Habitat preferences as related to the prolonged dormancy of perennial herbs and ferns

Prolonged dormancy (hereafter dormancy), a phenomenon in which a perennial herbaceous plant does not sprout for one or more years, is examined. The phenomenon may be more frequent than stated so far and discovery of its role in plant life history and performance is still underway. Data from published papers was reviewed and all known species exhibiting dormancy were analysed from the aspect of species ecological values. Adaptation to environmental factors (light, moisture, pH and nitrogen as estimated by Ellenberg indicator values) influences the maximum duration of dormancy. A higher proportion of plants are dormant in species that prefer to grow in good light conditions, dry sites and infertile soil. The duration of dormant period is longer in species that prefer to grow in dry sites and/or calcareous soils. A range of factors, we believe, control plant behaviour, however, it is suggested that environmental stress is the principal factor inducing dormancy.     

Weather and herbivores influence fertility in the endangered fern Botrychium multifidum (S.G. Gmel.) Rupr

Fluctuations in local weather conditions and other stochastic processes are important factors affecting species population persistence. We studied two differently sized populations of the rare and declining fern species Botrychium multifidum for 4 and 5 years, respectively. Individually marked plants in permanent plots were followed to detect trends in population size, reproductive success and dormancy in relation to local precipitation and temperature. Our applied logistic regression model suggests that the shortage of precipitation during summer decreases fertility in the next year in both populations. Invertebrate herbivory of the fertile part of the plant additionally diminishes the output of spores. We found the population size to be stable with a very low percentage of each population composed of juvenile plants. Stochastic processes and low recruitment could easily lead to the extinction of these populations.     

High-resolution spectroscopic study of pore-water dissolved organic matter in Holocene sediments of Lake Peipsi (Estonia/Russia)

Ultraviolet–visible absorption and fluorescence spectroscopies allow simultaneous detection of several organic substances. These spectra also contain information on whether the organic matter is produced in the water body or in its catchment. In this work various spectral indices, which are widely used in aquatic studies to determine humic substances, proteinaceous matter, chlorophyllous pigments and the origin (autochthonous versus allochthonous) of organic matter, were applied to track changes in a Holocene record from the large and shallow northern temperate Lake Peipsi (Estonia/Russia) at a high-resolution scale. Absorption and three-dimensional fluorescence spectra of the organic matter fraction dissolved in sediment pore water (pDOM) were analysed. In addition to the spectral measurements of pDOM, the sediment samples were analysed for main constituents (water and organic and mineral matter) and magnetic properties. The core chronology was established by nine radiocarbon datings. Temporal changes in pDOM in the record were quite variable; however, three periods in the development of the lake can be distinguished: a 2500 yr period in the early Holocene and a 2500 yr period in the late Holocene, when drastic changes in the accumulated matter occurred, and a rather stable 5000 yr period in between. We postulate that the changes over the period in the early Holocene reflect a rise of water level in the lake; the oscillations over the relatively steady period were probably caused by climatic factors, and alterations over the period in the late Holocene were due to the expansion of agricultural activity in the lake catchment. Our findings indicate that the use of spectral indices in palaeoinvestigations offers valuable information for reconstructing natural and human-induced developments of lakes.     

Drastic changes in lake ecosystem development as a consequence of flax retting: a multiproxy palaeolimnological study of Lake Kooraste Linajärv,Estonia

This study demonstrates the power of multiproxy palaeolimnological analyses in investigating environmental changes in the Lake Kooraste Linajärv ecosystem through historical time in response to flax retting. Flax retting history was proven by applying pollen and macrofossil evidence and by using several biotic and geochemical proxies on a sediment core. Continuous findings of flax pollen and macrofossil remains in lake sediments were considered as strong evidence for the occurrence of retting. Analyses of the well-dated sediment core show the consequences of flax retting in the lake. As a result, the once clear soft water oligotrophic endorheic lake with limited sedimentation has turned into a hypertrophic high-sedimentation lake with anoxic bottom water, strong stratification and intense water blooms. Despite the fact that flax retting was forbidden in Estonia around ad 1950s and retting has not occurred over the last six decades, anthropogenic alterations were so pervasive in the past, that they have prevented any lake water improvements until the present-day.     

Pattern of some Silurian bioevents

The best‐known Silurian bioevent occurred at the end of the Wenlock: the lundgreni event, together with the nassa‐ludensis crisis, was established among planktic graptolites. The East Baltic data show several peaks of high diversity (especially triangulatus, turriculatus, scanicus zones) and three levels of low diversity of graptolites (antennularius, radians, ludensis zones). These are more or less coincident with sea‐level changes. Energetic innovation of the shallow shelf corals started in the early Silurian. The late Wenlock regression seems not to affect them seriously but the late Silurian decline coincides with the aridization of the climate and a regression of the shelf seas. The Agnatha had strong radiations in the Wenlock (ludensis Zone) and Ludlow (leintwardinensis Zone), the fishes in the Pridoli. Many Silurian vertebrates were long‐ranging and extinction rate was relatively low; only at the late leintwardinensis level and in the latest Ludlow did considerable extinctions occur.     

Necessity and reality of monitoring threatened European vascular plants

Species monitoring is the regular observation and recording of changes in status and trend of species in a certain territory. The primary purpose of monitoring is to collect information that can be used to examine the outcomes of management actions and to guide management decisions. Here, we analyze plant species monitoring to provide a first overview on efforts made to monitor trends in vascular plant biodiversity in Europe. Our study is based on an assessment of 63 plant monitoring schemes from Europe (collected into a database “DaEuMon”), and 33 schemes found with literature screening. Altogether, the monitoring schemes cover 354 vascular plant species, of which 69 are listed in Annex II of the EU Habitats Directive (= EU protected species; Annex II includes 420 species). In most cases, an EU protected plant species occurs in 3 countries but is monitored in only 1 country. Scientific interest was the main reason for launching a monitoring scheme in 21% of the schemes from the database, but in 58% of the schemes from the literature survey. The current schemes collect insufficient data particularly on the dynamics of the extent and distribution pattern of species. We conclude that planning to publish monitoring data when designing a scheme would improve the quality and general effect of monitoring programs. The needs to cover the taxonomic diversity and the integration of different scales, as well as the inclusion of monitoring in the context of different types of sustainable management would require a strong emphasis in the development of monitoring schemes.     

Detection of cellulolytic activity of bacteria and fungi growing on agar surfaces

Summary Cellulolytic activity of four fungal species growing on solid medium containing acid-swollen cellulose could be detected much more easily if fungal growth was partly inhibited by the detergent Triton X-100. The dye, aniline blue-black, did not affect growth but increased the sensitivity of detection of cellulolytic activity of both fungi and bacteria. Separating fungi from cellulose fibres by a layer of agar or by filters showed that cell-fibre contact is not necessary for cellulose degradation. Such degradation is clearer when contact is prevented.     

Response of calcareous grassland vegetation to mowing and fluctuating weather conditions

Question: What determines the balance between the cover values of vascular plants, lichens and mosses in dry calcareous grassland communities? Location: Western Estonia. Methods: A five‐year (2001–2005) study was conducted in a dry calcareous grassland. The cover of mosses, lichens and vascular plants and all moss species was recorded in permanent plots. Vascular plants were cut in half of the plots. Data from a nearby weather station were used to calculate mean values of different weather parameters and a summer moisture index for the study years. Results: Significant differences in cover values between years were found. The fluctuations of total moss cover and the cover of the dominating moss species Ctenidium molluscum followed changes in annual precipitation. Both cover values were highest in years with high precipitation. The cover change of vascular plants was best characterized by the moisture index of the growth period (three summer months). Summers with high moisture indexes facilitated vascular plant and lichen growth. Annual precipitation and the cover of mosses had a negative influence on the cover of vascular plants. The cutting of vascular plants did not have a significant effect on moss and lichen cover. Conclusions: 1. On dry calcareous grasslands the growth of mosses is enhanced by high annual precipitation, while the growth of vascular plants and lichens is influenced rather by the high summer moisture index. The cover of vascular plants is inhibited by the large moss cover. 2. Mowing of vascular plants does not influence the cover of mosses and lichens.     

The structure of the organ of bellonci of the syncarid crustacean,Anaspides tasmaniae (Thomson)

Summary The organ of Bellonci of Anaspides tasmaniae (Thomson) (Crustacea, Syncarida) is described light and electron microscopically, and a few histochemical tests are reported. Located ventrally in the eyestalk below the medulla interna, the organ is composed of a number of cavities. These are similar in structure in their contents and associated cellular components, which include two types of glia cells delimiting each cavity and the terminal parts of a few dendrites. Each dendrite usually bears two cilia, which project into the cavity where they split up into numerous branches. The organ is supplied by three nerve tracts: two from the medulla terminalis and one from the medulla interna. The sensory pore, which is innervated from the medulla interna, is not closely associated with the organ of Bellonci in Anaspides. No marked secretory activity is detectable by histochemical or ultrastructural observations. It is thought that the organ has a sensory function.This investigation was supported by a grant (to T.K.) from Helge Ax:son Johnsons Stiftelse. One of us (P.S.L.) was on sabbatical leave from the University of Tasmania.     

Recent patterns of sediment accumulation in a small closed eutrophic lake revealed by the sediment records

A short-core palaeolimnological investigation was undertaken with the aim ofacquiring knowledge of sediment deposition. Analyses of the lithological composition of sediments from the whole-lake basin were performed on the small eutrophic L. Linajärv (northern Estonia) and the concentrations of mineral and organic matter were measured on 647 sub-samples from 14 sediment cores. The accumulation rate of the sediment sequences was established and C/N ratios of organic matter in some cores were recorded. Results indicate that the water depth, basin slopes and distance to the shore have the most important impact on the physical sediment properties. It was shown that variations in the mineral matter concentrations were influenced by the changes in deposition conditions in the areas with steep slopes. The study indicated that more objective information about the sedimentation mechanisms is obtained using analysis of the concentration ratio of mineral and organic matter since it reduces the implied role of diagenetic compaction.