Research into Plant Invasions in a Crossroads Region: History and Focus

The Czech Republic is a central European country whose geographical location, natural conditions, history of human settlement, and present land-use management make it relatively prone to plant invasions, hence it represents a convenient model for their study. Research in plant invasions, which date to the late 19th century, is reviewed in the present paper. A long-term floristic tradition allowed for the accumulation of a large body of floristic data on alien plants. During the 1960s–1970s, the main research focus was on their distribution. In this period, attempts were also made to predict potential invasiveness of weeds of arable land. The success rate of this prediction was about 39%. Considerable effort was put into a detailed classification of human-accompanying plants and the terminology associated with the issue. There is a high level of taxonomic research conducted in the country, and the new Flora of the Czech Republic treats the immigration status of taxa with reasonable care and detail. A complete, serious catalogue of the alien plants of the country has been published recently: there are currently 1378 alien plants (33.4% of the total flora). The core of present research in plant invasions is in ecological, biological, and biogeographical studies, focussed on (i) the history of invasion of particular species since their introduction, (ii) the role and importance of alien species in vegetation, including their participation in succession, and (iii) the major invasive species of the Czech flora and comparison of congeners. Reynoutria spp., Heracleum mantegazzianum, Oenothera spp., Pinus strobus, and Bidens frondosa are among the taxa most intensively studied in recent time. A complete list of 69 invasive plants in the Czech flora introduced after the year 1500 [following the definition of Richardson et al. (2000a) Diversity and Distributions 6: 93–107] is given. The available legal instruments relevant to the issue are reviewed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fed-batch cultivation of baker's yeast followed by nitrogen or carbon starvation: effects on fermentative capacity and content of trehalose and glycogen

An industrial strain of Saccharomyces cerevisiae (DGI 342) was cultivated in fed-batch cultivations at a specific growth rate of 0.2 h(-1). The yeast was then exposed to carbon or nitrogen starvation for up to 8 h, to study the effect of starvation on fermentative capacity and content of protein, trehalose and glycogen. Nitrogen starvation triggered the accumulation of trehalose and glycogen. After 8 h of starvation, the content of trehalose and glycogen was increased 4-fold and 2-fold, respectively. Carbon starvation resulted in a partial conversion of glycogen into trehalose. The trehalose content increased from 45 to 64 mg (g dry-weight)(-1), whereas the glycogen content in the same period was reduced from 55 to 5 mg (g dry-weight)(-1). Glycogen was consumed faster than trehalose during storage of the starved yeast for 1 month. Nitrogen starvation resulted in a decrease in the protein content of the yeast cells, and the fermentative capacity per gram dry-weight decreased by 40%. The protein content in the carbon-starved yeast increased as a result of starvation due to the fact that the content of glycogen was reduced. The fermentative capacity per gram dry-weight was, however, unaltered.     

Mutagenesis of cellulase EGZ for studying the general protein secretory pathway in Erwinia chrysanthemi

Extracellular secretion of endoglucanase Z (EGZ) from Erwinia chrysanthemi is mediated by the so-called Out general secretion pathway and, presumably, involves recognition of EGZ-carried structural information by one or more of the Out proteins. Investigating the relationships between structure and secretability of EGZ was the purpose of the present work. EGZ is made of two independent domains, located at the N-and C-proximal sides, separated by a Ser/Thr-rich region, which are responsible for catalysis and cellulose-binding, respectively. The existence of a secretion region (‘targeting signal’) was investigated by studying the secretability of modified EGZ derivatives. These resulted from deletion or peptide insertion and were designed by using the domain organization cited above as a guide. Catalytic and/or cellulose-binding tests showed that all proteins exhibited at least a functional EGZ domain while immunoblot analyses confirmed that neither the insertions nor the deletions led to grossly misfolded proteins. In contrast, all of the proteins lost their secretability in E. chrysanthemi. This suggested that at least two secretion motifs existed, one lying within each functional domain. The role of the Ser/Thr-rich linker region was subsequently tested. Accordingly, two proteins containing a linker region whose length was increased by the addition of 8 and 18 additional residues and one protein lacking the linker region were studied. All three exhibited endoglucanase activity and cellulose-binding ability, confirming the independence of the domains within the context of EGZ/polysaccharide interaction. In contrast, none was secreted by E. chrysanthemi. Collectively, our results with EGZ (i) suggest the occurrence of multiple secretion-related sites either acting sequentially or forming a single three-dimensional secretion signal, (ii) show that secretability is not determined by either one of the two functional domains alone, and (iii) reveal that the linker region plays a role in secretion. We propose that all EGZ derivatives were impaired in the recognition step, the nature of which is discussed.     

Pattern of species dominance and factors affecting community composition in areas deforested due to air pollution

Vegetation of mountain areas affected by SO₂ pollution (Kruné hory Mts., Czech Republic) was analysed using multivariate methods. Communities with prevailing species Calamagrostis villosa, a rhizomatous grass expanding into deforested sites, were sampled by Braun-Blanquet relevé method. Canonical correspondence analysis was used to assess the effect of environmental variables (soil removal, deforestation, and shading). To test the effects of light, moisture, soil acidity and nitrogen, mean sample indicator values were correlated a posteriori with sample axes on ordination scores. Light, soil acidity, moisture, and site history (in terms of past deforestation and soil removal applied in reclamation procedures) were found to be the main factors responsible for the community composition. Nitrogen level had not a significant effect on the community composition. When analyzing the whole data set, i.e. including also remnants of natural spruce forests, light was the factor affecting at most the composition of communities. Within the bare spot vegetation, if treated separately, the highest variation was found along the soil acidity/moisture gradient. The effect of soil removal was only obvious at early successional stages. Species diversity increased with moisture and decreased with soil acidity. Species exhibiting S- and/or R-strategy are successful on extremely acid soils whereas forbs present in bare spots appear to be supported by disturbances.     

Organic and inorganic nitrogen uptake in lichens

In order to learn more about nitrogen (N) acquisition in lichens, and to see whether different lichens differ in their affinity to various N sources, N uptake was measured in 14 various lichen associations (species). These species represented various morphologies (fruticose or foliose), contrasting microhabitat preferences (epiphytic or terricolous), and had green algal, cyanobacterial or both forms of photobionts. N was supplied under non-limiting conditions as an amino acid mixture, ammonium, or nitrate, using ¹⁵N to quantify uptake. Carbonyl cyanide m-chlorophenylhydrazone (CCCP) was used to separate active and passive uptake. Thallus N, amino acids, soluble polyol concentrations, and the biont-specific markers chlorophyll a and ergosterol were quantified, aiming to test if these metabolites or markers were correlated with N uptake capacity. Ammonium uptake was significantly greater and to a higher extent passive, relative to the other two N sources. Nitrate uptake differed among lichen photobiont groups, cyanobacterial lichens having a lower uptake rate. All lichens had the capacity to assimilate amino acids, in many species at rates equal to nitrate uptake or even higher, suggesting that organic N compounds could potentially have an important role in the N nutrition of these organisms. There were no clear correlations between N uptake rates and any of the measured metabolites or markers. The relative uptake rates of ammonium, nitrate and amino acids were not related to morphology or microhabitat.Abbreviations CCCP Carbonyl cyanide m-chlorophenylhydrazone - Chl Chlorophyll - N Nitrogen