concentration of 700 μmol/L, with the rate of QA being reduced and the proportion of the slowly reduced PQ pool being increased. The values of the maximum light energy conversion efficiency (Fv/Fm) per unit of reaction center were higher in both sodium selenite treatment groups than in the control group, indicating that the light energy conversion efficiency of A. platensis was promoted under all concentration treatment conditions. The batch addition of sodium selenite at concentrations less than 700 μmol/L resulted in significantly higher ABS/RC values than the control, and they were far superior to the one-time addition method. The reason for this may have been that the batch addition of sodium selenite at low concentrations increased the light absorption capacity of the unit reaction center of PSII, resulting in a rise in captured light energy, a rise in the energy captured by the reaction center for electron transfer (ETo/RC), a decrease in the energy dissipated in the absorption of light energy by the reaction center (DIo/RC), and an increase in the photosynthetic performance index (PI abs).

The Effects of Shading on the Photosynthetic Performance of Endangered Plant Horsfieldia hainanensis Seedlings

Shading is one of the management practices for preventing the damage or injury of plant seedlings during extreme weather and climate events, such as very high temperatures and heat stress. In this study, we investigated the effects of different shading conditions on the photosynthetic characteristics of the endangered plant Horsfieldia hainanensis in Guangxi, China. The H. hainanensis seedlings in this study underwent five shading treatments, including 20% (L1), 40% (L2), 60% (L3), 80% (L4), and 100% (control) of full sunlight. The net growth of their diameter and height, and photosynthetic gas exchange parameters including their photosynthesis rate (Pn), transpiration rate (Tr), intercellular CO2 concentration (Ci), and water use efficiency (WUE) were measured for the examined seedlings. The OJIP curve and 820 nm light absorption curve, and the osmotic substances and products of membrane lipid peroxidation were employed to assess photosynthetic capacity, identify the factors constraining photosynthetic carbon assimilation, and investigate the mechanisms influencing photosystem II (PSII) and photosystem I (PSI) in the seedlings under shade stress. The results showed that the seedlings in the L2 treatments had the highest net growth and Pn, the best photosynthetic performance, and the best coordination between PSII and PSI. The net photosynthesis (Pn) levels exhibited a declining trend in the following order: L2 > L3 > L4 > L1. In the L1 treatment, non-stomatal factors emerged as the primary determinant affecting the Pn of the seedlings. The performance index (potential) of PSII, representing the conservation of absorbed photon energy to intersystem electron acceptor reduction (PIABS and ΔI/I0) of the seedlings, decreased in the order of L2 > L3 > L4 > L1. The photosystem performance and the coordination between PSII and PSI (Φ(PSI/PSII)) of the seedlings decreased in the order of L2 > L1 > L3 > L4. Under the low and moderate shading stresses (L1–L3), more serious damages occurred in PSII than in PSI, including on the donor side of PSII and in the electron transfer from QB to the acceptor side of PSI. In contrast, more considerable injury occurred in PSI than in PSII under the stress of the heavy shading treatment (L4). Considering the alterations in their leaf osmotic regulatory substances and membrane lipid peroxidation products, our findings indicate that the L2 treatment was the most conducive to the growth of the H. hainanensis seedlings. In contrast, the L1 treatment subjected H. hainanensis seedlings to the most significant stress, resulting in substantial damage to their growth and photosynthetic mechanisms. Our research provides a scientific insight into and a practical guide for the selection of an appropriate light intensity for the conservation and cultivation of endangered plant species, such as H. hainanensis.

Cascading effects from soil to maize functional traits explain maize response to microplastics disturbance in multi-nutrient soil environment

Microplastics (MPs) is a major threat to agroecosystems. Their accumulation and impacts should be evaluated to advance our understanding of soil function and health. Uncovering the role of cascade effects in regulating crop growth is crucial to understanding the link between MPs disturbance and environmental functions. Therefore, we aimed to assess how the cascade changes between (non-) biological factors and functional traits of maize regulate the response of maize growth to MPs in different nutrient soil environments. We found that soil dehydration induced by MPs may disrupt the balance of the physiological status of maize, negatively affect photosynthetic performance, and enhance competition among organisms for limited nutrients. However, root-responsive nutrient cues with a high degree of tectonic freedom allowed adaptive phenotypic plasticity to occur, masking the negative effects of MPs. In nutrient-rich soil environments, moderate and high intensity (>0.5 %) MPs disturbances initiated root nutrient foraging activities, and maize tended to decrease its cost of investing in root construction, i.e., increasing specific root length (SRL) to promote its own growth. The growth of maize was mainly characterized by increases in the belowground biomass (BGB, 7.11 to 20.81 g) and aboveground biomass (AGB, 61.11 to 118.26 g). Our study suggests that a cascade effect between environmental factors initiated by MPs and the functional architecture of the maize root system drives maize to regulate its growth by responding to nutrient cues. These findings will help to ensure food security, formulate environmental risk management policies and protect soil health, especially in the context of future agriculture.

Foliar zinc spraying improves assimilative capacity of sugar beet leaves by promoting magnesium and calcium uptake and enhancing photochemical performance

Sugar beet, a zinc-loving crop, is increasingly limited by zinc deficiency worldwide. Foliar zinc application is an effective and convenient way to supplement zinc fertilizer. However, the regulatory mechanism of foliar zinc spraying on sugar beet leaf photosynthetic characteristics remains unclear. Therefore, we investigated the effects of foliar ZnSO4·7H2O application (0, 0.1%, 0.2%, and 0.4%) on the photosynthetic performance of sugar beet leaves under controlled hydroponic conditions. The results indicated that a foliar spray of 0.2% Zn fertilizer was optimal for promoting sugar beet leaf growth. This concentration significantly reduced the leaf shape index of sugar beet, notably increasing leaf area, leaf mass ratio, and specific leaf weight. Foliar spraying of Zn (0.2%) substantially elevated the Zn content in sugar beet leaves, along with calcium (Ca) and magnesium (Mg) contents. Consequently, this led to an increase in the potential photochemical activity of PSII (Fv/Fo) (by 6.74%), net photosynthetic rate (Pn) (11.39%), apparent electron transport rate (ETR) (11.43%), actual photochemical efficiency of PSⅡ (Y (Ⅱ)) (11.46%), photochemical quenching coefficient (qP) (15.49%), and total chlorophyll content (25.17%). Ultimately, this increased sugar beet leaf dry matter weight (11.30%). In the cultivation and management of sugar beet, the application of 0.2% Zn fertilizer (2.88 mg plant−1) exhibited the potential to enhance Zn and Mg contents in sugar beet, improve photochemical properties, stimulate leaf growth, and boost light assimilation capacity. Our result suggested the foliar application of Zn might be a useful strategy for sugar beet crop management.

Synthetic polyploid induction influences morphological, physiological, and photosynthetic characteristics in Melissa officinalis L.

Melissa officinalis L., a well-known herb with diverse industrial and ethnopharmacological properties. Although, there has been a significant lack in the breeding attempts of this invaluable herb. This study aimed to enhance the agronomical traits of M. officinalis through in vitro polyploidization. Nodal segments were micropropagated and subjected to oryzalin treatment at concentrations of 20, 40, and 60 mM for 24 and 48 hours. Flow cytometry, chromosome counting, and stomatal characteristics were employed to confirm the ploidy level of the surviving plants. The survival rate of the treated explants decreased exponentially with increasing oryzalin concentration and duration. The highest polyploid induction rate (8%) was achieved with 40 mM oryzalin treatment for 24 hours. The induced tetraploid plants exhibited vigorous growth, characterized by longer shoots, larger leaves, and a higher leaf count. Chlorophyll content and fluorescence parameters elucidated disparities in photosynthetic performance between diploid and tetraploid genotypes. Tetraploid plants demonstrated a 75% increase in average essential oil yield, attributed to the significantly larger size of peltate trichomes. Analysis of essential oil composition in diploid and tetraploid plants indicated the presence of three major components: geranial, neral, and citronellal. While citronellal remained consistent, geranial and neral increased by 11.06% and 9.49%, respectively, in the tetraploid population. This effective methodology, utilizing oryzalin as an anti-mitotic agent for polyploid induction in M. officinalis, resulted in a polyploid genotype with superior morpho-physiological traits. The polyploid lemon balm generated through this method has the potential to meet commercial demands and contribute significantly to the improvement of lemon balm cultivation.