Terrestrial ecosystems, increased solar ultraviolet radiation, and interactions with other climate change factors

Effects of temperature up-shift and UV-A radiation on fatty acids content and expression of desaturase genes in cyanobacteria Microcystis aeruginosa: stress tolerance and acclimation responses

Temperature up-shift and UV-A radiation effects on growth, lipid damage, fatty acid (FA) composition and expression of desaturase genes desA and desB were investigated in the cyanobacteria Microcystis aeruginosa. Although UV-A damaging effect has been well documented, reports on the interactive effects of UV radiation exposure and warming on cyanobacteria are scarce. Temperature and UV-A doses were selected based on the physiological responses previously obtained by studies with the same M. aeruginosa strain used in this study. Cells pre-grown at 26 °C were incubated at the same temperature or 29 °C and exposed to UV-A + PAR and only PAR for 9 days. Growth rate was significantly affected by UV-A radiation independently of the temperature throughout the experiment. High temperature produced lipid damage significantly higher throughout the experiment, decreasing at day 9 as compared to 26 °C. In addition, the cells grown at 29 °C under UV-A displayed a decrease in polyunsaturated FA (PUFA) levels, with ω3 PUFA being mostly affected at the end of exposure. Previously, we reported that UV-A-induced lipid damage affects differentially ω3 and ω6 PUFAs. We report that UV-A radiation leads to an upregulation of desA, possibly due to lipid damage. In addition, the temperature up-shift upregulates desA and desB regardless of the radiation. The lack of lipid damage for UV-A on ω3 could explain the lack of transcription induction of desB. The significant ω6 decrease at 26 °C in cells exposed to UV-A could be due to the lack of upregulation of desA.

Potential of UV-B radiation in drought stress resilience: A multidimensional approach to plant adaptation and future implications

The escalating impact of climate change and ultraviolet (UV) radiation is subjecting plants to unique combinations of UV-B and drought stress. These combined stressors could have additive, synergistic, or antagonistic effects, but the precise nature of these impacts remains uncertain, hampering our ability to predict plant adaptations approach towards stressors. Our analysis of various studies shows that UV-B or drought conditions detrimentally influence plant growth and health metrics by the enhanced generation of reactive oxygen species causing damage to lipids, proteins, carbohydrates and DNA. Further reducing biomass accumulation, plant height, photosynthetic efficiency, leaf area, and water transpiration, while enhancing stress-related symptoms. In response to UV-B radiation and drought stress, plants exhibit a notable up-regulation of specific acclimation-associated metabolites, including proline, flavonoids, anthocyanins, unsaturated fatty acids, and antioxidants. These metabolites play a pivotal role in conferring protection against environmental stresses. Their biosynthesis and functional roles are potentially modulated by signalling molecules such as hydrogen peroxide, abscisic acid, jasmonic acid, salicylic acid, and ethylene, all of which have associated genetic markers that further elucidate their involvement in stress response pathways. In comparison to single stress, the combination of UV-B and drought induces the plant defence responses and growth retardation which are less-than-additive. This sub-additive response, consistent across different study environments, suggests the possibility of a cross-resistance mechanism. Our outlines imply that the adverse effects of increased drought and UV-B could potentially be mitigated by cross-talk between UV-B and drought regimes utilizing a multidimensional approach. This crucial insight could contribute significantly to refining our understanding of stress tolerance in the face of ongoing global climate change.

Differential Antioxidant Response to Supplemental UV-B Irradiation and Sunlight in Three Basil Varieties

Three basil plant varieties (Ocimum basilicum var. Genovese, Ocimum × citriodorum, and Ocimum basilicum var. purpurascens) were grown under moderate light (about 300 µmol photons m-2 s-1) in a glasshouse or growth chamber and then either transferred to an open field (average daily dose: 29.2 kJ m-2 d-1) or additionally exposed to UV-B irradiation in a growth chamber (29.16 kJ m-2 d-1), to reveal the variety-specific and light-specific acclimation responses. Total antioxidant capacity (TAC), phenolic profile, ascorbate content, and class III peroxidase (POD) activity were used to determine the antioxidant status of leaves under all four light regimes. Exposure to high solar irradiation at the open field resulted in an increase in TAC, total hydroxycinnamic acids (HCAs, especially caffeic acid), flavonoids, and epidermal UV-absorbing substances in all three varieties, as well as a two-fold increase in the leaf dry/fresh weight ratio. The supplemental UV-B irradiation induced preferential accumulation of HCAs (rosmarinic acid) over flavonoids, increased TAC and POD activity, but decreased the ascorbate content in the leaves, and inhibited the accumulation of epidermal flavonoids in all basil varieties. Furthermore, characteristic leaf curling and UV-B-induced inhibition of plant growth were observed in all basil varieties, while a pro-oxidant effect of UV-B was indicated with H2O2 accumulation in the leaves and spotty leaf browning. The extent of these morphological changes, and oxidative damage depended on the basil cultivar, implies a genotype-specific tolerance mechanism to high doses of UV-B irradiation.

Susceptibility of Diaphorina citri to Irradiation with UV-A and UV-B and the Applicability of the Bunsen-Roscoe Reciprocity Law

Populations of Diaphorina citri decline with elevation and, in a study in Bhutan, were rarely found above 1200 m ASL. The impact of ultraviolet (UV) radiation, particularly UV-B, on immature stages of the psyllid was proposed as limiting factor. As no studies have been undertaken on the influences of UV radiation on the development of D. citri, we examined the effects of UV-A and UV-B on different stadia of the psyllid. In addition, compliance with the Bunsen-Roscoe reciprocity law was examined. Irradiation with UV-A marginally reduced egg hatch and the survival times of emerging nymphs. Early instar nymphs were little affected by this waveband, but the survival of adults was reduced at the higher doses used. With UV-B, egg hatch and the survival times of early and late instar nymphs declined in proportion to UV-B dose. A dose of 57.6 kJ m^-2 d^-1 reduced the survival time of only adult females. Female fecundity was reduced at high UV-A and UV-B doses but increased at low doses. The Bunsen-Roscoe law held true for eggs and early instar nymphs for different durations and irradiances of UV-B. Eggs and nymphs had ED₅₀ values for UV-B lower than the daily fluxes of this wavelength experienced worldwide. Thus, UV-B could be a factor causing the psyllid to be scarce at high elevations.

Ultraviolet-B radiation in relation to agriculture in the context of climate change: a review

Over the past few decades, the amount of ultraviolet-B radiation (UV-B) reaching the earth's surface has been altered due to climate change and stratospheric ozone dynamics. This narrow but highly biologically active spectrum of light (280-320 nm) can affect plant growth and development. Depletion of ozone and climate change are interlinked in a very complicated manner, i.e., significantly contributing to each other. The interaction of climate change, ozone depletion, and changes in UV-B radiation negatively affects the growth, development, and yield of plants. Furthermore, this interaction will become more complex in the coming years. The ozone layer reduction is paving a path for UV-B radiation to impact the surface of the earth and interfere with the plant's normal life by negatively affecting the plant's morphology and physiology. The nature and degree of the future response of the agricultural ecosystem to the decreasing or increasing UV-B radiation in the background of climate change and ozone dynamics are still unclear. In this regard, this review aims to elucidate the effects of enhanced UV-B radiation reaching the earth's surface due to the depletion of the ozone layer on plants' physiology and the performance of major cereals.

Responses of flavonoids to solar UV radiation and gradual soil drying in two Medicago truncatula accessions

Ground level UV-B (290-315 nm) and UV-A (315-400 nm) radiation regulates multiple aspects of plant growth and development. In a natural environment, UV radiation interacts in a complex manner with other environmental factors (e.g., drought) to regulate plants' morphology, physiology, and growth. To assess the interactive effects of UV radiation and soil drying on plants' secondary metabolites and transcript abundance, we performed a field experiment using two different accessions of Medicago truncatula (F83005-5 French origin and Jemalong A17 Australian origin). Plants were grown for 37 days under long-pass filters to assess the effects of UV short wavelength (290-350 nm, UV_sw) and UV-A long wavelength (350-400 nm, UV-A_lw). Soil-water deficit was induced by not watering half of the plants during the last seven days of the experiment. The two accessions differed in the concentration of flavonoids in the leaf epidermis and in the whole leaf: F83005-5 had higher concentration than Jemalong A17. They also differed in the composition of the flavonoids: a greater number of apigenin derivatives than tricin derivatives in Jemalong A17 and the opposite in F83005-5. Furthermore, UV_sw and soil drying interacted positively to regulate the biosynthesis of flavonoids in Jemalong A17 through an increase in transcript abundance of CHALCONE SYNTHASE (CHS). However, in F83005-5, this enhanced CHS transcript abundance was not detected. Taken together the observed metabolite and gene transcript responses suggest differences in mechanisms for acclimation and stress tolerance between the accessions.

The Role of Reactive Oxygen Species in Plant Response to Radiation

Radiation is widespread in nature, including ultraviolet radiation from the sun, cosmic radiation and radiation emitted by natural radionuclides. Over the years, the increasing industrialization of human beings has brought about more radiation, such as enhanced UV-B radiation due to ground ozone decay, and the emission and contamination of nuclear waste due to the increasing nuclear power plants and radioactive material industry. With additional radiation reaching plants, both negative effects including damage to cell membranes, reduction of photosynthetic rate and premature aging and benefits such as growth promotion and stress resistance enhancement have been observed. ROS (Reactive oxygen species) are reactive oxidants in plant cells, including hydrogen peroxide (H₂O₂), superoxide anions (O₂^•-) and hydroxide anion radicals (·OH), which may stimulate the antioxidant system of plants and act as signaling molecules to regulate downstream reactions. A number of studies have observed the change of ROS in plant cells under radiation, and new technology such as RNA-seq has molecularly revealed the regulation of radiative biological effects by ROS. This review summarized recent progress on the role of ROS in plant response to radiations including UV, ion beam and plasma, and may help to reveal the mechanisms of plant responses to radiation.

Divergent response and adaptation of specific leaf area to environmental change at different spatio-temporal scales jointly improve plant survival

Specific leaf area (SLA) is one of the most important plant functional traits. It integrates multiple functions and reflects strategies of plants to obtain resources. How plants employ different strategies (e.g., through SLA) to respond to dynamic environmental conditions remains poorly understood. This study aimed to explore the spatial variation in SLA and its divergent adaptation through the lens of biogeographic patterns, evolutionary history, and short-term responses. SLA data for 5424 plant species from 76 natural communities in China were systematically measured and integrated with meta-analysis of field experiments (i.e., global warming, drought, and nitrogen addition). The mean value of SLA across all species was 21.8 m²  kg^-1 , ranging from 0.9 to 110.2 m²  kg^-1 . SLA differed among different ecosystems, temperature zones, vegetation types, and functional groups. Phylogeny had a weak effect on SLA, but plant species evolved toward higher SLA. Furthermore, SLA responded nonlinearly to environmental change. Unexpectedly, radiation was one of the main factors determining the spatial variation in SLA on a large scale. Conversely, short-term manipulative experiments showed that SLA increased with increased resource availability and tended to stabilize with treatment duration. However, different species exhibited varying response patterns. Overall, variation in long-term adaptation of SLA to environmental gradients and its short-term response to resource pulses jointly improve plant adaptability to a changing environment. Overall SLA-environment relationships should be emphasized as a multidimensional strategy for elucidating environmental change in future research.

Short-term recovery of soil and pine tree canopy after late prescribed burning in a semi-arid landscape

Climate change worsening due to global warming and progressive abandonment in rural areas mean that wildfires are increasing in extent and severity terms, and are one of the major disturbances in the Mediterranean Basin. To mitigate these disturbances, preventive management tools need to be used. Fire employment is being implemented, known as prescribed burnings, as forestry actions to change vegetation lines both vertically and horizontally to eliminate forest fuel load continuity. This study aimed to know the ecological effects of late prescribed burning treatments under mixed trees. Prescribed burns were carried out in October 2019 in the municipality of Ayna, Albacete (SE Spain). To assess the short-term (12-month) fire impact on soil, we measured soil respiration with a CO₂ flow chamber and analyzed soil physico-chemical properties. We also used minidisc infiltrometers to analyze soil repellency and soil hydraulic conductivity over a 1-year monitoring period. In addition, we evaluated the effects on tree strata by performing chemical nature analyses of fallen needles in Pinus pinaster after prescribed burning. According to our initial hypotheses, the results did not show significant changes in any parameter evaluated during the study period. However, some variables were affected in the first 3 months, needlefall and in microbiological activity, such as variations in soil physico-chemical properties, which can be due to long dry seasons combined with prescribed burning. This study attempts to observe and make known the effects that low-intensity prescribed burning has on soil and needlefall, which are relevant for updating forest management tools.

Effects of changes in UV-B radiation levels on biofilm-forming organisms commonly found in cultural heritage surfaces

Accurate measuring and monitoring methods available since the 1980s have shown that the amount of Ultraviolet B (UV-B) radiation reaching the Earth's surface has increased as a result of degradation of the ozone layer. Since the adoption of the Montreal Protocol in 1987, ozone levels have been recovering successfully. However, in the context of the current climate change, other factors such as changes in cloud patterns and an increased incidence of natural disasters (e.g. fires) may be disrupting this recovery. The present study aimed to investigate the effects of different UV-B radiation levels on biofilms colonising heritage monuments. For this purpose, the effects of current UV-B levels on a biofilm composed of Synechocystis sp. (a cyanobacterium), Bracteacoccus minor (a green alga) and Fusarium sp. (a fungus) were compared at three points along a South-North transect: Portugal, Galicia (NW Spain) and Ireland (from highest to lowest UV-B radiation, respectively). Increased levels of UV-B radiation caused changes in the growth, physiological state and composition of subaerial biofilms, with cyanobacteria being more resistant than green algae to high levels of UV-B. A reduction of fungal growth and extracellular polymer substances (EPS) production was also observed, related to the reduction of biofilm aggregation at high UV-B levels.

Involvement of Anthocyanin Biosynthesis of Cabernet Sauvignon Grape Skins in Response to Field Screening and In Vitro Culture Irradiating Infrared Radiation

To study the role of infrared (IR) radiation in the color change of the grape berry, field screening (IR-) and in vitro culture irradiation (IR+) were used. Acylated anthocyanin biosyntheses, including the biosynthesis of malvidin 3-O-glucoside, peonidin 3-O-glucoside, and their derivatives (acetylation and p-coumaroylation), were inhibited by IR-. IR+ promoted the biosynthesis of malvidin 3-O-glucoside and its derivatives, and IR+ inhibited the biosynthesis of peonidin 3-O-glucoside and its derivatives. WGCNA analysis revealed that the red module positively correlated with the flavonoid pathway. The hub genes were related to the anthocyanin pathway, including VvF3'5'H, VvANS, VvOMT1, VIT_18s0001g09400, and VvGST4. Further, the results revealed that transcription factors like RLK-Pelle, MYB, and C2H2 families were involved in response to IR radiation. Therefore, these results provide a complete understanding of IR radiation in grape skin color formation and the prospect of using supplemental light to improve the overall color of berries.

The differing responses of central carbon cycle metabolism in male and female Sargassum thunbergii to ultraviolet-B radiation

The enhancement of ultraviolet-B radiation (UV-B) radiation reaching the Earth's surface due to ozone layer depletion is an important topic. Macroalgal species growing in the intertidal zone are often directly exposed to UV-B radiation periodically as the tide changes. In order to better understand the response of macroalgae to UV-B stressed condition, we studied the dominant dioecious intertidal macroalgae Sargassum thunbergii. After consecutive UV-B radiation treatments, we used metabonomics models to analyze and compare the maximum photosynthetic electron transport rate (ETR_max), central carbon cycle metabolism (CCCM) gene expression level, CCCM enzymic activities [pyruvate dehydrogenase and citrate synthase (PDH and CS)], and carbon-based metabolite (including pyruvate, soluble sugar, total amino acid, and lipids) content in male and female S. thunbergii. The results showed that under low and high UV-B radiation, the ETR_max values and six targeted CCCM gene expression levels were significantly higher in males than in females. Under high UV-B radiation, only the CS activity was significantly higher in males than in females. There was no significant difference in PDH activity between males and females. The CCCM models constructed using the metabonomics analysis demonstrate that S. thunbergii males and females exhibit obvious gender differences in their responses to UV-B radiation, providing us with a new understanding of the macroalgal gender differences under UV-B radiation, as past investigations always underestimated their diecious characteristics.

Available Strategies for the Management of Andean Lupin Anthracnose

The lupin (Lupinus mutabilis Sweet) is a legume domesticated and cultivated for more than 4000 years by the pre-Hispanic cultures of the Andean zone. Due to its good taste and protein content, the lupin seed contributes significantly to the food and nutritional security of the Andean population. However, lupin is susceptible to diseases, and of these, anthracnose is the most devastating as it affects the whole crop, including leaves, stems, pods, and seeds. This review focuses on available strategies for management of lupin anthracnose from sowing to harvest. Seed disinfection is the primary anthracnose management strategy. Seed treatment with fungicides reduces transmission from seed to seedling, but it does not eradicate anthracnose. Attention is given to alternative strategies to limit this seed-borne pathogen as well as to enhance plant resistance and to promote plant growth. For anthracnose management in the field, integrated practices are discussed that encompass control of volunteer plants, lupin ontogenetic resistance, and rotation of biocontrol with chemical fungicides at susceptible phenological stages. This review covers some local experiences on various aspects of anthracnose management that could prove useful to other the groups focusing on the problem.

Climatic Drivers of the Complex Phenology of the Mediterranean Semi-Deciduous Shrub Phlomis fruticosa Based on Satellite-Derived EVI

A 21-year Enhanced Vegetation Index (EVI) time-series produced from MODIS satellite images was used to study the complex phenological cycle of the drought semi-deciduous shrub Phlomis fruticosa and additionally to identify and compare phenological events between two Mediterranean sites with different microclimates. In the more xeric Araxos site, spring leaf fall starts earlier, autumn revival occurs later, and the dry period is longer, compared with the more favorable Louros site. Accordingly, the control of climatic factors on phenological events was examined and found that the Araxos site is mostly influenced by rain related events while Louros site by both rain and temperature. Spring phenological events showed significant shifts at a rate of 1-4.9 days per year in Araxos, which were positively related to trends for decreasing spring precipitation and increasing summer temperature. Furthermore, the climatic control on the inter-annual EVI fluctuation was examined through multiple linear regression and machine learning approaches. For both sites, temperature during the previous 2-3 months and rain days of the previous 3 months were identified as the main drivers of the EVI profile. Our results emphasize the importance of focusing on a single species and small-spatial-scale information in connecting vegetation responses to the climate crisis.

Insights into the biosynthesis pathway of phenolic compounds in microalgae

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Microalgal PCs are important bioactive molecules beneficial for human health.

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Bioinformatic comparative exploration predicts PCs synthesis in microalgae.

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Ten groups of prokaryotic and eukaryotic microalgae reveal a conserved pathway core.

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Featured PCs can be restricted to diverse microalgae due to ecological implications.

Among the most relevant bioactive molecules family, phenolic compounds (PCs) are well known in higher plants, while their knowledge in microalgae is still scarce. Microalgae represent a novel and promising source of human health benefit compounds to be involved, for instance, in nutraceutical composition. This study aims to investigate the PCs biosynthetic pathway in the microalgal realm, exploring its potential variability over the microalgal biodiversity axis. A multistep in silico analysis was carried out using a selection of core enzymes from the pathway described in land plants. This study explores their presence in ten groups of prokaryotic and eukaryotic microalgae.. Analyses were carried out taking into account a wide selection of algal protein homologs, functional annotation of conserved domains and motifs, and maximum-likelihood tree construction. Results showed that a conserved core of the pathway for PCs biosynthesis is shared horizontally in all microalgae. Conversely, the ability to synthesize some subclasses of phenolics may be restricted to only some microalgal groups (i.e., Chlorophyta) depending on featured enzymes, such as the flavanone naringenin and other related chalcone isomerase dependent compounds.

Impact of polyploidy on plant tolerance to abiotic and biotic stresses

Polyploidy, defined as the coexistence of three or more complete sets of chromosomes in an organism's cells, is considered as a pivotal moving force in the evolutionary history of vascular plants and has played a major role in the domestication of several crops. In the last decades, improved cultivars of economically important species have been developed artificially by inducing autopolyploidy with chemical agents. Studies on diverse species have shown that the anatomical and physiological changes generated by either natural or artificial polyploidization can increase tolerance to abiotic and biotic stresses as well as disease resistance, which may positively impact on plant growth and net production. The aim of this work is to review the current literature regarding the link between plant ploidy level and tolerance to abiotic and biotic stressors, with an emphasis on the physiological and molecular mechanisms responsible for these effects, as well as their impact on the growth and development of both natural and artificially generated polyploids, during exposure to adverse environmental conditions. We focused on the analysis of those types of stressors in which more progress has been made in the knowledge of the putative morpho-physiological and/or molecular mechanisms involved, revealing both the factors in common, as well as those that need to be addressed in future research.

Static magnetic field treatment enhanced photosynthetic performance in soybean under supplemental ultraviolet-B radiation

The study was performed to analyze the impact of seed pretreatment by static magnetic field (SMF) of 200 mT for 1 h on photosynthetic performance of soybean (Glycine max) seedlings under ambient (aUV-B) and supplemental ultraviolet-B (a+sUV-B) stress. Ambient and supplemental UV-B were found to decrease the plant growth, chlorophyll concentration, PSII efficiency, selected JIP-test parameters such as Fv/Fm, φEo, ΔV(I-P), PIABS, PItotal, and rate of photosynthesis in the leaves of soybean seedlings emerged from untreated (UT) seeds. aUV-B and a+sUV-B were observed to increase the synthesis of UV-B-absorbing substances (UAS), reactive oxygen species (ROS) like superoxide radical (O2·-) and hydrogen peroxide (H2O2), antioxidants like ascorbic acid and α-tocopherol and decrease the nitrate reductase (NR) activity; subsequently, it results in a decreased rate of photosynthesis, biomass accumulation, and yield. However, our results provided evidence that SMF pretreatment increased the tolerance of soybean seedlings to UV-B radiation by increased NO content and NR activity; higher efficiency of PSII, higher values of φEo, ΔV(I-P), PIABS, and PItotal, decreased intercellular CO2 concentration, lower  amount of UAS, ROS, and antioxidants that consequently improve the yield of soybean plants under aUV-B as well as a+sUV-B stress. Thus, our results suggested that SMF pretreatment mitigates the adverse effects of UV-B stress by the enhancement in photosynthetic performance along with higher NO content which may be able to protect the plants from the deleterious effects of oxidative stress caused by UV-B irradiation.

Epigenetic and transcriptional responses underlying mangrove adaptation to UV-B

Tropical plants have adapted to strong solar ultraviolet (UV) radiation. Here we compare molecular responses of two tropical mangroves Avecennia marina and Rhizophora apiculata to high-dose UV-B. Whole-genome bisulfate sequencing indicates that high UV-B induced comparable hyper- or hypo-methylation in three sequence contexts (CG, CHG, and CHH, where H refers to A, T, or C) in A. marina but mainly CHG hypomethylation in R. apiculata. RNA and small RNA sequencing reveals UV-B induced relaxation of transposable element (TE) silencing together with up-regulation of TE-adjacent genes in R. apiculata but not in A. marina. Despite conserved upregulation of flavonoid biosynthesis and downregulation of photosynthesis genes caused by high UV-B, A. marina specifically upregulated ABC transporter and ubiquinone biosynthesis genes that are known to be protective against UV-B-induced damage. Our results point to divergent responses underlying plant UV-B adaptation at both the epigenetic and transcriptional level.

Bacterial-algae biofilm enhance MABR adapting a wider COD/N ratios wastewater: Performance and mechanism

Although membrane aerated biofilm reactor (MABR) is promising in nitrogen removal due to its counter-diffusion biofilms structure, it still cannot adapt a wider COD/N ratios wastewater. In this condition, expanding the MABR applicability range in different COD/N ratio wastewater is necessary. In this study, a bacterial-algae biofilm, instead of bacteria biofilm, supporting membrane aerated biofilm reactor (MABAR) was constructed, and the performance was compared to MABR. Results showed that the total nitrogen (TN) removal efficiency was promoted significantly in MABAR regardless of the COD/N ratio. Compared to MABR, effluent TN concentration in COD/N ratio of 2, 5, and 8 declined by 14.34 mg/L, 0.50 mg/L, and 12.10 mg/L, respectively. Nitrification inhibition test suggested that algae assimilation made an obvious contribution (at least 18.18 mg/L) to the NH₄⁺-N removal in MABAR. Besides, redundancy analysis (RDA) indicates that MABAR has a negative correlation with Nitrospirae but is positively correlated with NH₄⁺-N removal load. These results are consistent with the kinetics result that algae assimilation, instead of nitrification-denitrification, is responsible for the nitrogen removal in MABAR. Therefore, the change of nitrogen removal route further gave MABAR excellent adaptability and impact resistance to address wastewater with different COD/N ratios, which is conducive to its wide application.

Comparative Effects of Different Light Sources on the Production of Key Secondary Metabolites in Plants In Vitro Cultures

Plant secondary metabolites are known to have a variety of biological activities beneficial to human health. They are becoming more popular as a result of their unique features and account for a major portion of the pharmacological industry. However, obtaining secondary metabolites directly from wild plants has substantial drawbacks, such as taking a long time, posing a risk of species extinction owing to over-exploitation, and producing a limited quantity. Thus, there is a paradigm shift towards the employment of plant tissue culture techniques for the production of key secondary metabolites in vitro. Elicitation appears to be a viable method for increasing phytochemical content and improving the quality of medicinal plants and fruits and vegetables. In vitro culture elicitation activates the plant's defense response and increases the synthesis of secondary metabolites in larger proportions, which are helpful for therapeutic purposes. In this respect, light has emerged as a unique and efficient elicitor for enhancing the in vitro production of pharmacologically important secondary metabolites. Various types of light (UV, fluorescent, and LEDs) have been found as elicitors of secondary metabolites, which are described in this review.

Potential impacts of soil microbiota manipulation on secondary metabolites production in cannabis

BACKGROUND

Cannabis growing practices and particularly indoor cultivation conditions have a great influence on the production of cannabinoids. Plant-associated microbes may affect nutrient acquisition by the plant. However, beneficial microbes influencing cannabinoid biosynthesis remain largely unexplored and unexploited in cannabis production.

OBJECTIVE

To summarize study outcomes on bacterial and fungal communities associated with cannabis using high-throughput sequencing technologies and to uncover microbial interactions, species diversity, and microbial network connections that potentially influence secondary metabolite production in cannabis.

MATERIALS AND METHOD

A mini review was conducted including recent publications on cannabis and their associated microbiota and secondary metabolite production.

RESULTS

In this review, we provide an overview of the potential role of the soil microbiome in production of cannabinoids, and discussed that manipulation of cannabis-associated microbiome obtained through soil amendment interventions of diversified microbial communities sourced from natural forest soil could potentially help producers of cannabis to improve yields of cannabinoids and enhance the balance of cannabidiol (CBD) and tetrahydrocannabinol (THC) proportions.

CONCLUSION

Cannabis is one of the oldest cultivated crops in history, grown for food, fiber, and drugs for thousands of years. Extension of genetic variation in cannabis has developed into wide-ranging varieties with various complementary phenotypes and secondary metabolites. For medical or pharmaceutical purposes, the ratio of CBD to THC is key. Therefore, studying soil microbiota associated with cannabis and its potential impact on secondary metabolites production could be useful when selecting microorganisms as bioinoculant agents for enhanced organic cannabinoid production.

Physiological responses and specific fatty acids composition of Microcystis aeruginosa exposed to total solar radiation and increased temperature

The combined effects of increased temperature and solar ultraviolet radiation (UVR, 280-400 nm) on M. aeruginosa cultures was analyzed in terms of cell abundance, reactive oxygen and nitrogen species (ROS/RNS), antioxidant activity of catalase (CAT), superoxide dismutase (SOD), glutathione S transferase (GST), fatty acids (FA) content and lipid damage. After 12 days exposure to high temperature (29 °C), cells were exposed to solar UVR (4 h). Ultraviolet-B radiation (UVBR, 280-315 nm) resulted into low cell abundance, high ROS/RNS and a significant increase in SOD activity with no changes in GST and a decreased CAT activity at control temperature (26 °C). A significant increase in the analyzed enzymatic antioxidants was observed at 29 °C, as a response to avoid ultraviolet-A radiation (UVAR, 315-400 nm) damage. The relative abundance of ω6 FAs was not affected by UVAR while ω3 FA were highly sensitive at 29 °C but unsaturated fatty acids (UFA) peroxidation did not occur. The differential response in FA to high temperature and UVAR results in differences in lipid damage and antioxidants. It was evident that selected UFAs (mostly ω6) play an important role in high temperature adaptation in addition to enzymatic antioxidant increased activity shifting the temperature growth from 26 to 29 °C. Thus, cell death and UFA damage were avoided at high temperature and low solar irradiance thanks to an increased enzymatic antioxidant activity.

The genome of Draba nivalis shows signatures of adaptation to the extreme environmental stresses of the Arctic

The Arctic is one of the most extreme terrestrial environments on the planet. Here, we present the first chromosome-scale genome assembly of a plant adapted to the high Arctic, Draba nivalis (Brassicaceae), an attractive model species for studying plant adaptation to the stresses imposed by this harsh environment. We used an iterative scaffolding strategy with data from short-reads, single-molecule long reads, proximity ligation data, and a genetic map to produce a 302 Mb assembly that is highly contiguous with 91.6% assembled into eight chromosomes (the base chromosome number). To identify candidate genes and gene families that may have facilitated adaptation to Arctic environmental stresses, we performed comparative genomic analyses with nine non-Arctic Brassicaceae species. We show that the D. nivalis genome contains expanded suites of genes associated with drought and cold stress (e.g., related to the maintenance of oxidation-reduction homeostasis, meiosis, and signaling pathways). The expansions of gene families associated with these functions appear to be driven in part by the activity of transposable elements. Tests of positive selection identify suites of candidate genes associated with meiosis and photoperiodism, as well as cold, drought, and oxidative stress responses. Our results reveal a multifaceted landscape of stress adaptation in the D. nivalis genome, offering avenues for the continued development of this species as an Arctic model plant.

Could Bryophagous Beetles (Coleoptera: Byrrhidae) Help Us Understand Bryophyte Taxonomy? Preferences within the Hypnum cupressiforme Hedw. Species Complex

Intrataxonomic differences in terms of angiosperm suitability for herbivorous insects stem from variables such as plant structure, palatability, and chemistry. It has not yet been elucidated whether these differences also occur in terms of the bryophyte’s suitability to bryophages. Hypnum cupressiforme Hedw. is a morphologically variable moss species frequently inhabited or fed by insects. In this investigation, we offered five morphotypes of H. cupressiforme to two bryophagous species of Byrrhidae (Coleoptera) to reveal whether the intrataxonomic variability affects beetles’ preferences. The morphotypes were offered with preserved and removed spatial structures. There were no significant differences in morphotype preferences when spatial structures were preserved, although during the daytime, the beetles moved from the flat morphotype to the usual and turgid morphotypes. The beetles preferred the turgid morphotype when the spatial structures were removed. The results suggest that the spatial structure variations in the H. cupressiforme complex are accompanied by different chemical, physiological, or microscopic morphological profiles that are recognized by the bryophagous insects. Phylogenetic and epigenetic analyses can reveal multiple differences within the H. cupressiforme complex. Their interconnection with information about the preferences of bryophagous insects can help us to elucidate which of these differences are ecologically relevant.

LED Lighting Strategies Affect Physiology and Resilience to Pathogens and Pests in Eggplant (Solanum melongena L.)

Over the last decade, LED lighting has gained considerable interest as an energy-efficient supplemental light source in greenhouse horticulture that can change rapidly in intensity and spectral composition. Spectral composition not only affects crop physiology but may also affect the biology of pathogens, pests, and their natural enemies, both directly and indirectly through an impact on induced plant resistance. In this study, we investigated the effects of light spectrum against a background of sunlight on growth and development of Solanum melongena. These effects were related to the spectral effects on the establishment of populations of the predatory mite Amblyseius swirskii and plant resilience against the biotrophic fungus powdery mildew, the necrotrophic fungus botrytis, and the herbivorous arthropod Western flower thrips. The effects of a reduced red/far-red (R:FR) ratio were studied under two ratios of red to blue light. Far-red light either was supplied additionally to the photosynthetic photon flux density (PPFD) or partially replaced PPFD, while maintaining total photon flux density (PFD). Effects of white light or additional UV-B light on plant resilience was tested, compared to the reference (5% blue, 5% green, and 90% red light). Plant biomass in the vegetative phase increased when additional far-red light was supplied. Stem length increased with far-red, irrespective of PPFD and the percentage of blue light. In the generative phase, total shoot biomass and fruit fresh weights were higher under additional far-red light, followed by the treatments where far-red partly replaced PPFD. Far-red light increased biomass partitioning into the fruits, at the expense of the leaves. There were no differences in population growth of A. swirskii mites between light treatments, nor did light treatment have an effect on the vertical distribution of these predatory mites in the plants. The treatments with additional far-red light reduced the infection rate of powdery mildew, but increased botrytis infection. These differences might be due to the plant defenses acting against these pathogens evolving from two different regulatory pathways. These results show that positive effects of altered spectral compositions on physiological responses were only moderately compensated by increased susceptibility to fungal pathogens, which offers perspective for a sustainable greenhouse horticulture.

Photodegradation influences litter decomposition rate in a humid tropical ecosystem, Brazil

Solar radiation in general and UV radiation in particular have been recognized to stimulate plant litter decomposition through photochemical mineralization of organic molecules such as lignin and through facilitation of microbial decomposition in dryland ecosystems. However, little is known about how photodegradation may influence decomposition in other ecosystems not subject to moisture limitations and under what conditions photodegradation may be favored. Decomposition in humid tropical ecosystems is a complex process, and it can be influenced by a number of environmental factors that are distinct from arid and semi-arid ecosystems. To assess the mechanisms underlying photodegradation by ultraviolet B (UV-B) radiation in a humid tropical ecosystem, we designed a 300-day field experiment in a tropical site in Brazil with high levels of annual precipitation, compared to arid ecosystems, and exposed litter to three levels of radiation (full sun, UV-B removed, and shade) combined with a biocide treatment. Results show that after nearly one year of exposure, the microbial biomass was not affected by UV-B incidence, and this effect has not yet been fully understood for tropical ecosystems. Modeled using an exponential deceleration equation, the removal of UV-B radiation decelerated the plant litter decomposition rate for the control conditions by 21% compared to litter exposed to full sun. Interestingly, shaded litter exhibited similar mass loss compared to litter exposed to full sun. Furthermore, differences in the decay constant among radiation treatments due to the UV-B effect were independent of lignin loss. Overall, our study suggests that UV-B radiation contributed to plant litter decomposition through carbon losses but had no discernible effect on nitrogen, lignin, or cellulose loss specifically. Importantly, our results demonstrate that photodegradation occurs under humid tropical conditions, and further studies are necessary to examine the mechanisms of carbon loss.

Genome-scale metabolic models of Microbacterium species isolated from a high altitude desert environment

The Atacama Desert is the most arid desert on Earth, focus of important research activities related to microbial biodiversity studies. In this context, metabolic characterization of arid soil bacteria is crucial to understand their survival strategies under extreme environmental stress. We investigated whether strain-specific features of two Microbacterium species were involved in the metabolic ability to tolerate/adapt to local variations within an extreme desert environment. Using an integrative systems biology approach we have carried out construction and comparison of genome-scale metabolic models (GEMs) of two Microbacterium sp., CGR1 and CGR2, previously isolated from physicochemically contrasting soil sites in the Atacama Desert. Despite CGR1 and CGR2 belong to different phylogenetic clades, metabolic pathways and attributes are highly conserved in both strains. However, comparison of the GEMs showed significant differences in the connectivity of specific metabolites related to pH tolerance and CO₂ production. The latter is most likely required to handle acidic stress through decarboxylation reactions. We observed greater GEM connectivity within Microbacterium sp. CGR1 compared to CGR2, which is correlated with the capacity of CGR1 to tolerate a wider pH tolerance range. Both metabolic models predict the synthesis of pigment metabolites (β-carotene), observation validated by HPLC experiments. Our study provides a valuable resource to further investigate global metabolic adaptations of bacterial species to grow in soils with different abiotic factors within an extreme environment.

Combined Effects of UV-B and Drought on Native and Exotic Populations of Verbascum thapsus L

During plant invasions, exotic species have to face new environmental challenges and are affected by interacting components of global change, which may include more stressful environmental conditions. We investigated an invasive species of New Zealand grasslands, commonly exposed to two concomitant and limiting abiotic factors-high levels of ultraviolet-B radiation and drought. The extent to which Verbascum thapsus may respond to these interacting stress factors via adaptive responses was assessed in a greenhouse experiment comprising native German plants and plants of exotic New Zealand origins. Plants from both origins were grown within four treatments resulting from the crossed combinations of two levels of UV-B and drought. Over twelve weeks, we recorded growth, morphological characteristics, physiological responses and productivity. The results showed that drought stress had the strongest effect on biomass, morphology and physiology. Significant effects of UV-B radiation were restricted to variables of leaf morphology and physiology. We found neither evidence for additive effects of UV-B and drought nor origin-dependent stress responses that would indicate local adaptation of native or exotic populations. We conclude that drought-resistant plant species might be predisposed to handle high UV-B levels, but emphasize the importance of setting comparable magnitudes in stress levels when testing experimentally for antagonistic interaction effects between two manipulated factors.

Moving north in China: The habitat of Pedicularis kansuensis in the context of climate change

Pedicularis kansuensis is a poisonous grass and a semi-parasitic plant that has spread rapidly in alpine grasslands in recent years and caused great harm to animal husbandry and the ecological environment. However, little is known about the habitat of P. kansuensis and the key environmental factors that influence its expansion. We assessed the potential impact of climate change on the distribution of P. kansuensis in China under representative concentration pathway (RCP) 2.6 and RCP 8.5 using maximum entropy (MaxEnt) and MigClim for the years 2050 and 2070 and examined key environmental factors affecting P. kansuensis distribution. In total, 118 occurrence points and fourteen selected variables were used for the modeling. The models developed for P. kansuensis showed excellent performance (AUC > 0.9 and TSS > 0.90). The results were as follows. 1) The occupied habitats for P. kansuensis in the four climate scenarios were generally offset in the northward direction. 2) The most important environmental variables influencing the spread of P. kansuensis were altitude, annual precipitation, annual temperature range, precipitation in the warmest quarter and ultraviolet-B radiation seasonality (UVB-2). 3) Under RCP 2.6, the occupied habitat would be increased 0.04% by 2050 and would be increased to 0.51% by 2070. Under RCP 8.5, the average occupied habitat was predicted to increase 0.07% by 2050 and increase to 0.53% by 2070. The increase was relatively higher in the occupied habitats located in the southwestern regions (Sichuan, Xizang and Yunnan) than those in the northwestern regions (Gansu and Xinjiang).

Solar UV Irradiance in a Changing Climate: Trends in Europe and the Significance of Spectral Monitoring in Italy

Review of the existing bibliography shows that the direction and magnitude of the long-term trends of UV irradiance, and their main drivers, vary significantly throughout Europe. Analysis of total ozone and spectral UV data recorded at four European stations during 1996–2017 reveals that long-term changes in UV are mainly driven by changes in aerosols, cloudiness, and surface albedo, while changes in total ozone play a less significant role. The variability of UV irradiance is large throughout Italy due to the complex topography and large latitudinal extension of the country. Analysis of the spectral UV records of the urban site of Rome, and the alpine site of Aosta reveals that differences between the two sites follow the annual cycle of the differences in cloudiness and surface albedo. Comparisons between the noon UV index measured at the ground at the same stations and the corresponding estimates from the Deutscher Wetterdienst (DWD) forecast model and the ozone monitoring instrument (OMI)/Aura observations reveal differences of up to 6 units between individual measurements, which are likely due to the different spatial resolution of the different datasets, and average differences of 0.5–1 unit, possibly related to the use of climatological surface albedo and aerosol optical properties in the retrieval algorithms.

Intercomparison of Ground- and Satellite-Based Total Ozone Data Products at Marambio Base, Antarctic Peninsula Region

This study aims to compare the ground-based Brewer spectrophotometer total ozone column measurements with the Dobson spectrophotometer and various satellite overpass data available at Marambio Base during the period 2011–2013. This station provides a unique opportunity to study ozone variability near the edge of the southern polar vortex; therefore, many institutions, such as the National Meteorological Service of Argentina, the Finnish Meteorological Institute and the Czech Hydrometeorological Institute, have been carrying out various scientific activities there. The intercomparison was performed using total ozone column data sets retrieved from the ground-based instruments and from Ozone Monitoring Instrument (OMI)—Total Ozone Mapping Spectrometer (TOMS), OMI–Differential Optical Absorption Spectroscopy (DOAS), Global Ozone Monitoring Experiment 2 (GOME2), and Scanning Imaging Absorption Spectrophotometer for Atmospheric Cartography (SCIAMACHY) satellite observations. To assess the quality of the selected data products, comparisons with reference to the Brewer spectrophotometer single observations were made. The performance of the satellite observational techniques was assessed against the solar zenith angle and effective temperature, as well as against the actual shape of the vertical ozone profiles, which represent an important input parameter for the satellite ozone retrievals. The ground-based Dobson observations showed the best agreement with the Brewer data set (R2 = 1.00, RMSE = 1.5%); however, significant solar zenith angle (SZA) dependency was found. The satellite overpass data confirmed good agreement with the Brewer observations but were, however, overestimated in all cases except for the OMI(TOMS), when the mean bias differed from −0.7 DU in the case of the OMI(TOMS) to 6.4 DU for the SCIAMACHY. The differences in satellite observational techniques were further evaluated using statistical analyses adapted for depleted and non-depleted conditions over the ozone hole period.

The direct observation of the doorway 1nπ* state of methylcinnamate and hydrogen-bonding effects on the photochemistry of cinnamate-based sunscreens

The electronic states and photochemistry including nonradiative decay (NRD) and trans(E) → cis(Z) isomerization of methylcinnamate (MC) and its hydrogen-bonded complex with methanol have been investigated under jet-cooled conditions. S1(1nπ*) and S2(1ππ*) are directly observed in MC. This is the first direct observation of S1(1nπ*) in cinnamate derivatives. Surprisingly, the order of the energies between the nπ* and ππ* states is opposite to substituted cinnamates. TD-DFT and SAC-CI calculations support the observed result and show that the substitution to the benzene ring largely lowers the 1ππ* energy while the effect on 1nπ* is rather small. The S2(ππ*) state lifetime of MC is determined to be equal to or shorter than 10 ps, and the production of the transient T1 state is observed. The T1(ππ*) state is calculated to have a structure in which propenyl C[double bond, length as m-dash]C is twisted by 90°, suggesting the trans → cis isomerization proceeds via T1. The production of the cis isomer is confirmed by low-temperature matrix-isolated FTIR spectroscopy. The effect of H-bonding is examined for the MC-methanol complex. The S2 lifetime of MC-methanol is determined to be 180 ps, indicating that the H-bonding to the C[double bond, length as m-dash]O group largely prohibits the 1ππ* → 1nπ* internal conversion. This lifetime elongation in the methanol complex also describes well a higher fluorescence quantum yield of MC in methanol solution than in cyclohexane, while such a solvent dependence is not observed in para-substituted MC. Determination of the photochemical reaction pathways of MC and MC-methanol will help us to design photofunctional cinnamate derivatives.

No evidence of a protective or cumulative negative effect of UV-B on growth inhibition induced by gamma radiation in Scots pine (Pinus sylvestris) seedlings

Exposure to ambient UV-B radiation may prime protective responses towards various stressors in plants, though information about interactive effects of UV-B and gamma radiation is scarce. Here, we aimed to test whether UV-B exposure could prime acclimatisation mechanisms contributing to tolerance to low-moderate gamma radiation levels in Scots pine seedlings, and concurrently whether simultaneous UV-B and gamma exposure may have an additive adverse effect on seedlings that had previously not encountered either of these stressors. Responses to simultaneous UV-B (0.35 W m-2) and gamma radiation (10.2-125 mGy h-1) for 6 days with or without UV-B pre-exposure (0.35 W m-2, 4 days) were studied across various levels of organisation, as compared to effects of either radiation type. In contrast to UV-B, and regardless of UV-B presence, gamma radiation at ≥42.9 mGy h-1 caused increased formation of reactive oxygen species and reduced shoot length, and reduced root length at 125 mGy h-1. In all experiments there was a gamma dose rate-dependent increase in DNA damage at ≥10.8 mGy h-1, generally with additional UV-B-induced damage. Gamma-induced growth inhibition and gamma- and UV-B-induced DNA damage were still visible 44 days post-irradiation, even at 20.7 mGy h-1, probably due to genomic instability, but this was reversed after 8 months. In conclusion, there was no evidence of a protective effect of UV-B on gamma-induced growth inhibition and DNA damage in Scots pine, and no additive adverse effect of gamma and UV-B radiation on growth in spite of the additional UV-B-induced DNA damage.

Stress and defense responses in plant secondary metabolites production

In the growth condition(s) of plants, numerous secondary metabolites (SMs) are produced by them to serve variety of cellular functions essential for physiological processes, and recent increasing evidences have implicated stress and defense response signaling in their production. The type and concentration(s) of secondary molecule(s) produced by a plant are determined by the species, genotype, physiology, developmental stage and environmental factors during growth. This suggests the physiological adaptive responses employed by various plant taxonomic groups in coping with the stress and defensive stimuli. The past recent decades had witnessed renewed interest to study abiotic factors that influence secondary metabolism during in vitro and in vivo growth of plants. Application of molecular biology tools and techniques are facilitating understanding the signaling processes and pathways involved in the SMs production at subcellular, cellular, organ and whole plant systems during in vivo and in vitro growth, with application in metabolic engineering of biosynthetic pathways intermediates.

A perspective on ecologically relevant plant-UV research and its practical application

Plants perceive ultraviolet-B (UV-B) radiation through the UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8), and initiate regulatory responses via associated signalling networks, gene expression and metabolic pathways. Various regulatory adaptations to UV-B radiation enable plants to harvest information about fluctuations in UV-B irradiance and spectral composition in natural environments, and to defend themselves against UV-B exposure. Given that UVR8 is present across plant organs and tissues, knowledge of the systemic signalling involved in its activation and function throughout the plant is important for understanding the context of specific responses. Fine-scale understanding of both UV-B irradiance and perception within tissues and cells requires improved application of knowledge about UV-attenuation in leaves and canopies, warranting greater consideration when designing experiments. In this context, reciprocal crosstalk among photoreceptor-induced pathways also needs to be considered, as this appears to produce particularly complex patterns of physiological and morphological response. Through crosstalk, plant responses to UV-B radiation go beyond simply UV-protection or amelioration of damage, but may give cross-protection over a suite of environmental stressors. Overall, there is emerging knowledge showing how information captured by UVR8 is used to regulate molecular and physiological processes, although understanding of upscaling to higher levels of organisation, i.e. organisms, canopies and communities remains poor. Achieving this will require further studies using model plant species beyond Arabidopsis, and that represent a broad range of functional types. More attention should also be given to plants in natural environments in all their complexity, as such studies are needed to acquire an improved understanding of the impact of climate change in the context of plant-UV responses. Furthermore, broadening the scope of experiments into the regulation of plant-UV responses will facilitate the application of UV radiation in commercial plant production. By considering the progress made in plant-UV research, this perspective highlights prescient topics in plant-UV photobiology where future research efforts can profitably be focussed. This perspective also emphasises burgeoning interdisciplinary links that will assist in understanding of UV-B effects across organisational scales and gaps in knowledge that need to be filled so as to achieve an integrated vision of plant responses to UV-radiation.

Melatonin increases the performance of Malus hupehensis after UV-B exposure

Melatonin, an evolutionarily conserved molecule, is implicated in numerous physiological processes in plants. To explore the potential roles of melatonin in response to UV-B radiation, we examined the influence of exogenous melatonin on Malus hupehensis Rehd. seedlings under two levels of UV-B radiation. Under UV-B stress, seedlings showed significant reduction in plant growth, biomass production, and root system development. However, 1 μM melatonin solution markedly alleviated these effects, especially at the higher dosage of UV-B radiation. The inhibitory effects of UV-B radiation on photosynthetic parameters, chlorophyll fluorescence parameters, stomatal apertures, chlorophyll levels and leaf membrane damages were also markedly alleviated with melatonin application. Melatonin treatment was also associated with higher activity and expression of genes encoding antioxidant enzymes (ascorbate peroxidase, catalase and peroxidase) and greater decline of H₂O₂ content in leaves exposed to UV-B. Moreover, exogenous melatonin treatment and UV-B stress increased the concentration of endogenous melatonin. The content of several phenolic compounds, including chlorogenic acid, phloridzin and quercetin-3-galactoside, also increased under UV-B stress, and these were further elevated significantly with melatonin addition. This study provides insight into the role(s) of endogenous melatonin in response to UV-B stress, and will facilitate application of exogenous melatonin in agriculture.

Leaf biochemical adjustments in two Mediterranean resprouter species facing enhanced UV levels and reduced water availability before and after aerial biomass removal

Effects of supplemented UV radiation and diminished water supply on the leaf concentrations of phenols and antioxidants of two Mediterranean resprouter species, Arbutus unedo and Quercus suber, were assessed before and after entire aerial biomass removal. Potted seedlings of both species were grown outdoors for 8 months with enhanced UV-A + UV-B, enhanced UV-A or ambient UV, in combination with two watering conditions (field capacity or watering reduction). After this period, all aerial biomass was removed and new shoots (resprouts) developed for a further 8 months under the two treatments. In general, the investment in leaf phenols was substantially greater in A. unedo than in Q. suber, while Q. suber allocated more resources to non-phenolic antioxidants (ascorbate and glutathione). In response to enhanced UV-B radiation, Q. suber leaves rose their UV-screening capacity mainly via accumulation of kaempferols, accompanied by an increased concentration of rutins, being these effects exacerbated under low-watering conditions. Conversely, A. unedo leaves responded to UV-B radiation reinforcing the antioxidant machinery by increasing the overall amount of flavonols (especially quercetins) in seedlings, and of ascorbate and glutathione, along with catalase activity, in resprouts. Nevertheless, UV effects on the amount/activity of non-phenolic antioxidants of A. unedo resprouts were modulated by water supply. Indeed, the highest concentration of glutathione was found under the combination of enhanced UV-B radiation and reduced watering, suggesting an enlargement of the antioxidant response in A. unedo resprouts. Different biochemical responses to enhanced UV and drier conditions in seedlings and resprouts of these two species might modulate their competitive interactions in the near future.

Impact of UV-B radiation on the photosystem II activity, pro-/antioxidant balance and expression of light-activated genes in Arabidopsis thaliana hy4 mutants grown under light of different spectral composition

The effect of UV-B irradiation on the photosystem II (PSII) activity, the content of photosynthetic and UV-absorbing pigments (UAPs), activity of antioxidant enzymes such as catalase (CAT) and peroxidase (POD), as well as H₂O₂ content in 25-day-old wild type (WT) and the cryptochrome 1 (Cry1) mutant hy4 of Arabidopsis thaliana Col-0 plants was studied. In addition, expression of photoreceptor genes Cry1, Cry2 and UVR8, photomorphogenetic gene COP1 and transcription factors genes HY5, HYH, the gene of chlorophyll-binding protein of the PSII CAB1 as well as the flavonoid biosynthesis genes CHS, PAL and thylakoid ascorbate peroxidase gene tAPX was examined. It has been shown that UV-B leads to a decrease in the photochemical activity of PSII (F_V/F_M) and the PSII performance index (PI_ABS) of WT plants grown on white (WL) and red (RL) light and also hy4 mutants grown on WL, RL and blue light (BL). In plants grown on BL and WL, the decrease in the PSII photochemical activity was significantly greater in hy4 compared to WT. The PSII of WT plants grown in BL was resistant to UV-B. The UAPs content of hy4 grown on BL and WL was lower than that in WT. The POD and CAT activities of WT grown in BL were significantly higher than in the mutant. In WT and hy4 plants grown in RL, a noticeable difference in these enzymes activity was not found. In both types of plants grown in BL and RL, the expression of photomorphogenetic genes HYH, HY5 markedly increased after UV-B treatment but the expression of the UV-B photoreceptor gene UVR8 was reduced in hy4 grown in BL and RL. It is assumed that reduced resistance of PSII in hy4 plants grown in BL and WL can be associated with low UAPs content as well as lowered POD and CAT activities. In addition, we suggest the lowered expression of UVR8 and COP1 genes caused by Cry1 deficiency leads to a shift of balance of oxidants and antioxidants towards oxidants.

Ultraviolet radiation modulates C:N stoichiometry and biomass allocation in Fagus sylvatica saplings cultivated under elevated CO2 concentration

Under the conditions of ongoing climate change, terrestrial ecosystems will be simultaneously exposed to a permanent rise in atmospheric CO₂ concentration and increasing variability of such environmental factors as temperature, precipitation, and UV radiation. This will result in numerous interactions. The interactive effects caused by exposure to such multiple environmental factors are not yet well understood. We tested the hypotheses that enhanced UV radiation reduces the stimulatory effect of elevated CO₂ concentration on plant biomass production and that it alters biomass allocation in broadleaved European beech (Fagus sylvatica L.) saplings. Our results after 2 years of exposure confirmed interactive effects of CO₂ concentration and UV radiation on biomass production, and particularly on biomass allocation to roots and aboveground biomass. The strongest stimulatory effect of elevated CO₂ on aboveground biomass and roots was found under ambient UV radiation, while both low and high UV doses reduced this stimulation. Nitrogen content in the roots and the distribution of nitrogen among leaves and roots were also significantly affected by interaction of CO₂ concentration and UV radiation. The observed changes in leaf and root C:N stoichiometry were associated with altered morphological traits, and particularly with a change in the proportion of fine roots. As the biomass allocation and especially the proportion of fine roots can play an important role in effective water and nutrient use and acclimation to future climates, it is essential to obtain a deeper understanding of the links between C:N stoichiometry and biomass accumulation.

Interactive effects of ultraviolet radiation and elevated CO2 concentration on photosynthetic characteristics of European beech saplings during the vegetation season

To test the hypothesis that ultraviolet radiation (UV) modulates photosynthetic responses to elevated CO₂ concentration ([CO₂]) in plants, saplings of European beech were grown for two vegetation seasons under ambient (400 ppm) and elevated (700 ppm) atmospheric [CO₂]. From April to November the saplings were exposed to (i) ambient UV radiation, (ii) excluded and (iii) enhanced UV (150% of ambient). Gas-exchange and chlorophyll fluorescence techniques were used throughout the second vegetation season together with biochemical analyses of the amount and activity of the Rubisco enzyme. We found support for the hypothesis that an impact of elevated [CO₂] on photosynthesis is substantially modulated by UV radiation. Moreover, we found that the [CO₂] × UV interaction is changing along the vegetation season: an enhanced UV radiation stimulated a positive effect of elevated [CO₂] on plant photosynthesis at the beginning of the vegetation season (short-term effect), whilst long-term cultivation reduced the stimulatory effect of elevated [CO₂] (a clear down-regulation of photosynthesis). Down-regulation was, however, not found in plants grown under the conditions of excluded UV radiation. We found evidence that the down-regulation of photosynthesis is associated with a complex acclimation at different hierarchical and functional levels, including an acclimation of primary photochemical reactions, carboxylation activity of Rubisco enzyme, and stomatal conductance.

Linkages between stratospheric ozone, UV radiation and climate change and their implications for terrestrial ecosystems

Linkages between stratospheric ozone, UV radiation and climate change: terrestrial ecosystems.

Photoprotection enhanced by red cell wall pigments in three East Antarctic mosses

BACKGROUND

Antarctic bryophytes (mosses and liverworts) are resilient to physiologically extreme environmental conditions including elevated levels of ultraviolet (UV) radiation due to depletion of stratospheric ozone. Many Antarctic bryophytes synthesise UV-B-absorbing compounds (UVAC) that are localised in their cells and cell walls, a location that is rarely investigated for UVAC in plants. This study compares the concentrations and localisation of intracellular and cell wall UVAC in Antarctic Ceratodon purpureus, Bryum pseudotriquetrum and Schistidium antarctici from the Windmill Islands, East Antarctica.

RESULTS

Multiple stresses, including desiccation and naturally high UV and visible light, seemed to enhance the incorporation of total UVAC including red pigments in the cell walls of all three Antarctic species analysed. The red growth form of C. purpureus had significantly higher levels of cell wall bound and lower intracellular UVAC concentrations than its nearby green form. Microscopic and spectroscopic analyses showed that the red colouration in this species was associated with the cell wall and that these red cell walls contained less pectin and phenolic esters than the green form. All three moss species showed a natural increase in cell wall UVAC content during the growing season and a decline in these compounds in new tissue grown under less stressful conditions in the laboratory.

CONCLUSIONS

UVAC and red pigments are tightly bound to the cell wall and likely have a long-term protective role in Antarctic bryophytes. Although the identity of these red pigments remains unknown, our study demonstrates the importance of investigating cell wall UVAC in plants and contributes to our current understanding of UV-protective strategies employed by particular Antarctic bryophytes. Studies such as these provide clues to how these plants survive in such extreme habitats and are helpful in predicting future survival of the species studied.

Signaling Mechanisms Regulating Diverse Plant Cell Responses to UVB Radiation

UVB radiation (290-320 nm) causes diverse effects in plant cells that vary with the fluence rate of exposure. High fluence rates of UVB radiation cause damage to DNA and formation of reactive oxygen species in mitochondria and chloroplasts, which lead to oxidation of membrane proteins and lipids and inhibition of cellular functions. In response to oxidative stress, mitochondrial transmembrane potential dissipates, resulting in cytochrome c release and activation of metacaspases. This leads to the apoptosis-like cell death. The signaling mechanism based on UVB DNA damage includes checkpoint activation, cell-cycle arrest, and finally programmed cell death with characteristic DNA fragmentation and morphological hallmarks typical of apoptotic cells. Recently, it was shown that among the components of this signaling mechanism the transcriptional factor SOG1 (suppressor of gamma response 1) plays a key role in regulation of programmed cell death in plants. In contrast to its damaging effects, UVB radiation at low fluence rates can act as a regulatory signal that is specifically perceived by plants to promote acclimation and survival in sunlight. The protective action of UVB is based on expression of various genes, including those encoding flavonoid synthesis enzymes that provide a UVB-absorbing sunscreen in epidermal tissues and DNA photorepair enzymes. These processes are mediated by the UVB photoreceptor UVR8, which has been recently characterized at the molecular level. Now progress is made in uncovering the UVR8-mediated signaling pathway mechanism in the context of UVB photon perception and revealing the biochemical components of the early stages of light signal transduction. In this review, attention is focused on the achievements in studying these UVB-induced signaling processes.

Abiotic factors affect the recruitment and biomass of perennial grass and evergreen shrub seedlings in denuded areas of Patagonian Monte rangelands

Assessing the ability of key species to cope with environmental stresses in disturbed areas is an important issue for recovery of degraded arid ecosystem. Our objective was to evaluate the effect of soil moisture, exposure to UV radiation, and presence/absence of litter with different chemistry on soil N, recruitment and biomass of seedlings of perennial grass (Poa ligularis and Nassella tenuis) and evergreen shrub species (Atriplex lampa and Larrea divaricata) in denuded areas. We carried out a microcosm experiment with soil blocks (28 cm depth) sowed with seeds of the target species, subjected to different levels of litter type (perennial grass-evergreen shrub mixture, evergreen shrub mixture, and no litter), UV radiation (near ambient and reduced UV), and soil water (high: 15-25% and low 5-15%). Periodically, during 6 months, we assessed soil-N (total and inorganic) at two depths and species seedling recruitment at microcosms. Additionally, emerged seedlings of each species were transplanted to individual pots containing soil and subjected to the same previous factors during 12 months. Then, all plants were harvested and biomass assessed. Only inorganic soil-N at the upper soil varied among treatments increasing with the presence of evergreen shrub litter, exposure to ambient UV, and high soil water. Inorganic soil-N, promoted by near ambient UV and high soil water, had a positive effect on recruitment of perennial grasses and A. lampa. Both litter types promoted the recruitment of perennial grasses. Evergreen shrub litter and high soil water promoted the recruitment of L. divaricata. Seedling biomass of perennial grasses increased with high soil water and reduced UV. Ambient UV had positive or null effects on biomass of evergreen shrub seedlings. High soil water increased biomass of L. divaricata seedlings. We concluded that soil water appeared as the most limiting factor for seedling recruitment of all species whereas inorganic soil N limited the recruitment of the small-seeded perennial grasses and A. lampa. Ambient UV had negative effects on seedling biomass of perennial grasses. These complex relationships among abiotic factors and seed and plant traits should be taken into account when planning management actions after disturbances.