Rapid evolution towards heavy metal resistance by mountain birch around two subarctic copper-nickel smelters

Adaptations to pollution among long‐lived trees have rarely been documented, possibly because of their long reproductive cycles and the evolutionarily short timescales of anthropogenic pollution. Here, I present the results of a greenhouse experiment that suggest rapid evolutionary adaptation of mountain birch [Betula pubescens subsp. czerepanovii (Orlova) Hämet‐Ahti] to heavy metal (HM) stress around two copper–nickel smelters in NW Russia. The adaptation incurs a cost with reduced performance of adapted seedlings in pristine conditions. The industrial barrens around the studied smelters are extremely high‐stress sites with low seed germination and survival. It is likely that strong natural selection has eliminated all sensitive genotypes within one or two generations, with only the most tolerant individuals persisting and producing adapted seeds in the individual barrens. The results were similar from around both smelters, suggesting parallel evolution towards HM resistance.     

Adaptive traits of wild barley plants of Mediterranean and desert origin

Reciprocal introduction of seeds and seedlings was used to test for local adaptation and to identify a set of co-adapted traits of Mediterranean and desert ecotypes of wild barley Hordeum spontaneum. Evidence for local adaptation was found in seedling introductions into intact environments and from ecotype colonization success in the first generation after seed dispersal. Estimates of fitness were obtained at particular stages of the life cycle (seed, seedling and adult). Experiments that manipulated the environment (vegetation removal, different plant density) demonstrated the intensity and direction of natural selection in different life history episodes, but there was no strong evidence for local adaptation under these circumstances. The observed genetically determined differences between Mediterranean and desert ecotypes can be summarized as the following: reproductive output was higher in desert plants, with smaller seeds than in Mediterranean plants. There was a higher competitive ability of Mediterranean than desert plants. Plants of desert origin had significant reductions in yield when grown in mixed stands with Mediterranean plants; no such effect was observed for plants of Mediterranean origin. Seed germination and seedling survival was lower in seeds of desert origin. This was due to both: genetically determined higher dormancy of desert seeds and a trade-off between no. of seeds and their size (directly related to seed/seedling vigour).     

Differentiation in populations of Hordeum spontaneum Koch along a gradient of environmental productivity and predictability: plasticity in response to water and nutrient stress

Plants from four populations of Hordeum spontaneum originating in distinct environments of Israel were compared for stress induced phenotypic plasticity. The environments ranged along a gradient of increasing rainfall amount and predictability from low (desert) to moderate (semisteppe batha) to high (Mediterranean grassland and mountain, the latter also experiencing frost stress). The plants were exposed to a set of four treatments: no stress (optimum water and nutrients), water, nutrient and both water and nutrient stress. Plants from the four populations (or ecotypes) exhibited different patterns of plasticity in response to the different stresses (water and nutrients) and in different trait categories (reproductive, fitness and resource allocation). The importance of plasticity in response to water stress appears to decrease, and to nutrient stress appears to increase along the increasing rainfall gradient. The mountain ecotype, growing in an area with high potential productivity (amount of rainfall) but experiencing periodic frosts, was the most plastic among ecotypes in resource allocation under both water and nutrient stress, but exhibited low plasticity in other trait categories. In contrast, the desert ecotype had low plasticity in resource allocation under water stress and the lowest plasticity among the four ecotypes in all trait categories in response to nutrient stress. The ecotype originating in Mediterranean grassland, a predictable and most favourable environment, was highly plastic in fitness and allocation traits in response to low nutrient levels which is likely to occur due to competition in productive environment. We discuss the observed differences in ecotype plasticity as part of their environmentally induced adaptive ‘strategies’. We found no support for the hypothesis that plants originating in environments with greater variation and unpredictability are more plastic. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society 2002, 75 , 301–312.     

Invasion of temperate grassland by a subtropical annual grass across an experimental matrix of water stress and disturbance

Abstract. An experimental matrix of water stress and disturbance was superimposed on a Lolium perenne-Trifolium repens grassland using a crossed-gradient design, and the annual subtropical grass Digitaria sanguinalis was introduced into the pasture as seeds and transplanted seedlings. Digitaria plants achieved maximum biomass at high water availability and high disturbance. Digitaria plants grown from transplanted seedlings attained greater biomass further from the conditions of high water availability and high disturbance, compared with those that had grown from seed. The biomass of the temperate species was maximized with high water availability and low to intermediate disturbance conditions. The reproductive effort of Digitaria was maximized under intermediate to high water availability and intermediate to low disturbance. Combinations of water stress and disturbance that gave rise to maximum growth of the temperate and subtropical species were consistent with those predicted by C-S-R theory. Results suggest that processes in the regenerative phase of the plant life cycle were constraining the success of Digitaria in New Zealand grassland. Addition of seed to the soil seed bank would probably be maximized in patches of grassland with high disturbance and water availability; these patches will subsequently act as foci for future invasions by Digitaria.     

Chemical treatment of cereal seed in relation to plant vigour and control of soil fungi

Treating oat seeds not contaminated with any known pathogen of this crop with an organo-mercury preparation (Ceresan) increased seedling vigour only when they were grown in natural or simulated winter conditions with periods of frost. This beneficial effect on vigour was largely confined to seedlings and young plants. The fungicide protected the mesocotyls from contamination or invasion by certain soil-borne fungi normally regarded as saprophytes. Cylindrocarpon radicicola and Fusarium sambucinum were closely associated with discoloured mesocotyls bearing lesions and reduced vigour of untreated plants. Protection from such fungi enabled mesocotyls to grow thicker, and, when seedlings were grown in unsterilised soil and exposed to frost, reduced the number with lesions or discolouration. Thus the ability of the saprophytic soil-borne fungi to cause damage seems to be influenced by environmental conditions.     

Germination characteristics of Rhinanthus minor influence field emergence,competitiveness and potential use in restoration projects

• The facultative root hemi‐parasite Rhinanthus minor is often used in grassland habitat restoration projects to regulate ecosystem structure and function. Its impact on community productivity and diversity as a function of resource supply, sward composition and management has been widely investigated. However, there is a lack of information about the possible influence of seed quality on the efficacy of the hemi‐parasite.
• Ten seed lots from commercial sources were sown in the field and their germination characteristics investigated in the laboratory. Seeds from four lots were also germinated and sown in pots alongside plants of two host species, Lotus corniculatus and Holcus lanatus. Plant establishment, height and flowering density were evaluated for the hemi‐parasite, while plant biomass was measured for both R. minor and its host.
• Two aspects of seed quality influenced the field emergence of seed lots of R. minor, the radicle emergence (%) and the length of the lag period from the beginning of imbibition to germination (mean germination time), which indicates seed vigour. A longer lag period (lower vigour) was associated with higher levels of seedling mortality and lower plant vigour, in terms of plant height and biomass accumulation and was also reflected in the parasitic impact of the seed lots.
• Seed quality, specifically germination and vigour, can influence the establishment, survival, subsequent plant productivity and parasitic impact of R. minor in vegetation restoration projects. Seed quality is discussed as a key factor to consider when predicting the impact of the hemi‐parasite on community productivity and diversity.

     

The effects of seed weight on growth and competitive ability of Rumex acetosella from two successional old-fields

Summary The effects of seed size on growth, biomass allocation and competitive ability of Rumex acetosella plants grown either individually or in competition were studied in two populations (6 months and 15 years old respectively) sampled from a postcultivation successional gradient. For plants grown individually there were highly significant effects of seed weight on growth after 43 days, with a higher relative growth rate (RGR) observed for plants raised from heavier seeds. However at the end of the experiment, seedlings developed from lighter seeds had a RGR 2 times greater than those from heavier seeds. Final biomass of the two types was not significantly different after 73 days of growth. When plants were grown individually, there were only slight differences between populations, but when grown in monocultures of 4 plants per pot, plants from the old population had higher root and leaf biomass per pot whereas those from the young population had a higher reproductive effort per pot. This suggests that a trade-off between allocation to sexual and vegetative reproduction occurs over successional time. In mixtures of light and heavy seeds, plants from light seeds were shorter, had fewer leaves and lower biomass than plants from heavy seeds, which were also taller and produced more dry matter than plants grown from heavy seeds in monoculture. The significant effects of seed weight and population on biomass parameters persisted unit the end of the experiment. Seedlings from heavy seeds were strong competitors: those from the young population grew better in the presence of neighbors than in monoculture and those from the late successional population suppressed the more the growth of their partners. Seedlings from light seeds were subordinate competitors. These results suggest that seedlings from seeds of different sizes benefit from contrasting ecological conditions and that selection acts on reproductive output along successional gradients.     

Mountain birch under multiple stressors – heavy metal‐resistant populations co‐resistant to biotic stress but maladapted to abiotic stress

Stress adaptations often include a trade‐off of weakened performance in nonlocal conditions, resulting in divergent selection, and potentially, genetic differentiation and evolutionary adaptation. Results of a two‐phase (greenhouse and field) common garden experiment demonstrated adaptation of mountain birch (Betula pubescens subsp. czerepanovii) populations from industrially polluted areas of the Kola Peninsula, north‐western Russia, to heavy metals (HM), whereas no adaptations to wind or drought stress were detected in populations from wind‐exposed sites. HM‐adapted seedlings were maladapted to drought but less palatable (co‐resistant) to insect herbivores, even under background HM concentrations. The absence of adaptations to harsh microclimate and the generally high adaptive potential of mountain birch, a critical forest forming tree in subarctic Europe, need to be accounted for in models predicting consequences of human‐driven environmental changes, including the projected climate change.     

Sowing seasons and drying methods during post-harvest influence the seed vigour of soybean (Glycine max (L.) Merr.)

Experiments were conducted to study the influence of sowing seasons and drying methods on the seed vigour of two spring soybean (Glycine max (L.) Merr.) cultivars. Two cultivars, ‘Huachun18’ and ‘Huachun 14’, were sown in three seasons viz., spring, summer and autumn and the harvested seeds were dried using three different methods. The results showed that soybean sown in spring had a higher number of branches per plant, pods per branch and seed weight, and consequently resulted in higher seed yields than that of soybean sown in autumn or summer seasons. Seeds sown in the autumn season had the lowest values of electrical conductivity during seed imbibitions, higher peroxidase (POD) activity in germinated seedlings and lower contamination by the seed-borne fungi on the MS medium, which indirectly improved the seed vigour, which was followed by summer sown seeds. Seeds sown during the spring season resulted in poor seed vigour. In addition, the effect of drying methods on the seed vigour was also clarified. Seeds that hung for four days before threshing and then air-dried had the poorest seed vigour which was determined by germination, electrical conductivity, POD activity and seed borne fungal growth. There was no difference in seed vigour between other methods, i.e. seeds threshed directly at harvest and then air-dried on a bamboo sifter or concrete floor. These results indicated that autumn sowing soybean and the drying method in which seeds were threshed directly at harvest and then air-dried on a bamboo sifter resulted in higher seed vigour.     

The Influence of Seed Size Variation on Seed Germination and Seedling Vigour in Diploid and Tetraploid Dactylis glomerata L.

In this study the effects of seed size variation on germinationand seedling vigour have been investigated within and betweenploidy levels of diploid and related autotetraploid Dactylixglomerata. Rates of seed germination and seedling growth werecompared in two contrasting environments using diploid and tetraploidseeds of equal and also different biomass. Within each ploidylevel, seed biomass had no effect on either the overall percentagenor the rate of germination. In contrast, the comparison ofseeds of equal biomass but differing in ploidy level showedthat seeds from tetraploid plants germinated faster and to ahigher percentage than those from diploid plants. With respectto seedling growth, heavier seeds from the tetraploid genotypesgave seedlings of significantly higher biomass than those fromlighter tetraploid and diploid seeds throughout the 2 monthsof study. Interestingly, seeds of equal biomass but from differentploidy levels produced seedlings more similar than those fromthe extreme seed weight categories. These differences were maintainedin two different environmental conditions. These results suggestthat there is a complex interdependance of seed size and ploidyon seed germination and seedling growth but is not a simpleconsequence of differences in seed size between diploids andtheir related tetraploids.Copyright 1995, 1999 Academic Press Dactylis glomerata, polyploidy, seed size, germination, seedling     

The relative contributions of seed and pollen dispersal to gene flow and genetic diversity in seedlings of a tropical palm

Seed and pollen dispersal shape patterns of gene flow and genetic diversity in plants. Pollen is generally thought to travel longer distances than seeds, but seeds determine the ultimate location of gametes. Resolving how interactions between these two dispersal processes shape microevolutionary processes is a long‐standing research priority. We unambiguously isolated the separate and combined contributions of these two dispersal processes in seedlings of the animal‐dispersed palm Oenocarpus bataua to address two questions. First, what is the spatial extent of pollen versus seed movement in a system characterized by long‐distance seed dispersal? Second, how does seed dispersal mediate seedling genetic diversity? Despite evidence of frequent long‐distance seed dispersal, we found that pollen moves much further than seeds. Nonetheless, seed dispersal ultimately mediates genetic diversity and fine‐scale spatial genetic structure. Compared to undispersed seedlings, seedlings dispersed by vertebrates were characterized by higher female gametic and diploid seedling diversity and weaker fine‐scale spatial genetic structure for female gametes, male gametes and diploid seedlings. Interestingly, the diversity of maternal seed sources at seed deposition sites (N _em) was associated with higher effective number of pollen sources (N _ep), higher effective number of parents (N _e) and weaker spatial genetic structure, whereas seed dispersal distance had little impact on these or other parameters we measured. These findings highlight the importance maternal seed source diversity (N _em) at frugivore seed deposition sites in driving emergent patterns of fine‐scale genetic diversity and structure.     

A butenolide, isolated from smoke, can overcome the detrimental effects of extreme temperatures during tomato seed germination

The butenolide, 3-methyl-2H-furo[2, 3-c]pyran-2-one, is an highly active compound isolated from plant-derived smoke. This compound is known to stimulate seed germination in a wide range of plants akin to smoke or aqueous extracts of smoke. The present study attempted to elucidate the role of the butenolide in overcoming detrimental effects of low and high temperatures on tomato seed germination and seedling growth. The germination percentage followed a parabolic curve for temperatures ranging from 10 to 40°C, with 25°C being the optimum for all treatments. Control seeds showed radicle emergence at two extreme temperatures (10 and 40°C) and seedlings failed to develop further, even upon prolonged incubation. By comparison the butenolide-treated seeds grew into phenotypically normal seedlings at these non-optimum temperatures. The smoke–water-treated seeds had an intermediate response as only a fraction of germinated seed developed into normal seedlings. Seedling vigour indices as well as seedling weight were significantly higher (p ≤ 0.05) for butenolide-treated seeds at all temperatures. Furthermore, seedlings developed in the presence of the butenolide had about a 1:1 correspondence between root and shoot length. Butenolide-treated seeds grew better than the control seeds in the temperature shift experiments. A gradual decline in the vigour index values was recorded with an increased duration of incubation at the extreme temperatures. Results of the present study are very important from an horticultural point of view as they indicate the potential use of the butenolide compound in restoring normal seed germination and seedling establishment in tomato below and above optimum temperatures.     

Overcoming salinity inhibition of sorghum seed germination by hydration-dehydration treatment

Summary Sorghum (Sorghum bicolar (L) Moench cv EA-955 Serena) seeds, subjected or not to hydration-dehydration treatment were planted in distilled water, NaCl, and Na₂SO₄. When seeds were not hydrated-dehydrated the salts inhibited both seed germination and seedling vigour, and caused an increase in the per cent of abnormal seedlings. The salts neither inhibited seed germination nor increased the per cent of abnormal seedlings if the seeds were treated by hydration-dehydration. However, this treatment was not effective in overcoming the inhibitory effect of either NaCl or Na₂SO₄ on seedling vigour. Application of these principles in growing plants under saline environment is discussed.     

Direct and indirect effects of episodic frost on plant growth and reproduction in subalpine wildflowers

Frost is an important episodic event that damages plant tissues through the formation of ice crystals at or below freezing temperatures. In montane regions, where climate change is expected to cause earlier snow melt but may not change the last frost‐free day of the year, plants that bud earlier might be directly impacted by frost through damage to flower buds and reproductive structures. However, the indirect effects of frost mediated through changes in plant–pollinator interactions have rarely been explored. We examined the direct and pollinator‐mediated indirect effects of frost on three wildflower species in southwestern Colorado, USA, Delphinium barbeyi (Ranunculaceae), Erigeron speciosus (Asteraceae), and Polemonium foliosissimum (Polemoniaceae), by simulating moderate (?1 to ?5°C) frost events in early spring in plants in situ. Subsequently, we measured plant growth, and upon flowering measured flower morphology and phenology. Throughout the flowering season, we monitored pollinator visitation and collected seeds to measure plant reproduction. We found that frost had species‐specific direct and indirect effects. Frost had direct effects on two of the three species. Frost significantly reduced flower size, total flowers produced, and seed production of Erigeron. Furthermore, frost reduced aboveground plant survival and seed production for Polemonium. However, we found no direct effects of frost on Delphinium. When we considered the indirect impacts of frost mediated through changes in pollinator visitation, one species, Erigeron, incurred indirect, negative effects of frost on plant reproduction through changes in floral traits and pollinator visitation, along with direct effects. Overall, we found that flowering plants exhibited species‐specific direct and pollinator‐mediated indirect responses to frost, thus suggesting that frost may play an important role in affecting plant communities under climate change.     

Seed size and emergence time within a stand of wild radish (Raphanus raphanistrum L.): the establishment of a fitness hierarchy

Summary To determine the role of seed size in creating adult plants of different reproductive success, individual seedlings were marked and periodically censused in a natural stand of wild radish (Raphanus raphanistrum L.) in Hamden, Connecticut. Maximum cotyledon witdth is a useful field estimator of seed weight in this species, although dramatic variation in the availability of water can modify this relationship. Using maximum cotyledon width as a linear estimate of seed weight showed that an increase in seed weight gives rise to a disproportionately large increase in an individual's total reproductive output. Analysis of covariance demonstrated that reproductive output is influenced more heavily by seed weight (maximum cotyledon width) than by emergence time. Genetic variation for seed size has been maintained in this population, suggesting that selection favoring large seeds during the seedling stage may be counteracted by selection for large numbers of seeds.     

Role of leaf extracts of some medicinal plants in the management of fungal diseases of okra (Abelmoschus esculentus (L.) Moench)

In order to manage the fungal pathogens in okra, seeds of variety Arka Anamika were subjected to soaking treatment with the aqueous leaf extracts of Coleus aromaticus, Adathoda vesica, Vitex negundo, Solanum nigrum, Leucas aspera, Ocimum sanctum and Catharanthus roseus. Among the extracts used, C. aromaticus, V. negundo extracts were found superior in reducing the incidence of mycoflora. These leaf extract treatments also resulted in increased seed germination and vigour of the seedlings. Both in green-house and field conditions also these extracts were proved their efficient in the enhancement of biomass, number of leaves, number of seeds per fruit, seed density and ascorbic acid content in the raw fruits.     

Germination profiling of lentil genotypes subjected to salinity stress

• Salinity is one of the most severe environmental stresses, negatively affecting productivity of salt‐sensitive crop species. Given that germination is the most critical phase in the plant life cycle, the present study aimed to determine seed germination potential and associated traits under salt stress conditions as a simple approach to identify salt‐tolerant lentil genotypes.
• The genetic material consisted of six lentil genotypes whose adaptation to various agroclimatic conditions is not well elucidated. Salinity stress was applied by addition of NaCl at three different levels of stress, while non‐stressed plants were included as controls. Evaluation of tolerance was performed on the basis of germination percentage, seed water absorbance, root and shoot length, seedling water content, seedling vigour index and number of seedlings with an abnormal phenotype.
• Overall, our findings revealed that salinity stress substantially affects all traits associated with germination and early seedling growth, with the effect of salinity being dependent on the level of stress applied. It is noteworthy, however, that genotypes responded differently to the varying salinity levels. In this context, Samos proved the most salt‐tolerant genotype, indicating its possible use for cultivation under stress conditions.
• In conclusion, the determination of seed germination and early growth potential may be exploited as an efficient strategy to reveal genetic variation in lentil germplasm of unknown tolerance to salinity stress. This approach allows selection of desirable genotypes at early growth stages, thus enabling more efficient application of various breeding methods to achieve stress‐tolerant lentil genotypes.