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Ecological Implications (ecological + implication)
Selected AbstractsA NEW CELL STAGE IN THE HAPLOID-DIPLOID LIFE CYCLE OF THE COLONY-FORMING HAPTOPHYTE PHAEOCYSTIS ANTARCTICA AND ITS ECOLOGICAL IMPLICATIONS,JOURNAL OF PHYCOLOGY, Issue 5 2010Steffi Gaebler-Schwarz Few members of the well-studied marine phytoplankton taxa have such a complex and polymorphic life cycle as the genus Phaeocystis. However, despite the ecological and biogeochemical importance of Phaeocystis blooms, the life cycle of the major bloom-forming species of this genus remains illusive and poorly resolved. At least six different life stages and up to 15 different functional components of the life cycle have been proposed. Our culture and field observations indicate that there is a previously unrecognized stage in the life cycle of P. antarctica G. Karst. This stage comprises nonmotile cells that range in size from ,4.2 to 9.8 ,m in diameter and form aggregates in which interstitial spaces between cells are small or absent. The aggregates (hereafter called attached aggregates, AAs) adhere to available surfaces. In field samples, small AAs, surrounded by a colony skin, adopt an epiphytic lifestyle and adhere in most cases to setae or spines of diatoms. These AAs, either directly or via other life stages, produce the colonial life stage. Culture studies indicate that bloom-forming, colonial stages release flagellates (microzoospores) that fuse and form AAs, which can proliferate on the bottom of culture vessels and can eventually reform free-floating colonies. We propose that these AAs are a new stage in the life cycle of P. antarctica, which we believe to be the zygote, thus documenting sexual reproduction in this species for the first time. [source] Ecological implications of plants' ability to tell the timeECOLOGY LETTERS, Issue 6 2009Víctor Resco Abstract The circadian clock (the endogenous mechanism that anticipates diurnal cycles) acts as a central coordinator of plant activity. At the molecular and organism level, it regulates key traits for plant fitness, including seed germination, gas exchange, growth and flowering, among others. In this article, we explore current evidence on the effect of the clock for the scales of interest to ecologists. We begin by synthesizing available knowledge on the effect of the clock on biosphere,atmosphere interactions and observe that, at least in the systems where it has been tested, the clock regulates gas exchange from the leaf to the ecosystem level, and we discuss its implications for estimates of the carbon balance. Then, we analyse whether incorporating the action of the clock may help in elucidating the effects of climate change on plant distributions. Circadian rhythms are involved in regulating the range of temperatures a species can survive and affects plant interactions. Finally, we review the involvement of the clock in key phenological events, such as flowering time and seed germination. Because the clock may act as a common mechanism affecting many of the diverse branches of ecology, our ultimate goal is to stimulate further research into this pressing, yet unexplored, topic. [source] Ecological implications of xylem cavitation for several Pinaceae in the Pacific Northern USAFUNCTIONAL ECOLOGY, Issue 5 2000J. Piñol Abstract 1.,Xylem hydraulic properties and vulnerability to cavitation (determined using the air-injection method) were studied in six Pinaceae of the northern Rocky Mountains: Pinus ponderosa, Pseudotsuga menziesii, Larix occidentalis, Pinus contorta, Pinus albicaulis and Abies lasiocarpa. We tested whether species extending into drier habitats exhibited increased resistance to water stress-induced cavitation, and whether there is a trade-off between xylem transport capacity and resistance to cavitation. 2.,At lower elevations the more drought-tolerant P. ponderosa was much less resistant to cavitation than the codominant P. menziesii. Greater vulnerability to cavitation in P. ponderosa was compensated for, at least in part, by increased stomatal control of water loss (inferred from carbon isotope discrimination) and by increased sapwood to leaf area ratios. Similar differences, but less pronounced, were found in codominant species at higher elevations. 3.,Leaf specific hydraulic conductivity was negatively correlated with mean cavitation pressure. When species were separated into pines and non-pines, sapwood specific conductivity and mean cavitation pressure were also negatively correlated within each of the two groups. 4.,Our results indicate that within the evergreen conifers examined, greater resistance to water stress-induced cavitation is not required for survival in more xeric habitats, and that there is a trade-off between xylem conductance and resistance to cavitation. [source] Ecological implications of Fulbe pastoralism in southwestern NigeriaLAND DEGRADATION AND DEVELOPMENT, Issue 5 2003Akin M. Omotayo Abstract The study used a combination of ethno-social surveys and Geographical Information Systems (GIS) to assess 651 pastoral households and their land use under agropastoral production systems in Ogun State, Nigeria. Yields of arable crops on agropastoralists' fields were generally low. Livestock productivity was similar on all parameters to levels in comparable contexts elsewhere across the West African subregion, but generally below possible potentials and on-farm research findings. Pastoral households' activities presently influence between 221,km2 and 523,km2 of land in Ogun State. Pastoral grazing orbits extended beyond administrative boundaries, causing potential conflicts between local crop farmers and agropatoralists. Much of the land-cover has been altered considerably around the areas of pastoral household settlements compared with the situation 20 years ago. It was concluded that a form of intervention was needed that would guarantee sustainability of the land-use system. Copyright © 2003 John Wiley & Sons, Ltd. [source] Ecological implications of biomass and morphotype variations of bacterioplankton: an example in a coastal zone of the Northern Adriatic Sea (Mediterranean)MARINE ECOLOGY, Issue 2 2005Rosabruna La Ferla Abstract This study had the objective of quantifying the variability in abundance, cell volume, morphology and C content of a natural bacterioplankton community in a coastal zone of the North Adriatic Sea during two periods (February and June) of two consequent years (1996 and 1997). We used epifluorescence microscopy with Acridine Orange staining procedures and a microphotographic technique. Low variability in bacterial abundance (range 0.3,3.1 × 105 cells ml,1) occurred between summer and winter periods. Conversely, the cell volume and the calculated carbon content changed greatly with warm and cold periods (ranges: 0.015,0.303 ,m3 and 5.83,42.17 fg C cell,1, respectively). Elongated bacteria were dominant while coccoid cells prevailed only in February 1997. Biomass showed high variability (range 0.12,10.21 ,g C l,1) whilst the abundance did not show noticeable differences among the sampling periods. As a consequence, quantification of bacterial biomass based solely on cell abundance must be considered with caution because the true biomass could depend on variability in cell volumes and morphotypes. [source] Maximum growth rates and possible life strategies of different bacterioplankton groups in relation to phosphorus availability in a freshwater reservoirENVIRONMENTAL MICROBIOLOGY, Issue 9 2006Karel, imek Summary We investigated net growth rates of distinct bacterioplankton groups and heterotrophic nanoflagellate (HNF) communities in relation to phosphorus availability by analysing eight in situ manipulation experiments, conducted between 1997 and 2003, in the canyon-shaped ,ímov reservoir (Czech Republic). Water samples were size-fractionated and incubated in dialysis bags at the sampling site or transplanted into an area of the reservoir, which differed in phosphorus limitation (range of soluble reactive phosphorus concentrations , SRP, 0.7,96 µg l,1). Using five different rRNA-targeted oligonucleotide probes, net growth rates of the probe-defined bacterial groups and HNF assemblages were estimated and related to SRP using Monod kinetics, yielding growth rate constants specific for each bacterial group. We found highly significant differences among their maximum growth rates while insignificant differences were detected in the saturation constants. However, the latter constants represent only tentative estimates mainly due to insufficient sensitivity of the method used at low in situ SRP concentrations. Interestingly, in these same experiments HNF assemblages grew significantly faster than any bacterial group studied except for a small, but abundant cluster of Betaproteobacteria (targeted by the R-BT065 probe). Potential ecological implications of different growth capabilities for possible life strategies of different bacterial phylogenetic lineages are discussed. [source] Community composition and activity of prokaryotes associated to detrital particles in two contrasting lake ecosystemsFEMS MICROBIOLOGY ECOLOGY, Issue 3 2006Charles Lemarchand Abstract The composition, distribution and extracellular enzyme activities of bacteria attached to small (2,50 ,m in size) transparent exopolymer and Coomassie-stained proteinaceous particles (TEP and CSP) were examined in two lakes of different trophic status located in the Massif Central of France. TEP concentrations (104,106 particle per L) were significantly higher in the more productive lake and were significantly related to chlorophyll a concentrations. The majority of TEP and CSP were colonized by bacteria that constituted 2.6% and 7.4% of the total 4,,6-diamidino-2-phenylindole-stained bacteria in lakes Pavin and Aydat, respectively. In both lakes, the composition of particle-associated bacteria was different from that of free-living bacteria, the Betaproteobacteria and Bacteroidetes (i.e. former Cytophaga,Flavobacteria group) being the dominant groups on particles. We also found that 2,5 ,m TEP were more colonized than 2,5 ,m CSP in the two lakes, and that TEP colonization was higher in the less productive lake. Measurements of Leucine aminopeptidase and ,-glucosidase activities in fractionated lake water (0.2,1.2, 1.2,5 and >5 ,m fractions) indicated that proteolytic activity was always higher and that particle-associated bacteria have higher enzymatic activities than free-living bacteria. The glycolytic activities in the 1.2,5 and >5 ,m fractions were related to the abundance of TEP. We conclude that small freshwater detrital organic particles constitute microhabitats with high bacterial activities in pelagic environments and, undoubtedly, present significant ecological implications for the prokaryotic community structure and function in aquatic ecosystems. [source] The use of killer sensitivity patterns for biotyping yeast strains: the state of the art, potentialities and limitationsFEMS YEAST RESEARCH, Issue 6 2007Pietro Buzzini Abstract In recent years molecular techniques have been the most useful tools for the unequivocal identification of undetermined strains at the species level. In many instances, however, a further discrimination at the strain level (biotyping) is required, such as during epidemiological investigations, in which the distribution of pathogenic microorganisms is studied, and for patent protection purposes. Although molecular methods are routinely used also for yeast biotyping, several nonmolecular techniques have been proposed. One of these, the determination of the killer sensitivity pattern (KSP) towards a panel of selected killer toxins has proven to be a good auxiliary method. Despite the plethora of studies published, the potential and limitations of the determination of KSPs have never been critically evaluated. In this review the use of this nonmolecular technique as a biotyping tool is discussed and compared with some currently used DNA-based procedures. In addition, methodological, mechanistic and ecological implications are evaluated. [source] Macrophysiology: large-scale patterns in physiological traits and their ecological implicationsFUNCTIONAL ECOLOGY, Issue 2 2004S. L. Chown First page of article [source] Poleward shifts in breeding bird distributions in New York StateGLOBAL CHANGE BIOLOGY, Issue 8 2009BENJAMIN ZUCKERBERG Abstract Like other regions of the northern hemisphere, the northeastern United States has experienced a general increase in regional temperatures over the past 20 years. Quantifying the ecological implications of these changing temperatures has been severely constrained by a lack of multispecies distributional data by which to compare long-term changes. We used the New York State Breeding Bird Atlas, a statewide survey of 5332 25 km2 blocks surveyed in 1980,1985 and 2000,2005, to test several predictions that the birds of New York State are responding to climate change. Our objective was to use an information-theoretic approach to analyze changes in three geographic range characteristics, the center of occurrence, range boundaries, and states of occurrence to address several predictions that the birds of New York State are moving polewards and up in elevation. As expected, we found all bird species (n=129) included in this analysis showed an average northward range shift in their mean latitude of 3.58 km [Prob(Ha|data)=0.87)]. Past studies have found that northern range boundaries are more likely to be influenced by climatic factors than southern range boundaries. Consequently, we predicted that northward shifts would be more evident in northern as opposed to southern range boundaries. We found, however, that the southern range boundaries of northerly birds moved northward by 11.4 km [n=43, Prob(Ha|data)=0.92], but this pattern was less evident in northern range boundaries of southerly birds. In addition, we found that bird species demonstrated a general shift downhill in their mean elevation, but demonstrated little change in their elevational boundaries. The repeated pattern of a predicted northward shift in bird ranges in various geographic regions of the world provides compelling evidence that climate change is driving range shifts. [source] Avian productivity in urban landscapes: a review and meta-analysisIBIS, Issue 1 2009D. E. CHAMBERLAIN There is an urgent need to thoroughly review and comprehend the effects of urbanization on wildlife in order to understand both the ecological implications of increasing urbanization and how to mitigate its threat to biodiversity globally. We examined patterns in comparative productivity of urban and non-urban passerine birds, using published estimates from paired comparisons, and by reviewing and developing explanations in terms of resources, competitors, predators and other specifically urban environmental factors. The most consistent patterns were for earlier lay dates, lower clutch size, lower nestling weight and lower productivity per nesting attempt in urban landscapes; these were supported by a formal meta-analysis. Nest failure rates did not show consistent patterns across the species considered. We suggest that food availability is a key driver of differences in passerine demography between landscapes. In urban habitats, human-provided food may improve adult condition over winter, leading to earlier lay dates and, in some species, to higher survival and higher breeding densities, but paucity of natural food may lead to lower productivity per nesting attempt. We demonstrate that additional comparative research is needed on a wider range of species, on the effects of natural and human-provided food availability, and on the differences in survival and dispersal between urban and non-urban populations. Importantly, better-targeted research and monitoring is needed in areas that are at greatest threat from urbanization, especially in the developing world. [source] Anthropogenic impacts on lake and stream ecosystems, and approaches to restorationJOURNAL OF APPLIED ECOLOGY, Issue 6 2007MARTIN SØNDERGAARD Summary 1Freshwater ecosystems have long been affected by numerous types of human interventions that have a negative impact on their water quality and ecological state. Fortunately, in most western countries the input of sewage to freshwater systems has been reduced, but hydromorphological alterations, eutrophication-related turbidity and loss of biodiversity remain major problems in many parts of the world. Such impacts prevent the achievement of a high or good ecological state, as defined by the European Water Framework Directive (WFD) or other standards. 2This paper synthesizes and links the findings presented in the seven papers of this special profile, focusing on the effects of anthropogenic stressors on freshwater ecosystems and on how to maintain and restore ecological quality. The papers cover a broad range of research areas and methods, but are all centred on the relationship between dispersal barriers, the connectivity of waterways and the restoration of rivers and lakes. 3The construction of dams and reservoirs disturbs the natural functioning of many streams and rivers and shore-line development around lakes may reduce habitat complexity. New methods demonstrate how reservoirs may have a severe impact on the distribution and connectivity of fish populations, and new techniques illustrate the potential of using graph theory and connectivity models to illustrate the ecological implications. Hydromorphologically degraded rivers and streams can be restored by addition of wood debris, but ,passive' restoration via natural wood recruitment may be preferable. The most cost-effective way to restore streams may also include information campaigns to farmers on best management practices. Removal of zooplanktivorous fish often has marked positive effects on trophic structure in lakes, but there is a tendency to return to turbid conditions after 8,10 years or less unless fish removal is repeated. 4Synthesis and applications. Development of new methods, as well as derivation of more general conclusions from reviewing the effects of previous restoration efforts, are crucial to achieve progress in applied freshwater research. The papers contained in this Special Profile contribute on both counts, as well as illustrating the importance of well-designed research projects and monitoring programmes to record the effects of the interventions. Such efforts are vital if we are to improve our knowledge of freshwater systems and to elaborate the best and most cost-effective recommendations. They may also help in achieving a good ecological state or potential in water bodies by 2015, as demanded by the European WFD. [source] Offshore renewable energy: ecological implications of generating electricity in the coastal zoneJOURNAL OF APPLIED ECOLOGY, Issue 4 2005ANDREW B. GILL Summary 1Global-scale environmental degradation and its links with non-renewable fossil fuels have led to an increasing interest in generating electricity from renewable energy resources. Much of this interest centres on offshore renewable energy developments (ORED). The large scale of proposed ORED will add to the existing human pressures on coastal ecosystems, therefore any ecological costs and benefits must be determined. 2The current pressures on coastal ecology set the context within which the potential impacts (both positive and negative) of offshore renewable energy generation are discussed. 3The number of published peer-review articles relating to renewable energy has increased dramatically since 1991. Significantly, only a small proportion of these articles relate to environmental impacts and none considers coastal ecology. 4Actual or potential environmental impact can occur during construction, operation and/or decommissioning of ORED. 5Construction and decommissioning are likely to cause significant physical disturbance to the local environment. There are both short- and long-term implications for the local biological communities. The significance of any effects is likely to depend on the natural disturbance regime and the stability and resilience of the communities. 6During day-to-day operation, underwater noise, emission of electromagnetic fields and collision or avoidance with the energy structures represent further potential impacts on coastal species, particularly large predators. The wider ecological implications of any direct and indirect effects are discussed. 7Synthesis and applications. This review demonstrates that offshore renewable energy developments will have direct and, potentially, indirect consequences for coastal ecology, with these effects occurring at different scales. Ecologists should be involved throughout all the phases of an ORED to ensure that appropriate assessments of the interaction of single and multiple developments with the coastal environment are undertaken. [source] The effects of neighbouring tree islands on pollinator density and diversity, and on pollination of a wet prairie species, Asclepias lanceolata (Apocynaceae)JOURNAL OF ECOLOGY, Issue 3 2006DEREK R. ARTZ Summary 1The Everglades (Florida, USA) is a mosaic of different habitats. Tropical and temperate trees grow on patches of high ground (tree islands) surrounded by lower elevation wetland communities (marl prairie). 2Tree islands of various sizes provide nesting substrate, larval host plants and floral resources for insect pollinators. Herbaceous plants in the open surrounding wetlands may also depend on these pollinators. 3We investigated pollinator diversity and abundances in both tree island and marl prairie habitats using transect sampling methods and estimated pollination success of the milkweed Asclepias lanceolata, an insect-pollinated marl prairie species, in relation to distance from and size of the closest tree island. 4On a total of 11 bayhead tree islands, we found that insect diversity and abundance were greater on the edge of larger tree islands (20,30 m2) than on smaller tree islands (5,10 m2). Pollinator diversity and abundance in the marl prairie decreased with increasing distance from tree islands. 5Pairs of potted A. lanceolata plants were placed in the marl prairie at distances up to 1000 m from small and large tree islands. Fruit and seed production were highest for plants placed less than 25 m from tree islands and decreased with increasing distance. 6Our results suggest that tree islands are an important source of pollinators for the plants in the tree island and surrounding wetland habitats. 7This landscape-based study illustrates how overall landscape structure affects important biotic interactions, particularly plant,pollinator relationships. Our findings have far-reaching ecological implications for the reproductive success of plants in small, isolated populations that may depend on insect vectors for pollination. [source] ULTRASTRUCTURAL CHARACTERIZATION OF THE LYTIC CYCLE OF AN INTRANUCLEAR VIRUS INFECTING THE DIATOM CHAETOCEROS CF. WIGHAMII(BACILLARIOPHYCEAE) FROM CHESAPEAKE BAY, USA,JOURNAL OF PHYCOLOGY, Issue 4 2009Yoanna Eissler Numerous microalgal species are infected by viruses that have the potential to control phytoplankton dynamics by reducing host populations, preventing bloom formation, or causing the collapse of blooms. Here we describe a virus infecting the diatom Chaetoceros cf. wighamii Brightw. from the Chesapeake Bay. To characterize the morphology and lytic cycle of this virus, we conducted a time-course experiment, sampling every 4 h over 72 h following viral inoculation. In vivo fluorescence began to decline 16 h after inoculation and was reduced to <19% of control cultures by the end of experiment. TEM confirmed infection within the first 8 h of inoculation, as indicated by the presence of virus-like particles (VLP) in the nuclei. VLP were present in two different arrangements: rod-like structures that appeared in cross-section as paracrystalline arrays of hexagonal-shaped profiles measuring 12 ± 2 nm in diameter and uniformly electron-dense hexagonal-shaped particles measuring , 22,28 nm in diameter. Nuclei containing paracrystalline arrays were most prevalent early in the infection cycle, while cells containing VLP increased and then declined toward the end of the cycle. The proportion of nuclei containing both paracrystalline arrays and VLP remained relatively constant. This pattern suggests that rod-like paracrystalline arrays fragmented to produce icosahedral VLP. C. cf. wighamii nuclear inclusion virus (CwNIV) is characterized by a high burst size (averaged 26,400 viruses per infected cell) and fast generation time that could have ecological implications on C. cf. wighamii population control. [source] MOVEMENT MODALITIES AND RESPONSES TO ENVIRONMENTAL CHANGES OF THE MUDFLAT DIATOM CYLINDROTHECA CLOSTERIUM (BACILLARIOPHYCEAE),JOURNAL OF PHYCOLOGY, Issue 2 2006Melba D. Apoya-Horton Cylindrotheca closterium (Ehrenberg) Reiman et Lewin is a raphid diatom widely distributed in mudflat assemblages. Video microscopy showed various movement modalities defined as smooth and corkscrew gliding, pirouette, pivot, rock and roll, rollover, and simultaneous pirouette and gliding. Z -axis projection analysis of images revealed a unique gliding motif with corkscrew motions, which may have important ecological implications for C. closterium movement in muds. The general response to salinity alteration was a decrease in gliding movements with a concomitant increase in other modalities listed above. Short-term responses to salinity change include dramatic alteration in modalities in hypo-saline conditions and cessation of motility in extreme hyper-saline environments. Modality changes were rapid and occurred within 5 s in response to hyper-saline conditions. Hypo- or hyper-saline conditions resulted in decreased gliding speed in standard media. Five- and 15-day acclimation to salinity changes resulted in a progressive reduction in gliding movement, increased non-gliding modalities and increased cell aggregation. Aggregation in hypo-saline conditions was accompanied by a large increase in the polymer extracted by hot bicarbonate- and ethylenediamine tetraaceticacid- fractions of extracellular polymeric substance (EPS), the polymers of which have been implicated in cell attachment/motility phenomena. The monosaccharide profiles of these fractions were altered in response to hypo-saline conditions. In general, monosaccharide profiles showed increased diversity upon cessation of motility and aggregation of cultures. The movement responses of C. closterium in response to environmental changes, accompanied by modifications in EPS, may form part of an adaptive strategy to survive in mudflats and could be useful as bioindicators of environmental changes. [source] Patterns, sources and ecological implications of clonal diversity in apomictic Ranunculus carpaticola (Ranunculus auricomus complex, Ranunculaceae)MOLECULAR ECOLOGY, Issue 4 2006O. PAUN Abstract Sources and implications of genetic diversity in agamic complexes are still under debate. Population studies (amplified fragment length polymorphisms, microsatellites) and karyological methods (Feulgen DNA image densitometry and flow cytometry) were employed for characterization of genetic diversity and ploidy levels of 10 populations of Ranunculus carpaticola in central Slovakia. Whereas two diploid populations showed high levels of genetic diversity, as expected for sexual reproduction, eight populations are hexaploid and harbour lower degrees of genotypic variation, but maintain high levels of heterozygosity at many loci, as is typical for apomicts. Polyploid populations consist either of a single AFLP genotype or of one dominant and a few deviating genotypes. genotype/genodive and character incompatibility analyses suggest that genotypic variation within apomictic populations is caused by mutations, but in one population probably also by recombination. This local facultative sexuality may have a great impact on regional genotypic diversity. Two microsatellite loci discriminated genotypes separated by the accumulation of few mutations (,clone mates') within each AFLP clone. Genetic diversity is partitioned mainly among apomictic populations and is not geographically structured, which may be due to facultative sexuality and/or multiple colonizations of sites by different clones. Habitat differentiation and a tendency to inhabit artificial meadows is more pronounced in apomictic than in sexual populations. We hypothesize that maintenance of genetic diversity and superior colonizing abilities of apomicts in temporally and spatially heterogeneous environments are important for their distributional success. [source] Spatial differences in acquisition of soil phosphate between two arbuscular mycorrhizal fungi in symbiosis with Medicago truncatulaNEW PHYTOLOGIST, Issue 2 2000F. A. SMITH Responses of Medicago truncatula to colonization by two arbuscular mycorrhizal fungi, Scutellospora calospora isolate WUM 12(2) and Glomus caledonium isolate RIS 42, were compared in the light of previous findings that the former fungus can be ineffective as a beneficial microsymbiont with some host plants. The plants were grown individually in two-compartment systems in which a lateral side arm containing soil labelled with 33P was separated from the main soil compartment by a nylon mesh that prevented penetration by roots but not fungal hyphae. Fungal inoculum was applied as a root,soil mixture in a band opposite the side arm. Nonmycorrhizal controls were set up similarly, without inoculum. There were harvests at 28, 35, 42 and 49 d. Both sets of mycorrhizal plants grew better than nonmycorrhizal plants and initially had higher concentrations of P in shoots and roots. Plants grown with S. calospora grew better than plants grown with G. caledonium, and this was associated with somewhat greater fungal colonization in terms of intraradical hyphae and numbers of arbuscules. Scutellospora calospora formed denser hyphae at root surfaces than G. caledonium. By 28 d there were extensive hyphae of both fungi in the side arms, and after 35 d S. calospora produced denser hyphae there than G. caledonium. Nevertheless, there was very little transfer of 33P via S. calospora to the plant at 28 d, and thereafter its transfer increased at a rate only c. 33% of that via G. caledonium. The results showed that plants colonized by S. calospora preferentially obtained P from sites in the main soil chamber relatively close to the roots, compared with plants colonized by G. caledonium. Hence formation of a highly beneficial arbuscular mycorrhizal symbiosis does not necessarily depend on development of hyphae at a distance from the roots or on large-scale translocation of P from distant sites. The results are discussed in relation to previous studies with compartmented systems that have involved the same fungi. Possible causes of the variable effects of S. calospora in symbiosis with different host plants are briefly assessed. Differences in spatial abilities of individual arbuscular mycorrhizal fungi to acquire P might have strong ecological implications for plant growth in soils low in P. [source] Factors related to the inter-annual variation in plants' pollination generalization levels within a communityOIKOS, Issue 5 2010Amparo Lázaro The number of pollinators of a plant species is considered a measure of its ecological generalization and may have important evolutionary and ecological implications. Many pollination studies report inter-annual fluctuations in the composition of pollinators to particular species. However, the factors causing such variation are still poorly understood. Here we investigate how flowering duration and plant and pollinator assemblages influenced the inter-annual changes in the functional generalization level of the 20 most common plant species of a semi-natural meadow in southern Norway. We also studied the extent to which changes in generalization levels were controlled by flower-shape and flowering time. Large inter-annual changes in generalization levels were common and there was no relationship between the generalization level one year and the following. Generalization level of particular plant species increased with flowering duration, sampling effort, and the abundance of managed honeybees in the community. Generalization level decreased with the flowering synchrony between the focal plant species and the rest of the plant community and with the focal species' own abundance, which we attribute to inter-specific competition for pollinator attraction and foraging decisions made by pollinators. Plants with different flower-shapes and flowering times did not differ in the extent of inter-annual variation in generalization levels. Most studies do not consider the effect of the plant community on the generalization level of particular plant species. We show here that both pollinator and plant assemblages can affect the inter-annual variation in generalization levels of plant species. Studies like ours will help to understand how pollination interactions are structured at the community level, and the ecological and evolutionary consequences that these inter-annual changes in generalization levels may have. [source] Orchid mycorrhiza: implications of a mycophagous life styleOIKOS, Issue 3 2009Hanne N. Rasmussen Orchid mycorrhiza probably affects about 25,000 plant species and thus roughly one tenth of all higher plants. Histologically, this symbiosis resembles other kinds of endomycorrhiza, the fungal hyphae growing within living plant cells. Considerable evidence, however, suggests that it is not a two-way exchange relationship and thus not potentially mutualistic, such as the wide-spread endomycorrhiza between plants and Glomalean fungi, known as arbuscular mycorrhiza. During the achlorophyllous seedling stage orchids are obligately dependent on the fungi; some species remain so through life, while others establish photosynthesis but to varying degrees remain facultatively dependent of /responsive to fungal infection as adults. None of the fungi involved are so far known to depend on the symbiosis with orchids. Transfer of organic carbon compounds from hyphae to the orchid has been demonstrated repeatedly, but it is not clear to what extent this takes place during a biotrophic phase while the intracellular hyphae remain intact, or during the subsequent extensive degradation of the hyphal coils. The advantage of viewing orchid mycorrhiza basically as a unilateral mycophagous relationship, in spite of hypothetical beneficial spin-offs to the mycobiont, is that it provides a conceptual framework similar to that of other parasitic or fungivore relationships; mechanisms known in such relationships could be searched for in future studies of the orchid,fungus symbiosis. These could include mechanisms for recognition, attraction and selection of fungi, physiological regulation of internal hyphal growth, breakdown, and material transfer, nutritional consequences of the plant's preference(s) and trophic changes, fungal avoidance mechanisms, and consequences at population and ecosystem levels. A whole range of possible life strategies becomes apparent that could support divergent evolution and lead to the proliferation of species that has indeed occurred in the orchid family. We outline some of the possible physiological mechanisms and ecological implications of this approach. [source] Mesophyll conductance to CO2: current knowledge and future prospectsPLANT CELL & ENVIRONMENT, Issue 5 2008JAUME FLEXAS ABSTRACT During photosynthesis, CO2 moves from the atmosphere (Ca) surrounding the leaf to the sub-stomatal internal cavities (Ci) through stomata, and from there to the site of carboxylation inside the chloroplast stroma (Cc) through the leaf mesophyll. The latter CO2 diffusion component is called mesophyll conductance (gm), and can be divided in at least three components, that is, conductance through intercellular air spaces (gias), through cell wall (gw) and through the liquid phase inside cells (gliq). A large body of evidence has accumulated in the past two decades indicating that gm is sufficiently small as to significantly decrease Cc relative to Ci, therefore limiting photosynthesis. Moreover, gm is not constant, and it changes among species and in response to environmental factors. In addition, there is now evidence that gliq and, in some cases, gw, are the main determinants of gm. Mesophyll conductance is very dynamic, changing in response to environmental variables as rapid or even faster than stomatal conductance (i.e. within seconds to minutes). A revision of current knowledge on gm is presented. Firstly, a historical perspective is given, highlighting the founding works and methods, followed by a re-examination of the range of variation of gm among plant species and functional groups, and a revision of the responses of gm to different external (biotic and abiotic) and internal (developmental, structural and metabolic) factors. The possible physiological bases for gm, including aquaporins and carbonic anhydrases, are discussed. Possible ecological implications for variable gm are indicated, and the errors induced by neglecting gm when interpreting photosynthesis and carbon isotope discrimination models are highlighted. Finally, a series of research priorities for the near future are proposed. [source] Lolium multiflorum density responses under ozone and herbicide stressAUSTRAL ECOLOGY, Issue 8 2009M. ALEJANDRA MARTÍNEZ-GHERSA Abstract Adaptations to overcrowding of individual plants result in density dependant control of growth and development. There is little information on how anthropogenic stresses modify these responses. We investigated whether combinations of diclofop-methyl herbicide and tropospheric ozone alter the pattern of expected growth compensation with density changes resulting from intraspecific competition in Lolium multiforum Lam (Poacea) plants. Individual plant vegetative parameters and total seed production were assessed for plants growing under various densities and different herbicide rates and ozone treatments. The stressors differently changed the frequency distribution for average individual plant weight resulting from increasing densities. Only herbicide affected seedling mortality. Plants were able to compensate during grain filling maintaining similar seed production , density relationships in all treatments. Our findings contribute to the understanding of the impact of stress factors on the demographic changes in plant populations. Important ecological implications arise: (i) contrasting responses to ozone and herbicide, alone and in combination of individual plants resulted in different biomass , density relationships; (ii) stress effects on plant populations could not be predicted from individual responses; and (iii) changes in competitive outcome by single or combined stress factors may alter the expected genotype frequency in a crowded population with few dominant individuals. [source] Evolutionary and ecological implications of genome size in the North American endemic sagebrushes and allies (Artemisia, Asteraceae)BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2008SÒNIA GARCIA The genome size of 51 populations of 20 species of the North American endemic sagebrushes (subgenus Tridentatae), related species, and some hybrid taxa were assessed by flow cytometry, and were analysed in a phylogenetic framework. Results were similar for most Tridentatae species, with the exception of three taxonomically conflictive species: Artemisia bigelovii Gray, Artemisia pygmaea Gray, and Artemisia rigida Gray. Genome size homogeneity (together with the high morphological, chemical, and karyological affinities, as well as low DNA sequence divergence) could support a recent diversification process in this geographically restricted group, thought to be built upon a reticulate evolutionary framework. The Tridentatae and the other North American endemic Artemisia show a significantly higher genome size compared with the other subgenera. Our comparative analyses including genome size results, together with different kinds of ecological and morphological traits, suggest an evolutionary change in lifestyle strategy linked to genome expansion, in which junk or selfish DNA accumulation might be involved. Conversely, weed or invasive behaviour in Artemisia is coupled with lower genome sizes. Data for both homoploid and polyploid hybrids were also assessed. Genome sizes are close to the expected mean of parental species for homoploid hybrids, but are lower than expected in the allopolyploids, a phenomenon previously documented to be related with polyploidy. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 631,649. [source] | |||||||||||||||||||||||||