Year of publication
- 2012 (5) (remove)
- Festuco-Brometea communities of the Transylvanian Plateau (Romania) – a preliminary overview on syntaxonomy, ecology, and biodiversity (2012)
- The Transylvanian Plateau in Romania is well known to host large areas of a variety of dry grassland types, still traditionally managed by low-intensity mowing or grazing. While this natural heritage is now under threat from changes in agricultural practices, the diversity of Transylvanian dry grasslands is still little understood. There is a lack of both field data sampled with standardised methods and a syntaxonomic treatment with modern statistical methods and supra-regional perspective. Therefore, the European Dry Grassland Group (EDGG) carried out its first international Research Expedition in Transylvania 2009 to study syntaxonomy, vegetation-environment relationships, and biodiversity patterns of these communities. In various locations across Transylvania, we sampled 10-m² vegetation plots (n = 82) and nested-plot series from 0.0001 m² to 100 m² (n = 20), including all vascular plant, bryophyte, and lichen species, as well as structural and soil data. The vegetation classification was carried out with modified TWINSPAN, followed by determination of diagnostic species with phi values and a small-scale re-assignment of relevés with the aim of crispness maximisation. Both TWINSPAN and ordination revealed three major groups of syntaxa, which were matched to three orders from the class of basiphilous dry grasslands, Festuco-Brometea, represented by one alliance each: rocky dry grasslands (Stipo pulcherrimae-Festucetalia pallentis: Seslerion rigidae); xeric grasslands on deep soils (Festucetalia valesiacae: Stipion lessingianae) and meso-xeric grasslands on deep soils (Brachypodietalia pinnati: Cirsio-Brachypodion pinnati). We accepted nine association-level units plus two that potentially merit association status but were only represented by one relevé each. Most of the units could be identified with one or several previously described associations. To support nomenclatural stability, we provide a nomenclatural revision and designate nomenclatural types where previously there were none. Further, we used DCA ordination and analysis of variance to determine the main environmental drivers of floristic differentiation and to determine ecological and structural differences between the vegetation types. The strongest differentiation occurred along the aridity gradient with the dense, particularly diverse stands on more or less level sites on the one hand (Brachypodietalia pinnati) and the more open, less diverse stands on steep south-facing slopes on the other end of the gradient (Stipo pulcherrimae- Festucetalia pallentis, Festucetalia valesiacae). The two xeric orders were then separated along the second DCA axis, with the Stipo pulcherrimae-Festucetalia pallentis inhabiting the stone-rich sites at higher altitudes while the Festucetalia valesiacae occur on soft, deep substrata at lower altitudes. The analysed dry grassland communities have extraordinarily high -diversity at all spatial scales for all plants and for vascular plants, but are relatively poor in bryophytes and lichens. Some formerly mown stands of the Festuco sulcatae-Brachypodietum pinnati (Brachypodietalia pinnati) are even richer in vascular plant species than any other recorded vegetation type worldwide on the spatial scales of 0.1 m² (43) and 10 m² (98); the respective relevés are documented here for the first time. Also, the -diversity of the grasslands was unexpectedly high, with a mean z-value of 0.275. Despite its limited extent, the methodological thoroughness of this study allows us to shed new light on the syntaxonomy of dry grasslands in Romania and to raise the awareness that Transylvania still hosts High Nature Value grasslands that are bio - diversity hotspots at a global scale but at the same time are highly endangered through changes in agricultural practices.
- Entorhinal denervation induces homeostatic synaptic scaling of excitatory postsynapses of dentate granule cells in mouse organotypic slice cultures (2012)
- Denervation-induced changes in excitatory synaptic strength were studied following entorhinal deafferentation of hippocampal granule cells in mature (≥3 weeks old) mouse organotypic entorhino-hippocampal slice cultures. Whole-cell patch-clamp recordings revealed an increase in excitatory synaptic strength in response to denervation during the first week after denervation. By the end of the second week synaptic strength had returned to baseline. Because these adaptations occurred in response to the loss of excitatory afferents, they appeared to be in line with a homeostatic adjustment of excitatory synaptic strength. To test whether denervation-induced changes in synaptic strength exploit similar mechanisms as homeostatic synaptic scaling following pharmacological activity blockade, we treated denervated cultures at 2 days post lesion for 2 days with tetrodotoxin. In these cultures, the effects of denervation and activity blockade were not additive, suggesting that similar mechanisms are involved. Finally, we investigated whether entorhinal denervation, which removes afferents from the distal dendrites of granule cells while leaving the associational afferents to the proximal dendrites of granule cells intact, results in a global or a local up-scaling of granule cell synapses. By using computational modeling and local electrical stimulations in Strontium (Sr2+)-containing bath solution, we found evidence for a lamina-specific increase in excitatory synaptic strength in the denervated outer molecular layer at 3–4 days post lesion. Taken together, our data show that entorhinal denervation results in homeostatic functional changes of excitatory postsynapses of denervated dentate granule cells in vitro.
- Functional and structural properties of dentate granule cells with hilar basal dendrites in mouse entorhino-hippocampal slice cultures (2012)
- During postnatal development hippocampal dentate granule cells (GCs) often extend dendrites from the basal pole of their cell bodies into the hilar region. These so-called hilar basal dendrites (hBD) usually regress with maturation. However, hBDs may persist in a subset of mature GCs under certain conditions (both physiological and pathological). The functional role of these hBD-GCs remains not well understood. Here, we have studied hBD-GCs in mature (≥18 days in vitro) mouse entorhino-hippocampal slice cultures under control conditions and have compared their basic functional properties (basic intrinsic and synaptic properties) and structural properties (dendritic arborisation and spine densities) to those of neighboring GCs without hBDs in the same set of cultures. Except for the presence of hBDs, we did not detect major differences between the two GC populations. Furthermore, paired recordings of neighboring GCs with and without hBDs did not reveal evidence for a heavy aberrant GC-to-GC connectivity. Taken together, our data suggest that in control cultures the presence of hBDs on GCs is neither sufficient to predict alterations in the basic functional and structural properties of these GCs nor indicative of a heavy GC-to-GC connectivity between neighboring GCs.
- Biodiversity, syntaxonomy, and management – Editorial to the 7th Dry Grassland Special Feature (with a bibliometrical evaluation of the series) (2012)
- We report on the activities of the European Dry Grassland Group (EDGG) during the last year, namely the 8th European Dry Grassland Meeting in Uman’, Ukraine in June 2011, the 3rd EDGG Research Expedition in Bulgaria in August 2011, the 4th EDGG Research Expedition in Sicily in April 2012, as well as the completed and forthcoming EDGG-coordinated special features in international journals. Then we provide a brief bibliometrical analysis of the Dry Grassland Special Features in Tuexenia since 2005. The 32 contributions of the years 2005–2011 constituted approx. 17% of the overall content of Tuexenia in this period. Including this 7th Dry Grassland Special Feature, sixty-one authors from 12 countries have contributed to these Special Features, guest-edited by yearly changing teams from a total of 16 guest editors. In the years with statistically reliable data, contributions in the Dry Grassland Special Features have been cited approximately four times as much as regular Tuexenia contributions. It is likely that this fact together with the internationality of the Special Features has contributed to the final inclusion of the journal in the Web of Science in 2011. Finally, we introduce the four research articles of this 7th Dry Grassland Special Feature. Two of them are focusing on vegetation change and restoration issues of cryptogam-rich sand dunes in the Netherlands and calcareous grasslands in Bavaria (Germany), respectively. The others, dealing with siliceous grasslands in Hesse (central Germany) and the results of EDGG Research Expedition 2009 to Transylvania (Romania), focus on syntaxonomy.
- Nutrient-poor grasslands on siliceous soil in the lower Aar valley (Middle Hesse, Germany) – neglected vegetation types in the intersection range of four classes (2012)
- In the lower siliceous uplands of Central Europe, various types of nutrient-poor grasslands are widespread and grow intermingled. These species-rich grasslands, often dominated by taxa of the Festuca ovina aggregate, comprise various phytosociological classes. They are remnants of a historic rural lands - cape and are of conservation importance. Few studies on such grasslands are available and there has been disagreement in assigning them to appropriate habitat types or syntaxa. We investigated such nutrient-poor grasslands in the lower Aar valley (Middle Hesse, Rhenish Massif). We surveyed 104 vegetation plots distributed throughout the valley and identified syntaxa to (sub)association level. We carried out supervised classification combining cluster analysis, a priori assignment to classes based on prevailing diagnostic species, and regional refinement based on phi-value maximisation of the units. As a result, we classified five associations within four classes: Polytricho piliferi-Festucetum tenuifoliae/Galio harcynici-Deschampsietum flexuosae and Festuco rubrae-Genistelletum sagittalis (Calluno- Ulicetea), Jasiono montanae-Festucetum ovinae (Koelerio-Corynephoretea), Gentiano-Koelerietum pyramidatae (Festuco-Brometea) and Arrhenatheretum elatioris (Molinio-Arrhenatheretea). Ecologically, soil acidity (resulting from Ca concentrations of the bedrock) was the main cause of floristic dissimilarity of the grasslands and thus community differentiation. Many stands grew on soils with intermediate pH and showed a peculiar mixture of basiphilous and acidophilous species. We conclude that (i) our approach of supervised classification yields convincing reproducible results when a syntaxonomic system is adapted top-down to a geographically restricted area, (ii) nutrient-poor siliceous grasslands dominated by taxa of the Festuca ovina aggregate can be well assigned to ecologically meaningful syntaxa, and (iii) the nutrient-poor siliceous grasslands of the Lahn-Dill Highlands are of high conservation relevance and in urgent need of protection.