Price T, Sol D (2008) Genetics of Colonizing Species. American Naturalist 172: S1-S3.
De Las Heras J., Moya D., López-Serrano F.R., Eugenio M., Espelta J.M. (2008) Aleppo pine regeneration after fire along an aridity gradient. WIT Transactions on Ecology and the Environment. 119: 289-295.EnllaçDoi: 10.2495/FIVA080291
In the Mediterranean Basin, the number of large-scale fires and, consequently, the area of regenerated forests after a fire have been increasing over the last few decades. Mediterranean pine tree stand regeneration shows differences in growth and reproductive characteristics depending on site quality. Aleppo pine (Pinus halepensis Mill.) is an important obligate seeder species occupying a large surface in this area. In order to study growth and reproductive characteristics depending on different climatic conditions, six sites with similar characteristics (edaphic, exposure, slope) burned in the summer of 1994 were selected along a climate gradient. Different precipitation values determined three different ombroclimates: dry-subhumid, dry and semi-arid. Ten years after the fires, data on growth and cone production were collected from these areas in order to study the pattern of growth and reproduction and the influence of site quality (climate) on them. Results showed significantly higher values for growth and several cone characteristics; furthermore, they were positively related to site quality. Viability and seed germination percentages were higher in sites located in dry-subhumid areas. Serotiny was highest in dry locations (southern sites), and lower percentages were found in low tree density sites. The number of reproductive trees was higher northwards and the reproductive phase was reached in younger stands with lower tree density. In conclusion, results showed a geographical gradient based upon growth and reproductive characteristics, decreasing southwards in contrast to serotiny, which increases in southern sites. Density was found to be a significant factor influencing overall pine stand development.
Domene X., Alcañiz J.M., Andrés P. (2008) Comparison of solid-phase and eluate assays to gauge the ecotoxicological risk of organic wastes on soil organisms. Environmental Pollution. 151: 549-558.EnllaçDoi: 10.1016/j.envpol.2007.04.007
Development of methodologies to assess the safety of reusing polluted organic wastes in soil is a priority in Europe. In this study, and coupled with chemical analysis, seven organic wastes were subjected to different aquatic and soil bioassays. Tests were carried out with solid-phase waste and three different waste eluates (water, methanol, and dichloromethane). Solid-phase assays were indicated as the most suitable for waste testing not only in terms of relevance for real situations, but also because toxicity in eluates was generally not representative of the chronic effects in solid-phase. No general correlations were found between toxicity and waste pollutant burden, neither in solid-phase nor in eluate assays, showing the inability of chemical methods to predict the ecotoxicological risks of wastes. On the contrary, several physicochemical parameters reflecting the degree of low organic matter stability in wastes were the main contributors to the acute toxicity seen in collembolans and daphnids. © 2007 Elsevier Ltd. All rights reserved.
Domene X., Ramírez W., Mattana S., Alcañiz J.M., Andrés P. (2008) Ecological risk assessment of organic waste amendments using the species sensitivity distribution from a soil organisms test battery. Environmental Pollution. 155: 227-236.EnllaçDoi: 10.1016/j.envpol.2007.12.001
Safe amendment rates (the predicted no-effect concentration or PNEC) of seven organic wastes were estimated from the species sensitivity distribution of a battery of soil biota tests and compared with different realistic amendment scenarios (different predicted environmental concentrations or PEC). None of the wastes was expected to exert noxious effects on soil biota if applied according either to the usual maximum amendment rates in Europe or phosphorus demands of crops (below 2 tonnes DM ha-1). However, some of the wastes might be problematic if applied according to nitrogen demands of crops (above 2 tonnes DM ha-1). Ammonium content and organic matter stability of the studied wastes are the most influential determinants of the maximum amendment rates derived in this study, but not pollutant burden. This finding indicates the need to stabilize wastes prior to their reuse in soils in order to avoid short-term impacts on soil communities. © 2007 Elsevier Ltd. All rights reserved.
Domènech R., Vilà M. (2008) Response of the invader Cortaderia selloana and two coexisting natives to competition and water stress. Biological Invasions. 10: 903-912.EnllaçDoi: 10.1007/s10530-008-9243-0
Alien species' resistance and adjustment to water stress and plant competition might largely determine the success of invasions in Mediterranean ecosystems because water availability is often limiting biomass production. Two outdoor pot experiments were conducted to test the hypotheses that at the recruitment stage the invader perennial tussock grass Cortaderia selloana is a superior competitor, and that it is more resistant to water stress than the two coexisting native species of the same functional group, Festuca arundinacea and Brachypodium phoenicoides. C. selloana reduced aboveground biomass of target native species, but not more than target native species on each other. Moreover, C. selloana did not resist interspecific competition more than target native species. Under control conditions, C. selloana did not have larger specific leaf area (SLA) and root-shoot ratio (R/S) ratio than target native species, contradicting the general statement that these traits are associated to invasiveness. F. arundinacea was the species which performed best but also the one most affected by water stress. Both C. selloana and B. phoenicoides performed in a similar way under water stress conditions. However, the alien species' capacity to adjust to water stress, indicated by the increase in the root-shoot ratio under moderate and severe water stress, was slightly better than that of B. phoenicoides. Overall, at early recruitment stages, C. selloana is not a better competitor than the coexisting native species. However, it seems to be more resistant to water stress because as water becomes scarce C. selloana maximizes water uptake and minimizes water losses more than the native species. © 2008 Springer Science+Business Media B.V.
Domènech R., Vilà M. (2008) Cortaderia selloana seed germination under different ecological conditions. Acta Oecologica. 33: 93-96.EnllaçDoi: 10.1016/j.actao.2007.09.004
Biological invasions are causing the extinction of native species and modifying ecosystem functions. Invasion success depends, among other factors, on the biological attributes of the invaders and the abiotic characteristics of the recipient community. Cortaderia selloana is a gynodioecious perennial grass native to South America which is considered invasive worldwide. It is known that seedlings of this species tolerate a wide range of environmental conditions. However, the abiotic factors that may favour its seed germination have not been studied in much detail. For this reason, we conducted an array of germination tests with different degrees of shading, soil textures and water availability. Although C. selloana usually grows in disturbed sites where light is highly available, we found that seed germination was higher under shaded conditions than under 100% light. Seed germination was higher in sandy soil textures and decreased in soils which contained increased levels of clay. Mature C. selloana plants have been reported to tolerate water stress, yet we found that the shortage of water availability constrained seed germination to approximately 60%. Overall, C. selloana seeds seem to germinate under a wide range of environmental conditions, yet germination rate can be improved under shading, high levels of sand and with high water availability. © 2007.
Dubreuil M., Riba M., Mayol M. (2008) Genetic structure and diversity in Ramonda myconi (Gesneriaceae): Effects of historical climate change on a preglacial relict species. American Journal of Botany. 95: 577-587.EnllaçDoi: 10.3732/ajb.2007320
The importance of the Mediterranean Basin as a long-term reservoir of biological diversity has been widely recognized, although much less effort has been devoted to understanding processes that allow species to persist in this area. Ramonda myconi (Gesneriaceae) is a Tertiary relict plant species restricted to the NE Iberian Peninsula. We used RAPD and chloroplast markers to assess the patterns of genetic structure in eight mountain regions covering almost the full species range, to identify the main historical processes that have shaped its current distribution and to infer the number and location of putative glacial refugia. While no cpDNA variation was detected, the species had relatively high levels of RAPD variation. Maximum levels of diversity were found within populations (71%), but there was also a significant differentiation between geographical regions (20%) and among populations within regions (9%). A spatial AMOVA identified three main groups of populations, corresponding to previously recognized centers of endemism and species richness. In addition, we found a marked geographical pattern of decreasing genetic diversity and increasing population differentiation from west to east. Our results support a complex phylogeographic scenario in the Iberian Peninsula of "refugia-within-refugia" and suggest that the higher diversity observed in western regions might be associated with prolonged and more stable climatic conditions in this area during the Quaternary.
Dubreuil M., Sebastiani F., Mayol M., González-Martínez S.C., Riba M., Vendramin G.G. (2008) Isolation and characterization of polymorphic nuclear microsatellite loci in Taxus baccata L.. Conservation Genetics. 9: 1665-1668.EnllaçDoi: 10.1007/s10592-008-9515-3
Seven polymorphic nuclear microsatellite markers for Taxus baccata L. (English yew) were developed using an enriched-library method. An additional polymorphic SSR was obtained by testing eight primer pairs from the congeneric species Taxus sumatrana. Mendelian inheritance for the seven Taxus baccata SSRs was proved by genotyping 17 individuals and 124 megagametophytes (conifer seed haploid tissue). A total of 96 individuals from 5 different populations (10-26 samples per population) were used to estimate genetic diversity parameters. High levels of genetic diversity, with values ranging from 0.533 to 0.929 (6-28 alleles per SSR) were found. No linkage disequilibrium between pairs of loci was detected. All loci but one showed significant departures from Hardy-Weinberg equilibrium. Excess of homozygosity was probably due to high inbreeding in English yew populations, an outcome of low effective population size and/or fragmented distribution. Highly polymorphic SSRs will be used to conduct population genetic studies at different geographical scales and to monitor gene flow. © 2008 Springer Science+Business Media B.V.
Elisabeth Z.P., Paco S., Vibeke L., Philippe S., Irénée S., Adama N. (2008) Importance of seed-borne fungi of sorghum and pearl millet in Burkina Faso and their control using plant extracts. Pakistan Journal of Biological Sciences. 11: 321-331.EnllaçDoi: 10.3923/pjbs.2008.321.331
Seed-borne fungi of sorghum and pearl millet in Burkina Faso were surveyed. A total of 188 seed samples from various locations, collected in 1989 (42) and 2002 (146), were tested, using the blotter, dry inspection and washing methods. Infection experiments were carried out with the major fungi recorded on each crop by the blotter test. Six essential oils of plants were investigated for their inhibitory activity against eight pathogenic fungi. Thirty four and 27 fungal species were found m seed samples of sorghum and pearl millet, respectively. Phoma sp. and Fusarium moniliforme infected 95 to 100% of the seed samples of both sorghum and pearl millet. Sphacelotheca sorghi and Tolyposporium ehrenbergii were encountered in respectively, 75 and 33% of seed samples of sorghum. T. penicillariae, Sclerospora graminicola and Clavicepsfusiformis were present in 88, 41 and 32% of seed samples of pearl millet, respectively. Seeds inoculated with Acremonium strictum, Curvularia oryzae, F. equiseti, F. moniliforme and F. subglutinans and sown in sterilized soil, showed considerable mortality of the seedlings. Three essential oils inhibited in vitro the mycelial growth of all the fungi used by 85 to 100% and reduced significantly sorghum and pearl millet seed infection rates of Phoma sp., Fusarium sp., Curvularia sp., Colletotrichum graminicola and Exserohilum sp. Presence of many pathogenic fungi in considerable number of seed samples indicates the need of field surveys for these and other pathogens. Development of plant extracts for the control of seed-borne pathogens and public awareness on seed-borne diseases management measures for maintaining quality seed should be increased. © 2008 Asian Network for Scientific Information.
Espelta J.M., Cortés P., Molowny-Horas R., Sánchez-Humanes B., Retana J. (2008) Masting mediated by summer drought reduces acorn predation in mediterranean oak forests. Ecology. 89: 805-817.EnllaçDoi: 10.1890/07-0217.1
Temporally variable production of seed crops by perennial plants (masting) has been hypothesized to be a valuable mechanism in the reduction of seed predation by satiating and starving seed consumers. To achieve these benefits, coexisting species subjected to the same predator would benefit from a similar pattern of seeding fluctuation over time that could lead to a reduction in predation at the within-species level. We tested for the existence of an environmental factor enforcing synchrony in acorn production in two sympatric Mediterranean oaks (Quercus ilex and Q. humilis) and the consequences on within-species and between-species acorn predation, by monitoring 15 mixed forests (450 trees) over seven years. Acorn production in Q. ilex and Q. humilis was highly variable among years, with high population variability (CVp) values. The two species exhibited a very different pattern across years in their initial acorn crop size (sum of aborted, depredated, and sound acorns). Nevertheless, interannual differences in summer water stress modified the likelihood of abortion during acorn ripening and enforced within- and, particularly, between-species synchrony and population variability in acorn production. The increase in CVp from initial to mature acorn crop (after summer) accounted for 33% in Q. ilex, 59% in Q. humilis, and 60% in the two species together. Mean yearly acorn pre-dispersal predation by invertebrates was considerably higher in Q. humilis than in Q. ilex. Satiation and starvation of predators was recorded for the two oaks, and this effect was increased by the year-to-year variability in the size of the acorn crop of the two species combined. Moreover, at a longer time scale (over seven years), we observed a significant reduction in the mean proportion of acorns depredated for each oak and the variability in both species' acorn production combined. Therefore, our results demonstrate that similar patterns of seeding fluctuation over time in coexisting species mediated by an environmental cue (summer drought) may contribute to the reduction of the impact of seed predation at a within-species level. Future research should be aimed at addressing whether this process could be a factor assisting in the coexistence of Q. ilex and Q. humilis. © 2008 by the Ecological Society of America.
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