Abstract: To understand how plants respond to solar UV-B (280-315 nm) and UV-A (315-400 nm) radiation, wavelength specific studies must be performed. For a realistic assessment of these effects seasonal variations that can contribute to UV effects need to be taken into account. This has also implications to studies concerning stratospheric ozone depletion and resulting increased UV-B radiation. To this end, we established a field experiment using plastic films attenuating different parts of the solar UV spectrum. The concentration of individual phenolic compounds during one growing season in leaves of grey alder (Alnus incana) and white birch (Betula pubescens) trees was measured. Our results showed changes in concentration of e.g. hydrolyzable tannins in birch that suggest an effect of UV-A alone and e.g. chlorogenic acids in alder indicate a quadratic effect of UV-B irradiance and both linear and quadratic effect for UV-A in second degree polynomial fits. Further, there was interaction between treatment and sampling time for some individual metabolites, hence the UV response varied during the season. In addition to the UV effects, three temporal patterns emerged in the concentrations of particular groups of phenolics. Possible implications for both sampling methods and timing are discussed. Moreover, our results highlight differences in responses of the two tree species, which are taken to indicate differences in their ecological niche differentiation.
Abstract: Ultraviolet (UV) radiation is an important environmental factor for plant communities; however, plant responses to solar UV are not fully understood. Here, we report differential effects of solar UV-A and UV-B radiation on the expression of flavonoid pathway genes and phenolic accumulation in leaves of Betula pendula Roth (silver birch) seedlings grown outdoors. Plants were exposed for 30 days to six UV treatments created using three types of plastic film. Epidermal flavonoids measured in vivo decreased when UV-B was excluded. In addition, the concentrations of six flavonoids determined by high-performance liquid chromatography-mass spectrometry declined linearly with UV-B exclusion, and transcripts of PAL and HYH measured by quantitative real-time polymerase chain reaction were expressed at lower levels. UV-A linearly regulated the accumulation of quercetin-3-galactoside and quercetin-3-arabinopyranoside and had a quadratic effect on HYH expression. Furthermore, there were strong positive correlations between PAL expression and accumulation of four flavonols under the UV treatments. Our findings in silver birch contribute to a more detailed understanding of plant responses to solar UV radiation at both molecular and metabolite levels.
Abstract: Limitations in the realism of currently available lamps mean that enhancement errors in outdoor experiments simulating UV-B radiation effects of stratospheric ozone depletion can be large. Here, we assess the magnitude of such errors at two Finnish locations, during May and June, under three cloud conditions. First we simulated solar radiation spectra for normal, compared with 10% and 20% ozone depletion, and convoluted the daily integrated solar spectra with eight biological spectral weighting functions (BSWFs) of relevance to effects of UV on plants. We also convoluted a measured spectrum from cellulose-acetate filtered UV-B lamps with the same eight BSWFs. From these intermediate results we calculated the enhancement errors. Differences between locations and months were small, cloudiness had only a minor effect. This assessment was based on the assumption that no extra enhancement compensating for shading of UV radiation by lamp frames is performed. Under this assumption errors between spectra are due to differences in the UV-B effectiveness rather than differences in the UV-A effectiveness. Hence, conclusions about plant growth from past UV-supplementation experiments should be valid. However, interpretation of the response of individual physiological processes is less secure, so results from some field experiments with lamps might need reassessment.
Abstract: Solar ultraviolet (UV)-A and UV-B radiation were excluded from branches of grey alder (Alnus incana) and white birch (Betula pubescens) trees in a field experiment. Leaf litter collected from these trees was used in microcosm experiments under laboratory conditions. The aim was to evaluate the effects of the different UV treatments on litter chemical quality (phenolic compounds, C, N and lignin) and the subsequent effects of these changes on soil fauna and decomposition processes. We measured the decomposition rate of litter, growth of woodlice (Porcellio scaber), soil microbial respiration and abundance of nematodes and enchytraeid worms. In addition, the chemical quality of woodlice feces was analyzed. The exclusion of both UV-A and UV-B had several effects on litter chemistry. Exclusion of UV-B radiation decreased the C content in litter in both tree species. In alder litter, UV exclusion affected concentration of phenolic groups variably, whereas in birch litter there were no significant differences in phenolic compounds. Moreover, further effects on microbial respiration and chemical quality of woodlice feces were apparent. In both tree species, microbial CO(2) evolution was lower in soil with litter produced under exclusion of both UV-A and UV-B radiation when compared to soil with control litter. The N content was higher in the feces of woodlice eating alder litter produced under exclusion of both UV-A and UV-B compared to the control. In addition, there were small changes in the concentration of individual phenolic compounds analyzed from woodlice feces. Our results demonstrate that both UV-A and UV-B alter litter chemistry which in turn affects decomposition processes.
Abstract: In research concerning stratospheric ozone depletion, action spectra are used as biological spectral weighting functions (BSWFs) for describing the effects of UV radiation on plant responses. Our aim was to evaluate the appropriateness of six frequently used BSWFs that differ in effectiveness with increasing wavelength. The evaluation of action spectra was based on calculating the effective UV radiation doses according to 1-2) two formulations of the generalized plant action spectrum, 3) a spectrum for ultraviolet induced erythema in human skin, 4) a spectrum for the accumulation of a flavonol in Mesembryanthemum crystallinum, 5) a spectrum for DNA damage in alfalfa seedlings and 6) the plant growth action spectrum. We monitored effects of UV radiation on the concentration of individual UV absorbing metabolites and chlorophyll concentrations in leaves and growth responses of silver birch (Betula pendula) seedlings. Experiments were conducted outdoors using plastic films attenuating different parts of the UV spectrum. Chlorophyll concentrations and growth were not affected by the UV treatments. The response to UV radiation varied between and within groups of phenolics. In general, the observed responses of phenolic groups and individual flavonoids were best predicted by action spectra extending into the UV-A region with moderate effectiveness.
Abstract: We measured the concentrations of ultraviolet (UV)-absorbing phenolics varying
in response to exclusion of either solar UV-B or both solar UV-A and UV-B radiations in leaves of grey alder (Alnus incana) and white birch (Betula pubescens) trees under field conditions. In alder leaves 20 and in birch leaves 13 different phenolic metabolites were identified. The response to UVexclusion varied between and within groups of phenolics in both tree species. The changes in concentration for some metabolites suggest effects of only UV-A or UV-B, which band being effective depending on the metabolite. For some other metabolites, the results indicate that UV-A and UV-B affect concentrations in the
same direction, while for a few compounds there was evidence suggesting opposite effects of UV-A and UV-B radiation. Finally, the concentration of some phenolics did not significantly respond to solar UV. We observed only minor effects on the summed concentration of all determined phenolic metabolites in alder and birch leaves, thus indicating that measuring only total phenolics concentration may not reveal the effects of radiation. Here, we show that the appropriate biological spectral weighting functions for plant-protective responses against solar UV radiation extend in most cases – but not always – into the UV-A region and more importantly that accumulation of different phenolic metabolites follows different action spectra. This demonstrates under field conditions that some of the implicit assumptions of earlier research simulating ozone
depletion and studying the effects of UVradiation on plant secondary metabolites need to be reassessed.
Abstract: We examined the effects of defoliation concurrently with elevated temperature and CO2 on some chemical and morphological characteristics in the leaves of silver birch seedlings (Betula pendula). We also analyzed the consequent changes in the palatability of leaves for adult blue alder leaf beetles (Agelastica alni). Under the different climatic treatments, the seedlings were subjected to three fertilizer treatments (0 kg, 130 kg and 270 kg N ha−1) and defoliation treatments (0%, 25% and 50% of the total leaf area). In each climatic treatment, fertilization increased the nitrogen content in the leaves, but decreased total concentrations of soluble phenolics, detected by high-performance liquid chromatography (HPLC), and insoluble condensed tannins. Defoliation, both independently and in combination with elevated temperature and CO2, decreased the concentrations of the phenolics. Compared to the intact controls, the leaves of the defoliated seedlings were smaller and tougher. Under elevated temperature, the beetles consumed a smaller amount of the leaves of plants subjected to the high fertilization, while under ambient climatic conditions, fertilization increased the feeding. The total leaf consumption was higher under the ambient climatic conditions than under elevated temperature, elevated CO2 or the combination of elevated temperature and CO2.
Abstract: The activity of polyphenol oxidase (PPO) and guaiacol peroxidase (POD) and the concentrations of chlorophylls, free polyamines and soluble proteins were determined from the leaves of six genotypes of silver birch (Betula pendula Roth) seedlings exposed to short-term elevated carbon dioxide (CO2), temperature (T), ultraviolet-B irradiation (UV-B, 280-315 nm) and their combinations. Results showed that the activity of PPO in the leaves was low but increased by elevated CO2 and elevated T. The POD activity varied between the genotypes due to an interactive effect of CO2 ×UV-B. The soluble proteins were clearly decreased by elevatedCO2, but the level of response varied among the genotypes. The concentrations of chl a and total chlorophylls were lower in the leaves treated with elevated CO2 than in leaves grown at ambient CO2. An interactive effect of CO2 ×UV-B on the chl a/b ratio was found. Elevated T increased chl b concentration and decreased chl a/b ratio. Temperature treatments also caused variation in the concentrations of chl a, chl b and total chlorophylls among the genotypes. Polyamine analyses showed that the concentrations of putrescine were increased and spermine decreased in leaves treated with elevated T. However, the change in putrescine by elevated T was clearer at ambient CO2 than in eCO2 environment (significant effect of T×CO2). In conclusion, the defensive enzymes, photosynthetic pigments, soluble proteins and growth-regulating polyamines in silver birch leaves were not susceptible to enhanced UV-B radiation. In contrast, all the variables responded to elevated T and/or elevated CO2, reflecting the enhancive effects of climate change conditions not only on leaf productivity, but also
on leaf turn-over rate. Most of these climate-driven changes were not regulated by UV-B radiation.
Abstract: Hybridisation between certain willow species is a common feature leading to novel genotypes varying in growth rate and stress tolerance. The objective of this 4-week study was to investigate the effects of decreased watering, enhanced ultraviolet-B irradiation (UV-BBE, 280–315 nm, 7.2 kJ m−2 day−1) and combined decreased watering and enhanced UV-B irradiation on di- and polyamines in the leaves of Salix myrsinifolia and its hybrid with S. myrsinites. Control plantlets were well-watered and exposed to ambient UV-B irradiation (UV-BBE, 3.6 kJ m−2 day−1). HPLC analyses showed that the constitutive concentrations of soluble di- and polyamines varied markedly between S. myrsinifolia and its hybrids. The degree of responses to treatments also varied: in S. myrsinifolia, concentrations of free putrescine were clearly increased by reduced watering, while in the hybrid willow, change in putrescine was less pronounced and not significant. Results also showed that the increase in putrescine in S. myrsinifolia by reduced watering was mitigated by concurrent enhancement of UV-B irradiation. There were no direct UV-B effects on the soluble polyamines.
Abstract: We studied the effects of broad-spectrum light quality on the interaction between the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker and Couch and Scots pine (Pinus sylvestris L.) seedlings and hypocotyl cuttings cultured in vitro. The light sources were cool white (CW), warm white (WW) and red-rich daylight (RD) fluorescent lamps. Inoculation with P. tinctorius enhanced adventitious root formation of the cuttings in all light treatments. Rooting of the inoculated cuttings was highest in WW light (89%), followed by CW (73%) and RD light (66%). During 6 weeks of in vitro culture, rooted cuttings formed only a few lateral roots. The fungus grew over lateral roots, but the Hartig net was absent in all light treatments. In non-inoculated cuttings, neither root formation nor subsequent root growth was affected by light quality. In the seedling experiment, inoculation in the WW treatment resulted in a significantly (P < 0.05) greater number of lateral roots than inoculation in the RD treatment. The percentage of lateral roots covered with fungal hyphae was also highest in WW light (62%), followed by CW (50%) and RD (27%) light. A similar pattern was observed in the intensity of Hartig net formation. We conclude that effects of broad-spectrum light quality on the ectomycorrhizal fungus–root interaction are dependent on the developmental stage of the root.
Abstract: Reflection by waxy or resinous surface structures and hairs, repair reactions of biomolecules and induction of different sheltering components provide the means of plant protection from harmful solar UV-B radiation. Secondary products, especially flavonoids and phenolic acids as defense components are also important in plant tolerance to UV-B, fulfilling the dual role as screens that reduce UV-B penetration in plant tissues, and as antioxidants protecting from damage by reactive oxidant species. Plants are sensitive to UV-B radiation, and this sensitivity can be even more clone-specific than species- specific. The results available in the literature for deciduous trees and shrubs indicate that UV-B radiation may affect several directions in the interaction of woody species with biotic (herbivores) and abiotic (CO, and nutrition) factors depending on the specific interaction in question. These multilevel interactions should have moderate ecological significance via the overall changed performance of woody species and shrubs. (c) 2005 Elsevier Ltd. All rights reserved.
Abstract: The natural variation in quantity and quality of light modifies plant morphology, growth rate and concentration of biochemicals. The aim of two growth-room experiments was to study the combined effects of red (R) and far-red (FR) light and ultraviolet-B (UV-B) radiation on the concentrations of leaf phenolics and growth and morphology of silver birch (Betula pendula Roth) seedlings. Analysis by high-performance liquid chromatography showed that the leaves exposed to supplemental FR relative to R contained higher concentrations of total chlorogenic acids and a cinnamic acid derivative than the leaves treated with supplemental R relative to FR. In contrast, concentration of a flavonoid, quercetin 3-galactoside, was higher in the R + UV-B leaves than in the FR + UV-B leaves. The UV-B induced production of kaempferols, chlorogenic acids and most quercetins were not modified by the R :FR ratio. Growth measurements showed that the leaf petioles and stems of FR seedlings were clearly longer than those of R seedlings, but leaf area was reduced by UV-B radiation. Results of these experiments show that exposure of silver birch seedlings to supplemental FR compared to R leads to fast elongation growth and accumulation of phenolic acids in the leaves.
Abstract: In this study, the effects of elevated ultraviolet-B (UV-B, 280-320 nm) radiation on growth and leaf phenolics were evaluated in clones of dark-leaved willow (Salix myrsinifolia Salisb.) and tea-leaved willow (Salix phylicifolia L.). Willows were raised for one growing season in an irradiation field, where they were exposed either to a constant 50% increase in UV-B-CIE radiation simulating 20-25% ozone depletion or to a small increase in UV-A radiation (320-400 nm). Control willows were grown in the irradiation field under solar radiation (ambient control). Despite the high constitutive concentrations of a UV-absorbing leaf flavonoid, dihydromyricetin, UV-treatments clearly reduced the biomass and height growth of the shoots of one tea-leaved willow clone. In contrast, the growth of three other tea-leaved willow clones showed no significant sensitivity to UV-radiation. Under elevated UV-B radiation, the leaves of these clones were able to accumulate some of the UV-B-absorbing quercetins, myricetins or luteolins. In dark-leaved willows, biomass production and growth were not decreased by UV-exposures, although the concentrations of leaf flavonoids were clearly lower than those in tea-leaved willows; however, in all the dark-leaved willow clones, elevated UV-radiation increased the concentrations of certain quercetins, dihydromyricetin and phenolic acids. Other willow leaf phenolics, i.e. salicylates, condensed tannins and gallic acid derivatives, were either decreased by the UV-treatments or were unaffected. The results indicate that (1) the constitutive level and quality of secondary chemicals in native willow species or clones does not predict their sensitivity to elevated UV-radiation, (2) secondary chemical responses to UV-radiation in willows are more clone-specific than species-specific and (3) the leaves of field-grown willows treated with UV-B radiation accumulate only those phenolics that screen UV-B efficiently.
Abstract: We studied the effects of elevated ultraviolet-B radiation on interactions between insect herbivores and their host plants by exposing two species of phytochemically different willows, Salix myrsinifolia and S. phylicifolia, to a modulated increase in ultraviolet radiation in an outdoor experiment and monitoring the colonisation of insect herbivores on these willows. We examined the effect of increased ultraviolet-B (UV-B) radiation on (1) the quality of willow leaves, (2) the distribution and abundance of insect herbivores feeding on these willows, (3) the resulting amount of damage, and (4) the performance of insect larvae feeding on the exposed plant tissue. Six clones of each of the two willow species were grown in eight blocks for 12 weeks in the UV-B irradiation field. The clones were exposed to a constant 50% increase in UV-Bradiation (simulating 20-25% ozone depletion), to a small increase in UV-A radiation or to ambient solar irradiation. We allowed colonisation on the willows by naturally occurring insects, but also introduced adults of a leaf beetle, Phratora vitellinae, a specialist herbivore on S. myrsinifolia. Increased UV-B radiation did not affect any of the measured indices of plant quality. However, numbers of P. vitellinae on S. myrsinifolia were higher in plants with UV-B treatment compared with UV-A and shade controls. In laboratory tests, growth of the second-instar larva of P. vitellinae was not affected by UV-B treatment of S. myrsinifolia, but was retarded on UV-B treated leaves of S. phylicifolia. In addition, naturally occurring insect herbivores were more abundant on willows exposed to elevated UV-B radiation compared to those grown under control treatments. In spite of the increased abundance of insect herbivores, willows treated with elevated UV-B did not suffer more herbivore damage than willows exposed to ambient solar radiation (shade control). The observed effects of UV-B on herbivore abundance, feeding and growth varied significantly due to spatial variation in environment quality, as indicated by the UV-treatment x block interaction. The results suggest that (1) environmental variation modifies the effects of UV-B radiation on plant-insect interactions and (2) specialist herbivores might be more sensitive to chemical changes in their secondary host plants (S. phylicifolia) than to changes in their primary hosts (S. myrsinifolia).
Abstract: Long-term outdoor experiments were conducted to investigate the effects of elevated ultraviolet-B (UV-B, 280-320 nm) radiation on secondary metabolites (phenolics and terpenoids) and the main soluble sugars (sucrose, raffinose and glucose) in the bark of silver birch (Betula pendula Roth) saplings. Saplings were exposed to a constant 50% increase in erythemal UC irradiance (UV-B-CIE; based on the CIE (International Commission on Illumination) erythernal action spectrum) and a small increase in UV-A radiation (320-400 nm) for three growing seasons in an irradiation field in central Finland. Two control groups were used: saplings exposed to ambient radiation and saplings exposed to slightly increased UV-A radiation. Concentrations of sucrose, raffinose and glucose in bark were higher in UV-treated saplings than in saplings grown in ambient radiation, indicating that stem carbohydrate metabolism was changed by long-term elevated UV radiation. Saplings in the elevated UV-A + UV-B radiation treatment and the UV-A radiation control treatment had significantly increased concentrations of certain UV-absorbing phenolics, such as salidroside, 3,4’-dihydroxypropiophenone-3-glucoside, (+)-catechin and (-)-epicatechin compared with saplings in ambient radiation. In contrast, the radiation treatments had no effect on the non-UV-B-absorbing terpenoids, papyriferic acid and deacetylpapyriferic acid. We conclude that plant parts, in addition to leaves, accumulate specific phenolic UV-filters in response to UV radiation exposure.
Abstract: The effects of long-term elevated UV-B radiation on silver birch (Betula pendula Roth) seedlings were studied over three growing seasons in an outdoor experiment in Finland started 64 days after germination. One group of seedlings was exposed to a constant 50% increase in UV-B-CIE radiation, which corresponds to 20-25% of ozone depletion; another group received a small increase in UV-A radiation and a third (the control group) received ambient solar radiation. Changes in growth appeared during the third growing season; the stems of the UV-B treated seedlings were thinner and their height tended to be shorter compared with that of the control seedlings. In contrast, there were no UV-B effects on biomass, bud burst, bud dry weights, leaf area, rust frequency index or chlorophyll concentrations in any of the summers. During the three-year study, the flavonols were significantly increased by the elevated UV-B only in the first growing season. The responses varied greatly among individual compounds; the most induced were the quercetin glycosides, while the main flavonols, myricetins, were reduced by the UV-A control treatment. In the second summer phenolic acids, such as 3,4’-dihydroxypropiophenone-3-glucoside, neochlorogenic acid and 5-coumarylquinic acid, were increased by the UV-B treatment. In the third year, the constitutive concentrations of phenolics were not affected by the UV-B treatment.
Abstract: This is a study of the impact of increased ultraviolet-B (UV-B) radiation on the secondary chemistry of Salix myrsinifolia (dark-leaved willow). For nearly two decades, the loss of stratospheric ozone above the high latitudes of the Northern Hemisphere has increased UV-B radiation (280–320 nm) over the long-term mean. Willows (Salicaceae) are widely distributed in these northern regions. To determine the effects of increased UV-B radiation on willows, the plantlets of three clones of S. myrsinifolia were grown under ambient (3.6 kJ m-2 day-1) or enhanced (7.18 kJ m-2 day-1) UV-B irradiance. After the 2-week indoor experiment, the concentrations of UV-B-screening phenolics (flavonoids and phenolic acids) and low-UV-B-screening phenolics (salicylates and condensed tannins) in fresh leaves were investigated and the biomass of leaves, stems and roots was determined. As expected, the total amount of flavonoids in willow leaves clearly increased when plantlets were exposed to higher UV-B irradiation. However, the degree of increase of individual compounds varied: luteolin-7-glucoside, monomethyl-monocoumaryl-luteolin-7-glucoside and one myricetin derivative increased significantly, while the apigenin-7-glucuronide increased only slightly. The enhanced UV-B also increased the amount of p-hydroxycinnamic acid derivative. The UV-B effects on other phenolic acids and tannins were minor. In contrast to the other phenolics, the amounts of two salicylates, salicin and saligenin, decreased under enhanced UV-B irradiation. Our results indicate that the concentrations of both UV-B-screening and low-UV-B-screening phenolic compounds in leaves of S.myrsinifolia may vary in response to elevated UV-B radiation. However, while the UV-B protective flavonoids and phenolic acids accumulate during UV-B exposure, the concentrations of certain salicylates decrease.
