Induced resistance in the indeterminate growth of aspen (<Emphasis Type="Italic">Populus tremuloides</Emphasis>)

Studies of induction in trees have examined rapid induced resistance (RIR) or delayed induced resistance (DIR), but have not examined induction that occurs in leaves produced by indeterminately growing trees subsequent to, but in the same season as, damage. We refer to induction that occurs during this time period as intermediate-delayed induced resistance (IDIR). We assessed the influences of genetic and environmental factors, and their interactions, on temporal and spatial variation in induction and on tradeoffs between induced and constitutive levels of resistance in indeterminately growing saplings of aspen (Populus tremuloides). We utilized a common garden of 12 aspen genotypes experiencing two levels of defoliation and two levels of soil nutrients. We assessed concentrations of phenolic glycosides and condensed tannins in damaged leaf remnants collected 1 week after defoliation to examine rapid and local induction, and in undamaged leaves produced 8 weeks after defoliation to assess intermediate-delayed and systemic induction. In general, tannins showed RIR, while phenolic glycosides expressed IDIR. For both classes of allelochemicals, we found high estimates of broad-sense heritability and genetic variation in both induced and constitutive levels. Genetic variation may be maintained by both direct costs of allelochemicals and by costs of inducibility (phenotypic plasticity). Such costs may drive the tradeoff exhibited between induced and constitutive levels of phenolic glycosides. IDIR may be important in reducing total-season tissue loss by providing augmented resistance against late summer herbivores in trees that have experienced damage earlier in the season. Herbivore-resistant compensatory growth is especially beneficial to young trees growing in competitive environments.     

Induced resistance in the indeterminate growth of aspen (Populus tremuloides)

Studies of induction in trees have examined rapid induced resistance (RIR) or delayed induced resistance (DIR), but have not examined induction that occurs in leaves produced by indeterminately growing trees subsequent to, but in the same season as, damage. We refer to induction that occurs during this time period as intermediate-delayed induced resistance (IDIR). We assessed the influences of genetic and environmental factors, and their interactions, on temporal and spatial variation in induction and on tradeoffs between induced and constitutive levels of resistance in indeterminately growing saplings of aspen (Populus tremuloides). We utilized a common garden of 12 aspen genotypes experiencing two levels of defoliation and two levels of soil nutrients. We assessed concentrations of phenolic glycosides and condensed tannins in damaged leaf remnants collected 1 week after defoliation to examine rapid and local induction, and in undamaged leaves produced 8 weeks after defoliation to assess intermediate-delayed and systemic induction. In general, tannins showed RIR, while phenolic glycosides expressed IDIR. For both classes of allelochemicals, we found high estimates of broad-sense heritability and genetic variation in both induced and constitutive levels. Genetic variation may be maintained by both direct costs of allelochemicals and by costs of inducibility (phenotypic plasticity). Such costs may drive the tradeoff exhibited between induced and constitutive levels of phenolic glycosides. IDIR may be important in reducing total-season tissue loss by providing augmented resistance against late summer herbivores in trees that have experienced damage earlier in the season. Herbivore-resistant compensatory growth is especially beneficial to young trees growing in competitive environments.     

Experimental habitat fragmentation and invertebrate grazing in a herbaceous grassland species

A field experiment was conducted to examine the effects of habitat fragmentation on herbivore damage to individually tagged leaves of Betonica officinalis rosettes. Fragments of different size and corresponding control plots were established at three study sites in nutrient-poor calcareous grasslands in the northern Swiss Jura mountains. Leaf damage was recorded three times over the growing season (late spring, summer and early autumn). Five years after the initiation of the fragmentation, the density of rosettes did not differ between fragments and control plots. The number of leaves per rosette was higher in fragments than in control plots in summer but not in late spring and early autumn. The extent of leaf damage, expressed as proportion of leaf area removed by invertebrate herbivores, increased over the vegetation period. Leaf damage was greater in fragments than in control plots at two study sites, whereas the opposite (less strongly expressed) was found at the third site. Number of species and density (individuals per m²) of potential herbivores (gastropods and grasshoppers) were recorded in all fragments and control plots. Effects of fragmentation on the number of species and densities depended on plot size and differed between gastropods and grasshoppers. Leaf damage in fragments increased with increasing density of gastropods if the third site, which had lowest leaf damage, was excluded. Such a positive relationship was neither found in control plots nor for grasshopper densities. Thus, movement of gastropods in fragments was probably restricted which resulted in increased feeding pressure at least in two sites. However, even if our fragmentation experiment was well designed and replicated, the interpretation of these experimental results remains difficult because there was large site-to-site and seasonal variation.     

Induced responses in three tropical dry forest plant species – direct and indirect effects on herbivory

Induced changes in plant quality are hypothesized to reduce herbivore numbers and subsequent damage to the plant. The resultant decrease in herbivory may be due to direct negative impacts on herbivores, through the reduction in foliage quality as food, or due to indirect effects of plant-induced traits interacting with the third trophic level, increasing predation and parasitism rates on herbivores. The relative importance of induced responses as direct and/or indirect defenses has not been evaluated in natural systems. Moreover, few studies have evaluated the influence of early-season damage on late-season herbivory in natural systems, particularly in the tropics. The presence of induced responses and subsequent impact on folivory as a consequence of early-season damage were evaluated in three plant species ( Croton pseudoniveus , Bursera instabilis and Piper stipulaceum ) in a tropical dry forest in Mexico. A two-factorial experiment was applied to determine if induced responses influenced subsequent herbivory directly, by reducing foliage quality, or indirectly, through their interaction with parasitoids and predatory arthropods. Plants from all three species with reduced early-season damage had higher herbivory rates through the rest of the growing season, compared to plants that were damaged during leaf expansion. Chemical analyses showed that early-season damage induced the production of total phenolics and condensed tannins for C. pseudoniveus and B. instabilis , respectively. The mechanism by which these compounds affected subsequent herbivory was most likely by directly reducing foliage quality as food for herbivores, given that predatory arthropods and parasitoids had no effects on herbivory in this study. I conclude that early-season damage in these three species influenced later-season herbivory through the induction of plant responses that may act to reduce plant quality as food for herbivores.     

Effects of long-term simulated acid rain on a plant–herbivore interaction

Anthropogenic pollution causes oxidative stress in plants and reactive oxygen species (ROS) are diminished by antioxidative enzymes and small molecular antioxidants. Pollution may also affect the performance of plant-eating animals by increasing or decreasing their performance. The effects of pollution cannot be fully understood without knowledge of how pollution affects the interactions with the third trophic level, namely natural enemies and diseases of herbivores. In this study, we examined how long-term (19 yr) acid rain pollution affects (i) the oxidative responses in mountain birch foliage and (ii) the growth and immune responses of autumnal moth larvae. We found that pollution caused a 50% increase (p<0.05) in the peroxidase activities (PODs) in birch leaves whereas polyphenoloxidase (PPO) or catalase (CAT) activities were not affected, suggesting that PODs play an important role in the quenching of the oxidative stress in birches. In polluted trees, phenoloxidases probably acted as antioxidative not prooxidative enzymes, which was shown as positive relations between enzyme activities (PPO, CAT) and larval performance (pupal weights). Although acid rain pollution did not have any direct effect on either pupal weight or the length of larval period, the stronger acid rain treatment reduced slightly (6% in females) the encapsulation response of pupae. A decrease of this magnitude might be too small to have measurable effects on the incidence of moth outbreaks.     

Attracting pollinators and avoiding herbivores: insects influence plant traits within and across years

Perennial plants interact with herbivores and pollinators across multiple growing seasons, and thus may respond to herbivores and pollinators both within and across years. Joint effects of herbivores and pollinators influence plant traits, but while some of the potential interactions among herbivory, pollination, plant size, and plant reproductive traits have been well studied, others are poorly understood. This is particularly true for perennial plants where effects of herbivores and pollinators may manifest across years. Here, we describe two experiments addressing the reciprocal interactions of plant traits with herbivore damage and pollination across 2 years using the perennial plant Chamerion angustifolium. We measured (1) plant responses to manipulation of damage and pollination in the year of treatment and the subsequent season, (2) damage and pollination responses to manipulation of plant size and flowering traits in the year of treatment, and (3) plant-mediated indirect interactions between herbivores and pollinators. We found that plant traits had little effect on damage and pollination, but damage and pollination affected plant traits in both the treatment year and the subsequent year. We found evidence of indirect effects between leaf herbivores and pollinators in both directions; indirect effects of pollinators on leaf herbivores have not been previously demonstrated. Our results indicate that pollen receipt results in shorter plants with fewer stems but does not change flower number, while leaf herbivory results in taller plants with fewer flowers. Together, herbivory and pollination may contribute to intermediate plant height and plants with fewer stems and flowers in our system.     

Colour polymorphism in relation to population dynamics of the leaf beetle, Chrysomela lapponica

We studied colour morph diversity and frequencies of light and dark morphs in non-fluctuating and fluctuating populations of willow feeding leaf beetle Chrysomela lapponica in the Kola Peninsula, NW Russia. Population-specific Shannon–Weaver diversity index positively correlated with dark morph frequencies, indicating that the larger part of colour polymorphism is related with numbers and diversity of dark morphs. Among-population variation in studied characters was not explained by pollution load or predation rates, but depended on the type of the population and the stage of density change in the fluctuating populations: both colour morph diversity and frequency of dark morphs were low in declining post-outbreak populations but equally high in non-fluctuating populations and in fluctuating populations at peak densities. In time-series, both diversity index and frequency of dark morphs decreased with post-outbreak density decline in the fluctuating population, but did not change in the non-fluctuating population. In the experiment, when adults received low quality food (plants from post-outbreak site), mortality of dark morphs during the hibernation was almost doubled relative to the mortality of light morphs, whereas on high quality food the colour morphs demonstrated similar mortality. This may indicate, that decrease in colour polymorphism extent and dark morph frequencies in the declining populations is due to selective mortality of dark morphs imposed by density dependent (induced by heavy herbivore damage during an outbreak) decrease in host-plant quality (delayed inducible resistance, DIR). DIR is known as one of the factors driving herbivore populations, but our result is the first evidence that DIR may act as a factor of natural selection. Dark morphs are not only susceptible to low food quality, but also have smaller size compared to light morphs, and therefore the dark females are presumably less fecund. Thus, decrease in frequency of low-fitness (dark) individuals in post-outbreak populations and accumulation of low-fitness phenotypes at the popu-lation peak may create feedbacks contributing to regulation of density fluctuations in Ch. lapponica.     

Genotoxicity biomarkers in M. galloprovincialis as indicators of marine pollutants

Many substances pollute the marine environment. There is today a growing evidence on the increased risk of disease in marine organisms, especially fish, that inhabit contaminated waters. Different types of tumours have been evidenced in fish and shellfish populations. Different short-term biomarkers are available to predict the impact of carcinogens on marine organisms. Their endpoints are different effects at the molecular and cellular level such as gene mutation, chromosome alteration and induction of DNA damage and repair. We have applied two different assays: alkaline elution to measure DNA single strand breaks and micronucleus assay as an index of a chromosomal damage. In order to select an aquatic organism as an indicator of water pollution by carcinogenic agents, we have focused on the mussel. A program of validation of genotoxicity was conducted in aquarium using DMBA. A time-dependence increase of micronuclei was evident after the exposure to 100 ppb/animal. For alkaline elution the effect was 4 times the level of the controls. Experiments in the fields were conducted on adult specimens of Mytilus gdlloprovincialis collected from natural substrates. Our sampling stations were located in the La Spezia gulf, Ligurian sea. Genotoxic effects were evaluated in gill cells. A significant increment of the two parameters in polluted, in comparison with the unpolluted sites has been observed. High frequencies of micronuclei (the highest value was 42 ± 13 with respect to control value 3 ± 2) were scored in mussels from polluted stations. The extent of DNA damage was also relevant with respect to clastogenic damage as revealed by micronucleus test. The greatest value of K (constant of elution) was 8-fold higher with respect to the value of K obtained in the same tissue of mussel from reference areas. Evidence of DNA damage could reflect a recent pollution status, since DNA strand breaks can be rapidly repaired by different mechanisms. On the contrary animals exposed to clastogenic compounds may exhibit elevated micronucleus frequency long after the exposure has ceased. The evaluation of both parameters could provide information of great significance about the pollution status of the water.     

Evaluation of the field impact of an adventitious herbivore on an invasive plant,yellow toadflax,in Colorado,USA

Although some introduced plants arrive into their new range without their generalist and specialist herbivores, for others, their herbivores arrive prior to, with, or after the introduction of the plant, reestablishing the link between natural enemies and invaders in the introduced range. Research documenting the effects of adventitiously introduced herbivores on their target plants in the introduced range, and the mechanisms by which those effects occur, can provide insight into potential biological weed control. We studied the effects of an accidentally introduced beetle Brachypterolus pulicarius on the growth and reproduction of its host, the invasive plant Linaria vulgaris (yellow toadflax), growing under field conditions across multiple years and sites in western Colorado, USA. We found that feeding by B. pulicarius on L. vulgaris was variable among 3 years (2002–2004) and across eight local sites. Part of the variation in damage was explained by ramet density; sites with greater ramet density experienced a higher proportion of damage. In an observational study across 2 years, damage was positively correlated with estimates of sexual reproduction, ramet growth, and clonal shoot production. However, opposite trends were observed in an experiment; damage by B. pulicarius decreased estimates of sexual reproduction. Differences between the results of the observational and experimental studies were likely driven by selective feeding by B. pulicarius on larger ramets. Nonetheless, the ability of B. pulicarius to control established L. vulgaris population growth remains uncertain under the environmental conditions we studied. In both the observational and experimental study, B. pulicarius did not affect L. vulgaris survival, and we found no evidence that established L. vulgaris populations were seed limited, suggesting that reductions in seeds may not translate into demographic changes in heavily infested populations. Interactions among insect foraging behavior, individual plant responses to damage, and the demographic consequences of seed input may help to explain the varying degrees to which herbivores affect plants and populations in this and other systems.     

Top‐down effects on population dynamics of Eriocrania miners (Lepidoptera) under pollution impact: does an enemy‐free space exist?

In areas disturbed by pollution, populations of herbivorous insects may reach high densities. This study was conducted to test one of the hypotheses attempting to explain this phenomenon – that pollution creates an enemy-free space for herbivores. We monitored the population densities of Eriocrania leaf-mining moths on mountain birch, Betula pubescens subsp. czerepanovii , in the vicinity of the nickel–copper smelter in Monchegorsk (Kola Peninsula, NW Russia) over twelve years (1994–2005) and assessed larval mortality from parasitoids, ants and birds. The mean density (mines/birch leaf area) of Eriocrania populations in severely disturbed habitats (industrial barrens) was about 2.7 times higher, and peak densities 2–4 times higher, than in pristine forests. Temporal population variability (measured as the coefficient of variation of log-transformed densities) increased with an increase in pollution load. The proportion of infested trees was not affected by pollution, but mine distribution among trees was more clumped in the polluted sites. Eriocrania populations in disturbed sites fluctuated independently of each other, whereas populations in forest sites fluctuated in synchrony. Larval mortality caused by parasitoids was lower in disturbed sites only during those years when populations of Eriocrania reached high densities; mortality from ants and birds did not differ between disturbed and undisturbed habitats in either high or low density years. In undisturbed forests the rate of population change correlated negatively with previous-year parasitism, suggesting that parasitoids are the key demographic factor in Eriocrania population dynamics. In the habitats heavily disturbed by pollution no such correlation was found, which means that negative feedback with parasitoids is disrupted: parasitoids fail to follow host population growth, thus creating an enemy-free space for Eriocrania leafminers.     

Decline in topsoil microbial quotient, fungal abundance and C utilization efficiency of rice paddies under heavy metal pollution across South China

Agricultural soils have been increasingly subject to heavy metal pollution worldwide. However, the impacts on soil microbial community structure and activity of field soils have been not yet well characterized. Topsoil samples were collected from heavy metal polluted (PS) and their background (BGS) fields of rice paddies in four sites across South China in 2009. Changes with metal pollution relative to the BGS in the size and community structure of soil microorganisms were examined with multiple microbiological assays of biomass carbon (MBC) and nitrogen (MBN) measurement, plate counting of culturable colonies and phospholipids fatty acids (PLFAs) analysis along with denaturing gradient gel electrophoresis (DGGE) profile of 16S rRNA and 18S rRNA gene and real-time PCR assay. In addition, a 7-day lab incubation under constantly 25°C was conducted to further track the changes in metabolic activity. While the decrease under metal pollution in MBC and MBN, as well as in culturable population size, total PLFA contents and DGGE band numbers of bacteria were not significantly and consistently seen, a significant reduction was indeed observed under metal pollution in microbial quotient, in culturable fungal population size and in ratio of fungal to bacterial PLFAs consistently across the sites by an extent ranging from 6% to 74%. Moreover, a consistently significant increase in metabolic quotient was observed by up to 68% under pollution across the sites. These observations supported a shift of microbial community with decline in its abundance, decrease in fungal proportion and thus in C utilization efficiency under pollution in the soils. In addition, ratios of microbial quotient, of fungal to bacterial and qCO(2) are proved better indicative of heavy metal impacts on microbial community structure and activity. The potential effects of these changes on C cycling and CO(2) production in the polluted rice paddies deserve further field studies.     

Histopathological biomarkers and genotoxicity in gill and liver tissues of Nile tilapia Oreochromis niloticus from a polluted part of the Nile River,Egypt

Fish health is affected by water pollution. Oreochromis niloticus collected during summer 2014 from El-Serw, a polluted site on the Nile River, were compared with fish from a reference site, El-Zamalek. Histopathological changes were detected in gill and liver tissue samples using light and electron microscopy. In addition, the degree of DNA damage was measured using the comet assay. To indicate the severity of water pollution at the two sites, physico-chemical properties and heavy metal concentrations were investigated. Gill damage, including lamellar cell hyperplasia and aneurysm, was observed in the fish samples from the polluted site. The livers of fish from the polluted area showed necrosis and an increase in melanomacrophage centres. Histochemical results confirmed a marked rise of gill mucopolysaccharides and a reduction of carbohydrate stored in hepatocytes. Electron microscopy revealed clear alterations in gill and liver tissue of fish from the polluted site. The comet assay showed highly significant DNA damage in tilapia collected from the polluted site, compared to those from the reference site. Histopathological biomarkers and the comet assay may therefore be sensitive indicators of exposure to mixtures of aquatic pollutants in Nile tilapia.     

Effects of simulated winter browsing on mountain birch foliar chemistry and on the performance of insect herbivores

Winter browsing by mammalian herbivores is known to induce a variety of morphological and physiological changes in plants. Browsing has been suggested to decrease the carbohydrate reserves in woody plants, which might lead to reduced tannin production in leaves during the following summer, and consequently, to increased herbivore damage on leaves. We conducted a clipping experiment with mature mountain birch trees and measured the effects of clipping on birch growth, leaf chemistry and toughness, as well as on the performance of insect herbivores. Leaves grew larger and heavier per unit area in the clipped ramets and had a higher content of proteins than leaves in the control trees. Clipping treatment did not affect the total content of sugars in the leaves (mg g^?1), suggesting that a moderate level of clipping did not significantly reduce the carbohydrate pools of fully‐grown mountain birch trees. Furthermore, the contents of proanthocyanidins (condensed tannins) and gallotannins were slightly higher in the leaves of clipped ramets, contrary to the hypothesis of reduced tannin production. The effects of clipping treatment on leaf and shoot growth and on foliar chemistry were mainly restricted to the clipped ramets, without spreading to untreated ramets within the same tree individual. The effects of clipping on leaf characters varied during the growing season; for instance, leaf toughness in clipped ramets was higher than toughness in control trees and ramets only when leaves were mature. Accordingly, clipping had inconsistent effects on insect herbivores feeding at different times of the growing season. The generally small impact of clipping on herbivore performance suggests that the low intensity of natural browsing at the study area, simulated by our clipping treatment, does not have strong consequences for the population dynamics of insect herbivores on mountain birch via enhanced population growth caused by browsing‐induced changes in food quality.     

Insect herbivory on water mint: you can't get there from here?

Aquatic plants are thought to have fewer herbivore species than their terrestinal counterparts, and possibly to suffer less herbivory I examined herbivory on water mint Mentha aquatica growing in and out of water and tested possible processes determining the observed pattern of leaf damage Plants growing on land had much more herbivore damage than those growing in water The most common herbivore of Mentha at the site (a chrysomelid beetle) showed no p reference for leaves from terrestrial plants over those from aquatic plants Caging aquatic plants to exclude moorhens suggested that these predators were not having a strong effect in removing insect herbivores (though this conclusion is tentative due to low insect numbers) Transplanting aquatic plants to a terrestrial location, while keeping their roots in water, resulted in marked increases in herbivore damage, relative to control aquatic plants The results suggest that the water barrier may prevent effective exploitation of emergent aquatic plants by terrestrial herbivores This may have consequences for observed patterns of herbivore richness on such plants, plant fitness, and a more speculative suggestion, for the mode of reproduction in aquatic plants     

Induction of plant responses to oviposition and feeding by herbivorous arthropods: a comparison

Plants may respond both to feeding and oviposition by herbivorous insects. While responses of plants to feeding damage by herbivores have been studied intensively during the past decades, only a few, but growing number of studies consider the reactions of plants towards egg deposition by herbivorous insects. Plants showing defensive response to oviposition by herbivores do not `wait' until being damaged by feeding, but may instead react towards one of the initial steps of herbivore attack, the egg deposition. Direct plant defensive responses to feeding act directly against the feeding stages of the herbivores. However, a plant may also show direct defensive responses to egg deposition by (a) formation of neoplasms, (b) formation of necrotic tissue (= hypersensitive response), and (c) production of oviposition deterrents. All these plant reactions have directly negative effects on the eggs, hatching larvae, or on the ovipositing females. Indirect plant defensive responses to feeding result in the emission of volatiles (= synomones) that attract predators or parasitoids of the feeding stages. A few recent studies have shown that plants are able to emit volatiles also in response to egg deposition and that these volatiles attract egg parasitoids. Studies on the mechanisms of induction of synomones by egg deposition show several parallels to the mechanisms of induction of plant responses by feeding damage. When considering induced plant defence against herbivores from an evolutionary point of view, the question arises whether herbivores evolved the ability to circumvent or even to exploit the plant's defensive responses. The reactions of herbivores to oviposition induced plant responses are compared with their reactions to feeding induced plant responses.     

Photosynthetic rates and antioxidant enzyme activity ofPlatanus occidentalis growing under two levels of air pollution along the streets of Seoul

We investigated the net photosynthetic rates and antioxidative enzyme activity inPlatanus occidentalis trees growing on two separate streets in Seoul, and representing different degrees of air pollution. In general, concentrations of SO₂, NO₂, and PM10 decreased from May to September. The photosynthetic rate was reduced significantly on the street with higher levels of pollution. Moreover, activities of two antioxidative enzymes, ascorbate peroxidase and glutathione reductase, were greater in May along the more polluted street. These data suggest thatP. occidentalis growing in highly polluted environments may increase their antioxidant enzyme activity to compensate for and to minimize the damage from this stress.     

Genetic diversity increases insect herbivory on oak saplings

A growing body of evidence from community genetics studies suggests that ecosystem functions supported by plant species richness can also be provided by genetic diversity within plant species. This is not yet true for the diversity-resistance relationship as it is still unclear whether damage by insect herbivores responds to genetic diversity in host plant populations. We developed a manipulative field experiment based on a synthetic community approach, with 15 mixtures of one to four oak (Quercus robur) half-sib families. We quantified genetic diversity at the plot level by genotyping all oak saplings and assessed overall damage caused by ectophagous and endophagous herbivores along a gradient of increasing genetic diversity. Damage due to ectophagous herbivores increased with the genetic diversity in oak sapling populations as a result of higher levels of damage in mixtures than in monocultures for all families (complementarity effect) rather than because of the presence of more susceptible oak genotypes in mixtures (selection effect). Assemblages of different oak genotypes would benefit polyphagous herbivores via improved host patch location, spill over among neighbouring saplings and diet mixing. By contrast, genetic diversity was a poor predictor of the abundance of endophagous herbivores, which increased with individual sapling apparency. Plant genetic diversity may not provide sufficient functional contrast to prevent tree sapling colonization by specialist herbivores while enhancing the foraging of generalist herbivores. Long term studies are nevertheless required to test whether the effect of genetic diversity on herbivory change with the ontogeny of trees and local adaptation of specialist herbivores.     

Evaluation of DNA damage and mutagenicity induced by lead in tobacco plants

Tobacco (Nicotiana tabacum L. var. xanthi) seedlings were treated with aqueous solutions of lead nitrate (Pb2+) at concentrations ranging from 0.4 mM to 2.4 mM for 24 h and from 25 microM to 200 microM for 7 days. The DNA damage measured by the comet assay was high in the root nuclei, but in the leaf nuclei a slight but significant increase in DNA damage could be demonstrated only after a 7-day treatment with 200 microM Pb2+. In tobacco plants growing for 6 weeks in soil polluted with Pb2+ severe toxic effects, expressed by the decrease in leaf area, and a slight but significant increase in DNA damage were observed. The tobacco plants with increased levels of DNA damage were severely injured and showed stunted growth, distorted leaves and brown root tips. The frequency of somatic mutations in tobacco plants growing in the Pb2+-polluted soil did not significantly increase. Analytical studies by inductively coupled plasma optical emission spectrometry demonstrate that after a 24-h treatment of tobacco with 2.4 mM Pb2+, the accumulation of the heavy metal is 40-fold higher in the roots than in the above-ground biomass. Low Pb2+ accumulation in the above-ground parts may explain the lower levels or the absence of Pb2+-induced DNA damage in leaves.     

Productivity differences between dandelion (Taraxacum officinale; Asteraceae) clones from pollution impacted versus non-impacted soils

Common dandelions (Taraxacum officinale Weber, sensu lato; Asteraceae) introduced to North America form an assemblage of asexual (agamospermous), clonal lineages derived from Eurasian mixed sexual and asexual populations. We investigated whether selection for more pollution tolerant clonal lineages occurs at polluted sites and selection for more pollution intolerant lineages occurs at unpolluted sites. We tested the above hypothesis by performing reciprocal greenhouse productivity experiments in which unique dandelion clones (12 clones, identified by DNA fingerprinting, from each site type) sampled from two unpolluted and two polluted (moderately enhanced Cu, Pb and Zn soil concentrations) sites were grown pairwise in both unpolluted (nutrient solution only) and polluted (nutrient solution + Cu, Pb and Zn) media (n?=?48 paired tests for each media type). Dandelion clones from polluted sites produced fewer and smaller leaves, shorter roots and smaller root diameters, reduced shoot and root dry weights, and reduced total biomass compared to clones from unpolluted sites when clones were grown in unpolluted-media (P?≤?0.05). In contrast, clones taken from unpolluted sites were shown to produce significantly fewer and shorter leaves, shorter roots and smaller root diameters, reduced shoot and root dry weights, reduced total biomass, a reduced shoot : root biomass ratio, and have much lower survival compared to clones from polluted sites when both were grown in polluted-media (P?≤?0.05). These results reveal that there was increased selection against unpolluted-site clonal lineages in polluted-media and against polluted-site clonal lineages in unpolluted-media. Across all treatments, clones from unpolluted sites growing in unpolluted-media had the highest proximate measures of fitness. Overall, these findings provide insight into the relationships among anthropogenic environmental contamination and the consequent effects of selective forces acting on dandelion clones and their population genetic architecture.     

Application of in situ cage cultures of phytoplankton for monitoring heavy metal pollution in two Norwegian fjords

A simple apparatus for in situ use of the cage culture technique for growing planktonic algae has been developed and used to follow growth and metal uptake of three diatoms in two Norwegian fjords polluted by heavy metals. Continuous pumping of sea water through a chelating resin and continuous water sampling was used to obtain average values for dissolved and particulate heavy metal content at the various test sites. The metals investigated (zinc, copper, lead, cadmium, and mercury) showed differences in the proportion of dissolved to particulate fractions.The three species of diatoms tested gave systematic growth responses to heavy metal pollution in the moderately polluted fjord; one alga died, one showed reduced growth rate at the more contaminated site compared with those at less polluted sites, while the most tolerant alga was apparently not affected. In the heavily polluted fjord only the most tolerant alga survived, showing decreasing growth rate with increasing pollution.Uptake of heavy metals increased generally with increasing heavy metal content in the sea water. The contents in the algae grown in the most polluted fjord were much higher than those obtained in the less polluted fjord, which were higher than the contents reported for algae from non-contaminated areas.