Fern

Abstract: The homosporous pteridophytes have been largely uninvestigated by electrophoresis, despite the fact that they offer many exciting research possibilities (Soltis et al., 1980). The paucity of electrophoretic studies of ferns and fern allies may be due in large part to the high concentrations of condensed tannins that many species contain (Cooper-Driver, 1976 and pers. comm.). These compounds render enzymes inactive by binding with them following cellular disruption, thereby frustrating researchers who have attempted electrophoretic analysis utilizing standard methods of sample preparation. The method of sample preparation developed by Kelley and Adams (1977a, b) in their analysis of enzyme variation in Juniperus was an important procedural breakthrough in overcoming the difficulties that result from the liberation of large amounts of phenolic compounds during tissue preparation. Recently, a simplified version of that method was applied by Soltis et al. (1980) to fern leaf tissue, facilitating rapid preparation of active enzyme samples and thereby making electrophoretic analyses of large numbers of individuals more feasible. In an attempt to improve methods of analysis of fern enzymes in starch gel electrophoresis, we have experimented with modifications of the method of sample preparation outlined by Soltis et al. (1980). We also have examined several different methods of sample preparation such as those of Gottlieb (1981a), Mitton et al. (1979), and Werth et al. (1982), and have evaluated the relative merits of each with fern tissue. Finally, during the course of our electrophoretic investigations of ferns we found that standard gel and electrode buffers and staining schedules, such as those of Brewer (1970) and Shaw and Prasad (1970), often provided unsatisfactory results when applied to ferns. We have determined gel and electrode buffers, as well as staining schedules, that provide clear starch gel enzyme banding for 22 enzyme systems in ferns. Requests for advice resulting from the recent surge of interest in fern enzyme electrophoresis have prompted us to compile our procedural data so that other researchers can take advantage of our experimentation. We hope that these data will stimulate more extensive electrophoretic investigation of pteridophytes and other electrophoretically difficult taxa. Gottlieb (1981b) recently reviewed aspects of enzyme electrophoresis primarily in gymnosperms and angiosperms. His discussion is equally relevant to understanding the potential applications and limitations of electrophoretic evidence in pteridophytes. Since homosporous pteridophytes have high chromosome numbers, it is tempting to invoke polyploidy in interpreting their enzyme band patterns. It is well

Abstract: The rise of angiosperms during the Cretaceous period is often portrayed as coincident with a dramatic drop in the diversity and abundance of many seed-free vascular plant lineages, including ferns. This has led to the widespread belief that ferns, once a principal component of terrestrial ecosystems, succumbed to the ecological predominance of angiosperms and are mostly evolutionary holdovers from the late Palaeozoic/early Mesozoic era. The first appearance of many modern fern genera in the early Tertiary fossil record implies another evolutionary scenario; that is, that the majority of living ferns resulted from a more recent diversification. But a full understanding of trends in fern diversification and evolution using only palaeobotanical evidence is hindered by the poor taxonomic resolution of the fern fossil record in the Cretaceous. Here we report divergence time estimates for ferns and angiosperms based on molecular data, with constraints from a reassessment of the fossil record. We show that polypod ferns (> 80% of living fern species) diversified in the Cretaceous, after angiosperms, suggesting perhaps an ecological opportunistic response to the diversification of angiosperms, as angiosperms came to dominate terrestrial ecosystems.

Abstract: Throughout the history of the classification of extant ferns (monilophytes) and lycophytes, familial and generic concepts have been in great flux. For the organisation of lycophytes and ferns in herbaria, books, checklists, indices and spore banks and on the internet, this poses a problem, and a standardized linear sequence of these plants is therefore in great need. We provide here a linear classification to the extant lycophytes and ferns based on current phylogenetic knowledge; this provides a standardized guide for organisation of fern collections into a more natural sequence. Two new families, Diplaziopsidaceae and Rhachidosoraceae, are here introduced.

Abstract: Physiological traits that contribute to the establishment and spread of invasive plant species could also have impacts on ecosystem processes. The traits prevalent in many invasive plants, such as high specific leaf areas, rapid growth rates, and elevated leaf nutrient concentrations, improve litter quality and should increase rates of decomposition and nutrient cycling. To test for these ecosystem impacts, we measured initial leaf litter properties, decomposition rates, and nutrient dynamics in 11 understory plants from the Hawaiian islands in control and nitrogen + phosphorus fertilized plots. These included five common native species, four of which were ferns, and six aggressive invasive species, including five angiosperms and one fern. We found a 50-fold variation in leaf litter decay rates, with natives decaying at rates of 0.2-2.3 year(-1) and invaders at 1.4-9.3 year(-1). This difference was driven by very low decomposition rates in native fern litter. Fertilization significantly increased the decay rates of leaf litter from two native and two invasive species. Most invasive litter types lost nitrogen and phosphorus more rapidly and in larger quantities than comparable native litter types. All litter types except three native ferns lost nitrogen after 100 days of decomposition, and all litter types except the most recalcitrant native ferns lost >50% of initial phosphorus by the end of the experiment (204-735 days). If invasive understory plants displace native species, nutrient cycling rates could increase dramatically due to rapid decomposition and nutrient release from invasive litter. Such changes are likely to cause a positive feedback to invasion in Hawai'i because many invasive plants thrive on nutrient-rich soils.