Stream characteristics and their implications for the protection of riparian fens and meadows

1. Running waters, including associated riparian areas, are embraced by international legal frameworks outlining targets for the preservation, protection and improvement of the quality of the environment. Interactions between stream and river processes and riparian habitats have not received much attention in the management of stream ecosystems, and integrated measures that consider both the ecological status of streams and rivers (sensu EU Water Framework Directive, WFD) and the conservation status of riparian habitats and species (sensu EU Habitats Directive, HD) are rare. 2. Here, we analysed the influence of stream size, morphology and chemical water characteristics for the distribution of water‐dependent terrestrial habitat types, i.e. alkaline fens, periodically inundated meadows and meadows in riparian areas in Denmark using an extensive data set covering a total of 254 stream reaches. A species‐based classification model was used to translate species lists into a standardised interpretation of habitat types protected by the HD in Denmark. 3. No size dependency was found regarding the distribution of fen and meadow vegetation. Instead, the distribution of fen and meadow vegetation was strongly affected by the morphology of the streams. Alkaline fens, periodically inundated meadows and meadows occurred six, five and four times, respectively, less frequently along channelised compared with natural stream reaches. Our results indicate that stream channelisation strongly interfered with the natural hydrology of riparian areas, affecting conditions needed to sustain protected fen and meadow communities. 4. We also found that water chemistry strongly influenced the occurrence of fen and meadow vegetation in riparian areas. The probability of finding fen and meadow vegetation was reduced when total phosphorus (TP) concentration exceeded 40–50 μg P L^?1, whereas meadow vegetation responded less strongly to TP. 5. Our findings highlight the importance of restoring hydrology of riparian areas to improve conditions for fen and meadow vegetation, but also that the water chemistry should be considered when measures that increase hydrological connectivity result in an increase in the probability of flooding.     

Influence of quantity and lability of sediment organic matter on the biomass of two isoetids,Littorella uniflora and Echinodorus repens

1. Despite real improvement in the water quality of many previously eutrophic lakes, the recovery of submerged vegetation has been poor. This lack of recovery is possibly caused by the accumulation of organic matter on the top layer of the sediment, which is produced under eutrophic conditions. Hence, our objective was to study the combined effects of quantity and lability of sediment organic matter on the biomass of Echinodorus repens and Littorella uniflora and on the force required to uproot plants of L. uniflora. 2. Lake sediments, rich in organic matter, were collected from four lakes, two with healthy populations of isoetids and two from which isoetids had disappeared. The four lake sediments were mixed with sand to prepare a range of experimental sediments that differed in quantity and lability of sediment organic matter. Two isoetid species, E. repens and L. uniflora, were grown in these sediments for 8 weeks. Sediment quality parameters, including elemental composition, nutrient availability and mineralisation rates, were determined on the raw sources of sediment from the lakes. Porewater and surface water were analysed for the chemical composition in all mixtures. At the end of the experiment, plants were harvested and their biomass, tissue nutrient concentration and (for L. uniflora) uprooting force were measured. 3. For both species, all plants survived and showed no signs of stress on all types of sediment. The biomass of E. repens increased as the fraction of organic matter was increased (from 6 to 39% of organic content, depending upon sediment type). However, in some of the sediment types, a higher fraction of organic matter led to a decline in biomass. The biomass of L. uniflora was less responsive to organic content and was decreased significantly only when the least labile sediment source was used to create the gradient of organic matter. The increase in shoot biomass for both species was closely related to higher CO₂ concentrations in the porewater of the sediment. The force required to uproot L. uniflora plants over a range of sediment organic matter fitted a Gaussian model; it reached a maximum at around 15% organic matter and declined significantly above that. 4. Increasing organic matter content of the sediment increased the biomass of isoetid plants, as the positive effects of higher CO₂ production outweighed the negative effects of low oxygen concentration in more (labile) organic sediments. However, sediment organic matter can adversely affect isoetid survival by promoting the uprooting of plants.     

Orchids in the torrent: on the circumscription,conservation and rheophytic habit of Epipactis flava

The systematically difficult genus Epipactis (Orchidaceae) is often subdivided into two sections: Epipactis and Arthrochilium. Until now, the latter has attracted much less taxonomic attention than the former, but here we reassess the alleged distinction of two rare and nationally endangered taxa from tropical Asia (E. flava, E. atromarginata), based on morphological examination of live plants in situ in northern Thailand and of herbarium specimens from the entire range of the complex (Thailand, Laos and Vietnam). As the variation in vegetative and floral dimensions, flower colour and labellum morphology broadly overlaps between the two taxa, we merge them under the oldest valid name at species level, E. flava. Geomorphological features of our three study sites in Thailand and high shared occurrence of previously confirmed rheophytes among the accompanying species indicate that E. flava is itself rheophytic (a very rare feature in the Orchidaceae). Possible adaptations of E. flava to its rheophytic lifestyle are discussed. Among these, the formation of pure stands through dense clonal growth involving a creeping rhizome places E. flava as a ‘mat‐rooted rheophytic landplant’ (sensu van Steenis). Combining taxonomic, distributional and ecological data, we discuss the occurrence of this stream‐inhabiting Epipactis in a conservation context. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 358–370.     

Introgression and phylogeography of Betula nana (diploid), B. pubescens (tetraploid) and their triploid hybrids in Iceland inferred from cpDNA haplotype variation

Aim The objective was to find direct genetic evidence supporting introgressive hybridization between tetraploid tree birch (Betula pubescens) and diploid dwarf birch (B. nana), via triploid hybrids, and to investigate an association between the introgression and phylogeographical distribution of Icelandic birch. Location Samples were collected from 463 trees in 12 woodlands in Iceland and eight locations in Norway, Sweden, Scotland and Greenland. Methods Ploidy status of individual trees was determined by chromosome counting. Variation in the chloroplast genome was assessed using polymerase chain reaction‐restriction fragment length polymorphism. The geographical distribution of the haplotypes was mapped. The haplotype variation and introgression ratios (IG) were analysed statistically. Results Thirteen haplotypes were identified among Icelandic samples. The most common haplotype (T, 49% occurrence) was present in all ploidy groups and in all woodlands. All common haplotypes were shared between the triploid group and the parental species, indicating introgressive hybridization. This was supported by the statistical analysis of IG indices and the variation components. Considerable differences existed among samples, shaped by isolation by distance and local introgression. An east–west phylogeographical distribution in Iceland was observed. Main conclusions Despite extensive introgression across species and ploidy levels, a biogeographical pattern has been observed, and this may indicate different population histories or multiple origins of Icelandic birch. The chloroplast haplotype diversity found in Iceland resembles that found in birch populations from northern Scandinavia.     

Apochromic populations of Dactylorhiza incarnata s.l. (Orchidaceae): diversity and systematic significance as revealed by allozyme markers and morphology

Apochromic forms of the Eurasian Dactylorhiza incarnata s.l. were studied in northern Europe to reveal their genetic (allozyme) and morphological diversity and to assess their systematic significance. The study included eight localities with sympatric populations of plants with anthocyanin‐pigmented and apochromic flowers. Parallel samples of the two morphs were taken from each locality. Genetic variation was only found at the allozyme loci pgd, pgi and ugpp. Statistically significant differences in allele frequencies between the two colour morphs were found in two localities and demonstrate that the occurrence of apochromic individuals in D. incarnata s.l. is not always because of spontaneous mutation. At least in some localities the apochromic plants form distinct breeding groups (but local populations of different colour morphs may also be composed of several more or less distinct breeding groups). Based on molecular and morphometric data, it is proposed that the apochromic study populations from calcareous fens should be referred to D. incarnata var. ochroleuca, whereas the apochromic study populations from non‐calcareous fens are better treated as aberrant local populations of var. incarnata s.l. Possible evolutionary patterns and processes are discussed and guidelines for identification of var. ochroleuca from morphological features are given. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 396–407.     

On the distinction of Dactylorhiza baltica and D. pardalina (Orchidaceae) and the systematic affinities of geographically intermediate populations

The eastern European Dactylorhiza baltica (Klinge) N. I. Orlova and the western European D. pardalina (Pugsl.) Aver. (= D. praetermissa var. junialis (Verm.) Sengh) are usually considered to have non-overlapping geographic distributions, for which reason it has rarely been realized that they are morphologically similar. They have not previously been thoroughly compared by molecular methods, and no existing flora or revision has convincingly demonstrated that they can be distinguished by morphological characters. In reality, they might be 'political' rather than natural taxa. Prompted by the recent discovery of geographically intermediate populations (in eastern Denmark), originally identified as D. baltica , we have addressed this problem by analysis of morphometric data as well as molecular data from allozyme markers, plastid haplotypes, nuclear ITS alleles and nuclear microsatellites. Dactylorhiza baltica and D. pardalina turned out to be clearly distinguished genetically, and although they are morphologically similar, a few characters were identified that distinguish with 81–85% certainty between the two taxa. Molecular and morphometric data place the geographically intermediate populations in D. pardalina . Both taxa were confirmed to be allotetraploids combining diploid genomes from the D. incarnata s.l. and D. maculata s.l. lineages, and they should therefore be recognized as infraspecic taxa under D. majalis s.l. Thus, D. baltica should be called D. majalis subsp. baltica ; D. pardalina is identical with D. praetermissa var. junialis , but the nomenclatural consequences for D. praetermissa , if treated as subspecies under D. majalis , are still unresolved.     

Acclimation of a terrestrial plant to submergence facilitates gas exchange under water

Flooding imposes stress upon terrestrial plants since it severely hampers gas exchange rates between the shoot and the environment. The resulting oxygen deficiency is considered to be the major problem for submerged plants. Oxygen microelectrode studies have, however, shown that aquatic plants maintain relatively high internal oxygen pressures under water, and even may release oxygen via the roots into the sediment, also in dark. Based on these results, we challenge the dogma that oxygen pressures in submerged terrestrial plants immediately drop to levels at which aerobic respiration is impaired. The present study demonstrates that the internal oxygen pressure in the petioles of Rumex palustris plants under water is indeed well above the critical oxygen pressure for aerobic respiration, provided that the air‐saturated water is not completely stagnant. The beneficial effect of shoot acclimation of this terrestrial plant species to submergence for gas exchange capacity is also shown. Shoot acclimation to submergence involved a reduction of the diffusion resistance to gases, which was not only functional by increasing diffusion of oxygen into the plant, but also by increasing influx of CO₂, which enhances underwater photosynthesis.     

Patterns of animal dispersal, vicariance and divsrsification in the Holarctic

We analysed patterns of animal dispersal, vicariance and diversification in the Holarctic based on complete phylogenies of 57 extant non‐marine taxa, together comprising 770 species, documenting biogeographic events from the Late Mesozoic to the present. Four major areas, each corresponding to a historically persistent landmass, were used in the analyses: eastern Nearctic (EN), western Nearctic (WN), eastern Palaeoarctic (EP) and western Palaeoarctic (WP). Parsimony‐based tree fitting showed that there is no significantly supported general area cladogram for the dataset. Yet, distributions are strongly phylogenetically conserved, as revealed by dispersal‐vicariance analysis (DIVA). DIVA‐based permutation tests were used to pinpoint phylogenetically determined biogeographic patterns. Consistent with expectations, continental dispersals (WP?EP and WN?EN) are significantly more common than palaeocontinental dispersals (WN?EP and EN?WP), which in turn are more common than disjunct dispersals (EN?EP and WN?WP). There is significant dispersal asymmetry both within the Nearctic (WN→EN more common than EN→WN) and the Palaeoarctic (EP→WP more common than WP→EP). Cross‐Beringian faunal connections have traditionally been emphasized but are not more important than cross‐Atlantic connections in our data set. To analyse changes over time, we sorted biogeographic events into four major time periods using fossil, biogeographic and molecular evidence combined with a ‘branching clock’. These analyses show that trans‐Atlantic distributions (EN‐WP) were common in the Early‐Mid Tertiary (70‐20 Myr), whereas trans‐Beringian distributions (WN‐EP) were rare in that period. Most EN‐EP disjunctions date back to the Early Tertiary (70‐45 Myr), suggesting that they resulted from division of cross‐Atlantic rather than cross‐Beringian distributions. Diversification in WN and WP increased in the Quaternary (< 3 Myr), whereas in EP and EN it decreased from a maximum in the Early‐Mid Tertiary.