Although reproductive assurance has been suggested to be one of the most important factors shaping the differential distributional patterns between sexuals and asexuals (geographic parthenogenesis), it has only rarely been studied in natural populations of vascular plants with autonomous apomixis. Moreover, there are almost no data concerning the putative relationship between the level of apomictic versus sexual plant reproduction on one hand, and reproductive assurance on the other.
We assessed the level of sexual versus apomictic reproduction in diploid and triploid plants of Hieracium alpinum across its distributional range using flow cytometric analyses of seeds, and compared the level of potential and realized seed set, i.e. reproductive assurance, between the two cytotypes under field and greenhouse conditions.
Flow cytometric screening of embryos and endosperms of more than 4,100 seeds showed that diploids produced solely diploid progeny sexually, while triploids produced triploid progeny by obligate apomixis. Potential fruit set was much the same in diploids and triploids from the field and the greenhouse experiment. While in the pollination‐limited environment in the greenhouse apomictic triploids had considerably higher realized fruit set than sexual diploids, there was no significant difference between cytotypes under natural conditions. In addition, sexuals varied to a significantly larger extent in realized fruit set than asexuals under both natural and greenhouse conditions.
Our results indicate that triploid plants reproduce by obligate apomixis, assuring more stable and predictable fruit reproduction when compared to sexual diploids. This advantage could provide apomictic triploids with a superior colonisation ability, mirrored in a strong geographic parthenogenesis pattern observed in this species.
Responses of Vegetation Stages with Woody Dominants to Stress and Disturbance During Succession on Abandoned Tailings in Cultural LandscapeStudies of ecological succession on tailing containments (abandoned sedimentation basins with waste deposited by a factory producing sulphuric acid from pyrite ore) near the village of Chvaletice (Eastern Bohemia, Czech Republic) were carried out since 1973 with increased intensity and complexity between 1986 and 2002 (Kovář 2004). Vegetation cover in its relationships to various factors has been periodically monitored up to now. The abandoned ore-washery deposit is characterized by relative strong toxicity of the sediment material (high heavy metal content) and fluctuations of the microsite conditions up to extreme values (pH, salinity, surface temperatures). Species richness and the courses of some ecological processes are influenced both by availability of plant diaspores (regional species pool) determined with the presence of adequate dispersal mechanisms (anemochory, zoochory) and by the seasonal moderation of environmental variables excluding stress non-tolerant species at extreme epizodes and enabling survival of resistant species during the competition. Long lasting existence of patches without any vegetation together with herbaceous types of stands and woody successional stages create mosaics on the surface plateau. The oldest tree stands (in average 20 - 30 years old) are predominantly formed byPopulus tremulaandBetula pendula, with minor admixture ofSalixsp. div. (mainlyS. caprea),Pinus sylvestris,Quercus roburorCerassus avium, rarelySarothamnus scoparius.The abundance ratio of two main dominants, aspen and birch, was changed for the benefit of the first one after the summer fire in extremely hot days. The effect of clonality on aspen regeneration and regrowth immediately after the fire disturbance was profitably manifested and it apparently facilitates the present state with aspen prevailing in the most forested tailing places at present, seventeen years after the fire. This fact supports the importance of clonal plant species role during primary succession.
This article examines the consequences of a fire (August 1994) which burned the vegetated surface of abandoned tailings containment in mosaic pattern, in Chvaletice (Eastern River Elbe basin, Czech Republic). Vegetation succession with adjacent processes (such as leaf litter decomposition) was then monitored in comparisons on burned and unburned plots. The influence of the introduced plant organic matter by mulching on the biological soil crust was also investigated. Apart from the naturally burned plots, some plots were also experimentally burned. The soil moisture and surface temperatures in different temporal distances from the fire experiment were measured. There were no significant differences in decomposition rate between the plots that were affected and/or unaffected by fire. The daily temperatures of the burned soil surface increased after the fire, while its night temperatures decreased. The moisture content of the soil surface was reduced after the fire. Addition of dry local aboveground plant biomass on the substrate surface suggests that substrate roughness provides retention to seeds transported by wind, and protects the rhizosphere against extreme heat, drought and salt incrustation. Furthermore, it positively modifies the hydrological regime of microsites and stimulates the creation of a humus soil layer and enrichment of the substrate by nutrients. Finally, it facilitates colonisation by plant seedlings from seeds transported by anemochorous or zoochorous mechanisms.
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