Nutrient-rich Habitats Research Articles

Spatial Patterns in the Distribution, Diversity and Abundance of Benthic Foraminifera around Moorea (Society Archipelago, French Polynesia).

Coral reefs are now subject to global threats and influences from numerous anthropogenic sources. Foraminifera, a group of unicellular shelled organisms, are excellent indicators of water quality and reef health. Thus we studied a set of samples taken in 1992 to provide a foraminiferal baseline for future studies of environmental change. Our study provides the first island-wide analysis of shallow benthic foraminifera from around Moorea (Society Archipelago). We analyzed the composition, species richness, patterns of distribution and abundance of unstained foraminiferal assemblages from bays, fringing reefs, nearshore and back- and fore-reef environments. A total of 380 taxa of foraminifera were recorded, a number that almost doubles previous species counts. Spatial patterns of foraminiferal assemblages are characterized by numerical abundances of individual taxa, cluster groups and gradients of species richness, as documented by cluster, Fisher α, ternary plot and Principal Component Analyses (PCA). The inner bay inlets are dominated by stress-tolerant, mostly thin-shelled taxa of Bolivina, Bolivinella, Nonionoides, Elongobula, and Ammonia preferring low-oxygen and/or nutrient-rich habitats influenced by coastal factors such as fresh-water runoff and overhanging mangroves. The larger symbiont-bearing foraminifera (Borelis, Amphistegina, Heterostegina, Peneroplis) generally live in the oligotrophic, well-lit back- and fore-reef environments. Amphisteginids and peneroplids were among the few taxa found in the bay environments, probably due to their preferences for phytal substrates and tolerance to moderate levels of eutrophication. The fringing reef environments along the outer bay are characterized by Borelis schlumbergeri, Heterostegina depressa, Textularia spp. and various miliolids which represent a hotspot of diversity within the complex reef-lagoon system of Moorea. The high foraminiferal Fisher α and species richness diversity in outer bay fringing reefs is consistent with the disturbance-mosaic (microhabitat heterogeneity) hypothesis.Calculations of the FORAM Index (FI), a single metric index to assess reef vitality, indicate that all fore- and most back-reef environments support active carbonate accretion and provide habitat suitability for carbonate producers dependent on algal symbiosis. Lowest suitability values were recorded within the innermost bays, an area where natural and increasing anthropogenic influences continue to impact the reefs. The presence of habitat specific assemblages and numerical abundance values of individual taxa show that benthic foraminifera are excellent recorders of environmental perturbations and good indicators useful in modern and ancient ecological and environmental studies.

Lianas always outperform tree seedlings regardless of soil nutrients: results from a long-term fertilization experiment.

Lianas are a prominent growth form in tropical forests, and there is compelling evidence that they are increasing in abundance throughout the Neotropics. While recent evidence shows that soil resources limit tree growth even in deep shade, the degree to which soil resources limit lianas in forest understories, where they coexist with trees for decades, remains unknown. Regardless, the physiological underpinnings of soil resource limitation in deeply shaded tropical habitats remain largely unexplored for either trees or lianas. Theory predicts that lianas should be more limited by soil resources than trees because they occupy the quick-return end of the "leaf economic spectrum," characterized by high rates of photosynthesis, high specific leaf area, short leaf life span, affinity to high-nutrient sites, and greater foliar nutrient concentrations. To address these issues, we asked whether soil resources (nitrogen, phosphorus, and potassium), alone or in combination, applied experimentally for more than a decade would cause significant changes in the morphology or physiology of tree and liana seedlings in a lowland tropical forest. We found evidence for the first time that phosphorus limits the photosynthetic performance of both trees and lianas in deeply shaded understory habitats. More importantly, lianas always showed significantly greater photosynthetic capacity, quenching, and saturating light levels compared to trees across all treatments. We found little evidence for nutrient x growth form interactions, indicating that lianas were not disproportionately favored in nutrient-rich habitats. Tree and liana seedlings differed markedly for six key morphological traits, demonstrating that architectural differences occurred very early in ontogeny prior to lianas finding a trellis (all seedlings were self-supporting). Overall, our results do not support nutrient loading as a mechanism of increasing liana abundance in the Neotropics. Rather, our finding that lianas always outperform trees, in terms of photosynthetic processes and under contrasting rates of resource supply of macronutrients, will allow lianas to increase in abundance if disturbance and tree turnover rates are increasing in Neotropical forests as has been suggested.

Response of invasive Chromolaena odorata and two coexisting weeds to contrasting irradiance and nitrogen

Chromolaena odorata is a widespread exotic weed in southern China and other regions of the world. To better understand its invasive strategies, we compared leaf pigment contents and gas-exchange traits of the invader with its two coexisting species (native Urena lobata and invasive Bidens pilosa) under combined conditions of irradiance (full, medium, and low) and nitrogen (full, medium, and low) supplies. The chlorophyll (Chl) a+b content of U. lobata was the highest and the Chl a/b ratio of C. odorata was the lowest among the three weed species. In most treatments, leaf pigment, light-saturated photosynthetic rate (P max), and light saturation point (LSP) of all the species increased, while their Chl a/b ratios decreased with the increasing nitrogen. The P max and LSP of U. lobata were greater than those of the coexisting weeds under full irradiance (FI), but significantly declined with the decreasing irradiance. The invasive weeds, especially C. odorata, showed lower P max and LSP under FI, but they showed slight decrease under low irradiance. Compared to U. lobata, C. odorata exhibited the lower light compensation point (LCP) in most treatments, higher LSP under low and medium irradiance, and lower dark respiration rate under FI. In addition, all the three species showed similar responses to different irradiance and nitrogen conditions, mean phenotypic plasticity index (MPPI) of most photosynthetic variables of the two invasive species was lower than that of U. lobata. These results suggested that C. odorata behaved as a facultative shadetolerant weed, being able to grow in moderately sheltered environments; the lower MPPI might be one of the important competitive strategies during its invasion. However, its invasion should be limited to some very shady habitats. In the field, control should be mainly directed against populations growing in the open or nutrient-rich habitats, where its expansion speed could be much faster. Deep shade by intact canopies or luxuriant forests might be an effective barrier against its invasion.

Calliergon megalophyllum rediscovered in the Netherlands after 50 years: comparison to Swedish habitats

The moss Calliergon megalophyllum is rediscovered in the Netherlands after approximately 50 years of absence, in a location different from before: National Park Weerribben-Wieden. This is a Natura 2000 wetland area, and a Dutch hotspot for rich-fen bryophytes. The species was growing in a fen pool. Plant species composition and water chemistry were compared with Swedish samples collected throughout the country. Water chemistry of C. megalophyllum in Sweden was also compared with four other (semi-)aquatic species: C. giganteum, Scorpidium scorpioides, Sarmentypnum trichophyllum and S. exannulatum. The species is characteristic for poorly buffered habitats, but has nevertheless relatively high pH, which makes it sensitive to acidification, especially when atmospheric deposition is high. In the Dutch locality, buffer capacity is maintained by input of base-rich ditch water through small channels in the fen. The data further suggest that, like other Calliergon species, C. megalophyllum is growing in relatively nutrient-rich habitats, especially with respect to P and K. In the Netherlands, plant nutrient concentrations suggest that P is indeed not limiting, which may enhance survival of the species, as P-poor habitats in this country have become very rare.

Development and utility of EST-SSR markers in Ulva prolifera of the South Yellow Sea

Ulva species can grow rapidly in nutrient-rich habitats causing green tides and marine fouling. A more complete understanding of the reasons behind these outbreaks is urgently required. Accordingly, this study attempts to use microsatellite markers based expressed sequence tag (EST) to analyze the genetic variation of several Ulva prolifera populations in the South Yellow Sea of China. Two hundred and thirty-eight SSRs were identified from 8 179 unique ESTs (6 203 newly sequenced and 1 976 downloaded from NCBI database) and 37 primer pairs were successfully designed according to the ESTs; 11 pairs were selected to detect the genetic diversity and relationship of 69 attached U. prolifera samples and 13 free-floating samples collected from coastal and off-coast areas of the South Yellow Sea. The results of cross-species transferability showed that six of the 11 EST-SSR primers could give good amplification in other five Ulva species and the average allele number was 4.67. Genetic variation analysis indicated that all 82 U. prolifera samples were clearly divided and most samples collected from the same site clustered together as a group in the dendrogram tree produced by unweighted pair-group mean analysis (UPGMA) method and the cluster results showed some consistency with the geographical origins. In addition, 13 free-floating samples (except HT-001-2) were grouped as a single clade separated from the attached samples.

Density and age of invasive Robinia pseudoacacia modulate its impact on floodplain forests

The invasion of black locust (Robinia pseudoacacia L.) into nutrient-poor and dry habitats strongly alters resident species composition, species diversity and nutrient availability. However, less is known if its occurrence in more nutrient-rich habitats and dense forests causes similar effects, and if so, how the gradient of stand density and tree age affect soil properties and vegetation composition.We chose riparian forests of the Donau-Auen National Park in Eastern Austria and selected 28 plots which differed in R. pseudoacacia stand density and tree age. Vegetation composition, physical and chemical soil parameters were analyzed. Data analysis was performed using descriptive and bivariate statistics.We found that the content of soil nitrogen, NO3 and carbon increased with black locust density and stand age, respectively, while total C/N ratio appeared to be less affected. While plant diversity (Simpson index) did not show a significant variation neither among Robinia age classes nor along density gradients, some nitrophilous species gained abundance with increased density and some other species with increased age of R. pseudoacacia stands. Only one species (Anemone ranunculoides) became less abundant with Robinia stem density. We argue that these changes in species abundance are primarily due to altered mineral nitrogen availability, but increased radiation intensity under the open canopy of R. pseudoacacia and allelopathic qualities of the tree might also play a role. However, we found evidence that these effects imply certain thresholds and are not linearly scaled.

An invasive clonal plant benefits from clonal integration more than a co-occurring native plant in nutrient-patchy and competitive environments.

Many notorious invasive plants are clonal, however, little is known about the different roles of clonal integration effects between invasive and native plants. Here, we hypothesize that clonal integration affect growth, photosynthetic performance, biomass allocation and thus competitive ability of invasive and native clonal plants, and invasive clonal plants benefit from clonal integration more than co-occurring native plants in heterogeneous habitats. To test these hypotheses, two stoloniferous clonal plants, Alternanthera philoxeroides (invasive), Jussiaea repens (native) were studied in China. The apical parts of both species were grown either with or without neighboring vegetation and the basal parts without competitors were in nutrient- rich or -poor habitats, with stolon connections were either severed or kept intact. Competition significantly reduced growth and photosynthetic performance of the apical ramets in both species, but not the biomass of neighboring vegetation. Without competition, clonal integration greatly improved the growth and photosynthetic performance of both species, especially when the basal parts were in nutrient-rich habitats. When grown with neighboring vegetation, growth of J. repens and photosynthetic performance of both species were significantly enhanced by clonal integration with the basal parts in both nutrient-rich and -poor habitats, while growth and relative neighbor effect (RNE) of A. philoxeroides were greatly improved by clonal integration only when the basal parts were in nutrient-rich habitats. Moreover, clonal integration increased A. philoxeroides's biomass allocation to roots without competition, but decreased it with competition, especially when the basal ramets were in nutrient-rich sections. Effects of clonal integration on biomass allocation of J. repens was similar to that of A. philoxeroides but with less significance. These results supported our hypothesis that invasive clonal plants A. philoxeroides benefits from clonal integration more than co-occurring native J. repens, suggesting that the invasiveness of A. philoxeroides may be closely related to clonal integration in heterogeneous environments.

New Synthesis: Animal Communication Mediated by Microbes: Fact or Fantasy?

New Synthesis: Animal Communication Mediated by Microbes: Fact or Fantasy?

Analysis of Genes and Proteins in Acidithiobacillus ferrooxidans During Growth and Attachment on Pyrite Under Different Conditions

Microbes are able to enhance the sulfide mineral decomposition, which lead to the formation of AMD. Attachment of bacterial cells to the mineral surface is an important process for pyrite oxidation by Acidithiobacillus ferrooxidans. The selective advantage of bacterial adhesion is considered to favor the surface localization of bacterial populations as nutritionally favorable. Environmental factors determine cell accumulation or dissociation of attachment. In our study, the amount of sessile cells increased rapidly during the initial stage of attachment on pyrite. Planktonic cells showed high activity leading to the accumulation of large colonies on the pyrite surface. We found three proteins to be up-regulated significantly. Additionally, by matching the sequences of the three proteins to the Pfam database, we found that they are related to adhesion, pili biosynthesis and movement. When we replaced pyrite with glass to provide an inert surface that abolished electrostatic forces, we found that cell attachment was maintained under nutrient-rich conditions but drastically reduced under conditions of limited nutrients or the presence of the inhibitor homoserinelactone. Our results are consistent with the idea that starvation may lead to inhibition of attachment by an unknown mechanism that allows bacteria to search for nutrient-rich habitats.

Edaphic factors do not govern the ectomycorrhizal specificity of Pisonia grandis (Nyctaginaceae)

Pisonia grandis (Nyctaginaceae), a widespread tree of Pacific coral atolls and islands, displays one of the more restrictive ranges of ectomycorrhizal (ECM) fungus associates among autotrophic plants. Only five ECM fungi are currently known associates; our study adds one. In many habitats, P. grandis is restricted to large seabird colonies where nitrogen and phosphorus inputs in the form of guano are substantial. It has been suggested that the ECM specificity displayed by P. grandis is the result of the unusual nutrient-rich habitat in which P. grandis grows. On Rota, Commonwealth of the Northern Mariana Islands, P. grandis grows in habitats heavily influenced by guano additions and also in upland forests where seabirds do not roost or nest. To test the hypothesis that the ECM specificity displayed by P. grandis is the result of nutrient-related or toxicity-related factors associated with guano inputs, we sampled P. grandis growing in both guano-rich and guano-poor habitats on Rota, Commonwealth of the Northern Mariana Islands. We identified ECM symbionts of P. grandis from both habitats as well as two symbionts of Intsia bijuga (Fabaceae) from nutrient-rich habitats. We identified three ECM symbionts of P. grandis from Rota; all three were found in both guano-rich and guano-poor habitats. No differences in community diversity were detected between guano-rich and guano-poor habitats. We also detected two ECM fungal species associating with I. bijuga but not associating with P. grandis inside guano-rich habitats. From these results, we infer that edaphic factors are not responsible for limiting the ECM community associating with P. grandis to its observed level of specificity.

Gap-, stand-, and landscape-scale factors contribute to poor sugar maple regeneration after timber harvest

Natural regeneration in canopy gaps is a key process affecting long-term dynamics of many forests, including northern hardwood forests. The density and composition of regenerating trees are often highly variable, reflecting sensitivity to a suite of driving factors operating at different scales (e.g., harvest gap to regional landscape), including production of seeds, physical characteristics of gaps and stands, competition with non-tree vegetation, and browsing by animals. Multivariate analyses over broad geographic areas provide insights into the relative effects of these factors and permit exploration of spatial patterns in regeneration. We examined the effects of gap-, stand-, and landscape-scale factors on densities of tree seedlings (<1 m tall) and saplings (1–2 m tall) in 59 selection-harvested northern hardwood stands located across a 4500 km 2 region of Michigan's Upper Peninsula. We used Bayesian multilevel modeling to account for the hierarchical structure of the data and assess uncertainty in parameter estimates. Sugar maple ( Acer saccharum) saplings were absent from 61% of 154 m 2 plots centered in harvest gaps ( n = 347) despite its high shade tolerance and overstory dominance, but densities were high in other gaps. Densities of sugar maple seedlings and/or saplings were negatively associated with a combination of greater stand-scale densities of white-tailed deer ( Odocoileus virginianus), greater gap-scale cover of non-tree vegetation, and lower gap-scale light availability, with deer density having the greatest effect. Densities of unpalatable and commercially less valuable ironwood ( Ostrya virginiana), the second most common regeneration species, were positively related to gap-scale seed-production potential but were unrelated to factors affecting sugar maple. Ironwood tended to replace sugar maple saplings in areas with high deer density. At the landscape scale, densities of sugar maple seedlings and saplings decreased with decreasing latitude and snow depth and increasing winter deer densities. These inverse spatial patterns suggest that deer herbivory can lead to landscape-scale variation in regeneration success. However, the spatial distribution of habitat types (a proxy for soil moisture and nutrient conditions) confound this observation, with higher densities of sugar maple generally located on stands with less nutrient-rich habitat types. Results demonstrate that combinations of factors operating at different scales, and with different relative magnitudes of impact, contribute to high variation in regeneration composition and density following timber harvest. Selection silvicultural practices, as currently applied, do not ensure regeneration of desirable species; practices might require modifications in general (e.g., increasing gap size) and to match them to regionally varying factors like deer density.

The overlooked dwarf males in mosses—Unique among green land plants

Dwarf males occur in several animal groups but are unique to mosses among the green land plants. Mosses, with more than 50% unisexual species and common fertilisation distances in the range of a few decimetres, have evolved various means to cope with potential problems to successfully achieve fertilisation and to ensure sporophyte production and sexually produced diaspores. We explore the abundance of different kinds of extreme female-biased sexual size dimorphism in homocostate pleurocarpous mosses. Based on direct observations and literature information, we investigated the large-scale geographical distribution of this phenomenon, and whether male dwarfism was associated with family position. Almost 60% of 1737 species with information about sexuality are dioecious, and males are known in 769 dioecious species. Dwarf males occur in 178 of these (23%), and are considered obligate in 113 species (63% of 178). We thoroughly examined a subset of 162 species. Among these 72 species (44%) form dwarf males, but only 18 species (25% of 72) produce obligate dwarf males. We conclude that especially facultative male dwarfism is much overlooked among dioecious mosses. The distribution of dioecious species and dwarf males among the latter was related to family membership, but showed little correlation with geographic area. Male dwarfism thus appears useful as a taxonomic character to define bryophyte families. We estimate that between roughly one quarter and almost half of dioecious pleurocarpous moss species exhibit male dwarfism, and the majority of these (75%) form dwarf males facultatively. Male dwarfism in mosses is suggested to have evolved as a result of (1) competing selective pressures of the cytoplasmic and nuclear genomes, (2) competition between the sexes, (3) selection for reduced fertilisation distances, or a combination of these. The associated niche shift of the males may also provide these with a suitably humid and nutrient-rich habitat.

Evolutionary and organismic constraints on the relationship between spacer length and environmental conditions in clonal plants

The rate of lateral spread of clonal plants is considered a plastic trait that responds directly to environmental conditions. However, this response is likely constrained by evolutionary history and other species attributes. Here we ask how the relationships between lateral spread and the distribution of herbaceous plant species in different environments are influenced by the type of spacer (epigeogenous versus hypogeogenous rhizome), its persistence (integrator versus splitter), and the height and phylogeny of the plant. Analysis of spacer length of 367 species from temperate to arctic Europe revealed that other plant characteristics modulate the relationship between spacer length and environmental conditions. While plants with epigeogenous rhizomes, which have usually shorter spacers than hypogeogenous rhizomes, were associated with illuminated habitats, plants with hypogeogenous rhizomes were associated with warm habitats. These relationships were also shown within the specific rhizome type, as within the group of species with epigeogenous rhizomes, those having short spacers were associated with more light. The trend toward long spacers in warm environment was detected within both epigeogenous and hypogeogenous rhizome bearing species. Splitters were found to be associated with wet, nutrient rich habitats irrespective of rhizome type. When plant height was accounted for by using the ratio of spacer length to plant height (L:H) instead of absolute spacer length, no relationship with environmental variables was found until phylogenetic relationships among the species were taken into account. This implies that overall variability in L:H ratio in the dataset masked trends common for different taxonomic groups. Future comparative studies relating particular clonal growth forms or individual traits to environmental conditions should consider the constraints arising from other growth characteristics and evolutionary history of the subject species.

Artificial Seagrass: A Habitat for Marine Fishes

Artificial seagrass plays an important role for the distribution of benthic organisms and fishes. Based on this perspective a study was conducted in the Sepanggar Bay located in the Northern part of Kota Kinabalu, Malaysia from November 2006 to February 2007 to determine the potentiality of artificial seagrass as an alternative habitat for marine fishes. The artificial seagrass area is located approximately 100 m from the coastline at the depth between 6 and 10 m and made up of Dorken Advance Engineer Rubber which was tightened on a square 1 x 3 m metal mat. The sampling process was done by capturing photos and video recording. The picture of the fishes was taken as many as possible to increase the accuracy and precision of fish identification. A total of 497 fish species belong to 17 families were observed in 5 sampling periods throughout the study. Out of 17 families, Pomacentridae was dominant with 25.55% (127 individuals) followed by caesionidae with 22.13% (110 individuals). It was observed that Caesio sp. from a family Caesionidae was dominant genus in the artificial seagrass area, followed by Chromis sp. and Pomacentrus sp. from a family Pomacentridae. Overall Shannon diversity (H’) value of 2.5315 indicates artificial sea grass could play a vital role as a nutrient rich habitat for marine fishes

Termites, vertebrate herbivores, and the fruiting success of Acacia drepanolobium

In African savannas, vertebrate herbivores are often identified as key determinants of plant growth, survivorship, and reproduction. However, plant reproduction is likely to be the product of responses to a suite of abiotic and biotic factors, including nutrient availability and interactions with antagonists and mutualists. In a relatively simple system, we examined the role of termites (which act as ecosystem engineers--modifying physical habitat and creating islands of high soil fertility), vertebrate herbivores, and symbiotic ants, on the fruiting success of a dominant plant, Acacia drepanolobium, in East African savannas. Using observational data, large-scale experimental manipulations, and analysis of foliar N, we found that Acacia drepanolobium trees growing at the edge of termite mounds were more likely to reproduce than those growing farther away, in off-mound soils. Although vertebrate herbivores preferentially used termite mounds as demonstrated by dung deposits, long-term exclusion of mammalian grazers did not significantly reduce A. drepanolobium fruit production. Leaf N was significantly greater in trees growing next to mounds than in those growing farther away, and this pattern was unaffected by exclusion of vertebrates. Thus, soil enrichment by termites, rather than through dung and urine deposition by large herbivores, is of primary importance to fruit production near mounds. Across all mound-herbivore treatment combinations, trees that harbored Crematogaster sjostedti were more likely to fruit than those that harbored one of the other three ant species. Although C. sjostedti is less aggressive than the other ants, it tends to inhabit large, old trees near termite mounds which are more likely to fruit than smaller ones. Termites play a key role in generating patches of nutrient-rich habitat important to the reproductive success of A. drepanolobium in East African savannas. Enhanced nutrient acquisition from termite mounds appears to allow plants to tolerate herbivory and the reduced defense by a relatively ineffective ant partner. Our results underscore the importance of simultaneously examining top-down and bottom-up effects to understand those factors most important to plant reproductive success.

Nutrient Bioaccumulation in Phragmites australis: Management Tool for Reduction of Pollution in the Mar Menor

We studied nutrient removal by Phragmites australis in the Albujon rambla, the main drainage system that discharges into the Mar Menor, a Mediterranean coastal lagoon of high conservation interest, but highly threatened by point and nonpoint pollution derived from tourism and agricultural activities. We measured aerial biomass and N and P concentrations in both aboveground and belowground tissues of common reed during an annual cycle that included two cutting events and two periods of reed growth (one at the end of summer after cutting and another at the beginning of spring, following their natural cycle). The temporal variation of N and P concentrations was related to the phenology of the plant and cutting events. The maximum nutrient concentrations were recorded in young stems in the initial stages of the autumn growing season (35.86 mg N g−1 and 2.38 mg P g−1). The phosphorus dynamics showed evidence of translocation processes related with growth activity, although no evidence of N translocation was found. In November and in summer, when aerial growth ceases because of the hard conditions, the P concentration in rhizomes was higher than in stems, while in spring and in September, the period of maximal growth, the reverse relation was found. The highest total amounts of the two elements in the aboveground biomass (0.54 Tm N ha−1 and 0.25 Tm P ha−1) were reached in July, coinciding with the highest biomass (3.72 kg DW m−2), which then decreased to approximately half in August. Nutrient content in the aboveground tissues was highly dependent on the ammonium and nitrate water concentrations. In addition, the N content was inversely related to the Corg/N of sediments, while the P content was influenced positively by the phosphorous concentration of the water. Common reed of the Albujon rambla corresponds to the assimilation type, adapted to nutrient-rich habitats, which is characterized by a pronounced external N cycle and P internal reserves. Based on the results obtained, we propose a management plan for common reed to help control eutrophication of the Mar Menor lagoon. This would bring forward reed cutting to the beginning of summer, instead of August, coinciding with the time of maximum aerial biomass, greater nutrient retention, and lower risk of strong precipitation.

Apical leaf necrosis as a defence mechanism against pathogen attack: effects of high nutrient availability on onset and rate of necrosis

An outdoor experiment was conducted to increase understanding of apical leaf necrosis in the presence of pathogen infection. Holcus lanatus seeds and Puccinia coronata spores were collected from two adjacent and otherwise similar habitats with differing long-term N fertilization levels. After inoculation, disease and necrosis dynamics were observed during the plant growing seasons of 2003 and 2006. In both years high nutrient availability resulted in earlier disease onset, a higher pathogen population growth rate, earlier physiological apical leaf necrosis onset and a reduced time between disease onset and apical leaf necrosis onset. Necrosis rate was shown to be independent of nutrient availability. The results showed that in these nutrient-rich habitats H. lanatus plants adopted necrosis mechanisms which wasted more nutrients. There was some indication that these necrosis mechanisms were subject to local selection pressures, but these results were not conclusive. The findings of this study are consistent with apical leaf necrosis being an evolved defence mechanism.

Variability of bryophytes and lichens on a forested coastal dune Tõotusemägi in Southwestern Estonia

Variability of bryophytes and lichens on a forested coastal dune Tõotusemägi in Southwestern Estonia Bryophytes and lichens are important in all dry land ecosystems due to their ability to colonize different substrates which are not suitable for vascular plants. They have an important role in vertebrates and invertebrate's food chain and function as a habitat for invertebrates. Nitrogen and carbon cycles in the forest depend greatly on the local bryophyte and lichen flora. The aim of present study was to investigate the frequency and variety of different species of bryophytes and lichens on the forested sand dune Tõotusemägi. The study was carried out on a 183 m long transect running on the western slope of the dune. Identification of bryophyte and lichen species was carried out and zonality of forest ground vegetation was demonstrated. Species were observed on the ground, on litter, on stumps and on trees. On the slope, 26 bryophyte species and 38 lichen species were registered. Dominating bryophyte species were Pleurozium schreberi (Brid.) Mitt., Hylocomium splendens (Hedw.) Schimp., Polytrichum juniperinum Hedw., Polytrichum piliferum Hedw, Dicranum polysetum Sw., Dicranum scoparium Hedw. Dominating lichen species were Cladina rangiferina (L.) Nyl., Cladina arbuscula (Wallr.) Hale &amp; W. L. Culb., Cladonia furcata (Huds.) Schrad, Cetraria islandica (L.) Ach. Dominating species of epiphytic lichens were Hypogymnia physodes (l.) Nyl., Parmelia sulcata Taylor, Pseudevernia furfuracea (L.) Zopf, Parmeliopsis ambigua (Wulfen) Nyl. and Imshaugia aleurites (Ach.) S. L. F. Meyer. On the slope of the dune 12 different ground vegetation zones were distinguished. Bryophyte species characteristic for humid habitats and tolerant to shade were observed on foot of the dune. This may be caused by a stream flowing nearby which creates a more moist and nutrient rich habitat. The top area of the dune is open to direct UV radiation, therefore lichens and only some bryophyte species tolerant to dryness were observed.

Variability of the Molinion meadows in Slovakia

Nine vegetation types were distinguished using cluster analysis within Molinion meadows in Slovakia. Vegetation of cluster 1 occurs on most acidic soils and is characterized by the occurrence of species of the Caricion fuscae alliance and of the Nardus grasslands. Vegetation of cluster 2 is also found on rather acidic soils but in contrast to cluster 1 vegetation it contains species of base-rich sites, such as Betonica officinalis, Galium boreale or Serratula tinctoria. Vegetation of cluster 3 occurs in wet base-rich habitats and often contains species of the Caricion davallianae alliance. Species of dry and Nardus grasslands are typical for vegetation of cluster 4, which is found at the driest sites and is confined to oligotrophic sandy soils. Vegetation of clusters 5 and 6 occurs on moist mesotrophic soils. Their species composition is quite similar, the main difference being that the former includes species-poor releves and the latter includes species-rich releves. Releves of cluster 7 include species of dry grasslands and some ruderal species and represent degraded types of inundated floodplain meadows of the Deschampsion alliance. Vegetation of clusters 8 is characterized by species of the Phragmito-Magnocaricetea class and of the Deschampsion alliance, and occurs in wet nutrient-rich habitats. Vegetation of cluster 9, which usually develops from vegetation of cluster 8 due to decrease in the ground-water table, often contains species of dry grasslands and mesic meadows. Except for releves of clusters 1 and 7, all others can be assigned to the Molinietum caeruleae Koch 1926 association. Cluster 1 corresponds to the Junco effusi-Molinietum caeruleae Tuxen 1954 association. Average Ellenberg indicator values for releves, which were passively projected on the ordination biplot of detrended correspondence analysis, showed that the first ordination axis correlates with nutrients, soil base status and temperature, and second axis with moisture.

Abiotic stresses increase plant regeneration ability

In disturbed habitats, vegetative regeneration is partly ruled by plant reserves and intrinsic growth rates. Under nutrient-limiting conditions, perennial plants tend to exhibit an increased allocation to storage organs. Under mechanically stressful conditions, plants also tend to increase allocation to below-ground biomass and storage organs. We tested whether those stresses acting differently on plants (nutrient level versus mechanical forces) led to similar effect on storage organs and regeneration ability. We measured, for an aquatic plant species, (1) the size and allocation to storage organs (stems) and (2) the regeneration ability of the storage organs. Plant stems were collected in 4 habitats ranked along a nutrient stress gradient, and having encountered null versus significant mechanical stress (flowing water). All stems were placed in similar neutral conditions and left for a period of 6 weeks before measuring their survival and growth. Dry mass allocation to the storage organ (stem) was higher in stressful habitats. Moreover, stress encountered by plants before the experiment significantly affected regeneration: stems of previously stressed plants (i.e. plants that had grown in nutrient-poor or mechanically stressful habitats) survived better than unstressed ones. Stems of plants having encountered mechanical stress before the experiment had increased growth in nutrient-rich habitats but reduced growth in the poorest habitats. These results demonstrate that regeneration could rely on the level of stress previously encountered by plants. Stress could lead to greater regeneration ability following mechanical failure. The possible mechanisms involved in these results are discussed.