Uptake of phosphate and inorganic nitrogen by a sediment-algal system in a subarctic lake

SUMMARY.

• 1 The uptake of phosphate and inorganic nitrogen by sediment and phytoplankton was studied under natural conditions (1977) and during lake fertilization with phosphorus and nitrogen (1978–79) in Lake Gunillajaure, a small, stratified, subarctic lake in northern Sweden. The experiments were performed in situ in plexiglass cylinders, to which additions of nutrients were made, and the uptake followed by consecutive sampling and analysis of the water phase.
• 2 Additions of HgCl₂ to the experimental vessels reduced the phosphate uptake to the sediment to less than 10% and it could therefore be concluded that the sediment uptake was mainly of biological nature.
• 3 Dark assimilation was 30–40% of that in light. Since light clearly stimulated the sediment uptake the epipelic algae were probably responsible.
• 4 The phosphate uptake to the sediment could be described by Michaelis-Menten kinetics and the calculated constants (V_max, ks) were very alike in 1977 and 1978 but appeared to have increased in 1979.
• 5 The sediment uptake of ammonium and nitrate was very slow indrcating that the epipelic algae were not nitrogen starved.
• 6 Even though the epipelic algae had a potential for efficient uptake of phosphorus, the phytoplankton took up 92–96% of the phosphate added to the lake on each fertilization occasion due to the relatively large water volume in the epilimnion in relation to the bottom area available for the epipelic algae.

     

New records of marine Tardigrada in the Mediterranean Sea

Meiofauna from Chafarinas archipelago (western Mediterranean, N. Africa) were studied, and marine Tardigrada were identified to species level. A total of 15 species, belonging to families Stygarctidae, Halechiniscidac (Subfamilies Halechiniscinae, Florarctinae, Styraconyxinae and Tanarctinae), Batillipedidae, and Echiniscoididae, were found for the first time from the Alboran Sea and southwestern Mediterranean area. Four species and one subspecies are new records for the Mediterranean Sea: I'ioractus acer, F. asper, P. stellatus, Actinarctus doryphorus and Echiniscoides sigismundi hispaniensis. The male of Floractus stellatus , previously unknown to science, is described. Many species have been recorded for the first time in different sedimentary environments, such as midlittoral pools, very shallow gravels, pools in a mixed rocky environment or between Posidonia oceanica meadows, 'Amphioxus' gravels, and coastal detritic.     

New chromosome counts in the genus Cousinia and the related genus Schmalhausenia (Asteraceae, Cardueae)

Twenty chromosome counts are reported in the genus Cousinia and the monotypic genus Schmalhausenia , which are part of the Arctium group, from Armenia, Iran, Kazakhstan and Uzbekistan. Twelve are new and eight provide confirmation of scarce or disputable previous data. The correlation between karyological data, pollen type and molecular phylogeny is very close, and on this basis two main groups can be defined. One is the arctioid group, which comprises the genera Arctium and Schmalhausenia , and a small part of the genus Cousinia , with x  = 18. The other is the genus Cousinia s.s. , with a dysploid series ranging from x  = 13–11. Some considerations on the chromosomal evolution in the group are made.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Socety , 2003, 143 , 411–418.     

Biological activity of aryl hydrocarbon receptor ligands in sediments from remote European lakes

1. Sediment extracts from 63 European remote lakes were tested for the presence of ligands of the aryl hydrocarbon receptor (AhR), using a yeast-based bioassay. The lakes belong to different European mountain regions in Central Norway, Scotland, Piedmont (Italy), Tyrol (Austria and Italy) and the Julian Alps (Slovenia).
2. AhR ligand activity varied about 40-fold among the examined lakes, with Scotland having the highest proportion of lakes with high AhR ligand activity, whereas samples with low AhR ligand activity predominate in the Julian Alps.
3. AhR ligand activity in sediment samples correlated with the concentration of several environmentally relevant compounds, including polycyclic aromatic hydrocarbons, hexachlorobenzene and several polychlorobiphenyl ether congeners. These correlations suggest an anthropogenic origin for the detected AhR ligands, rather than being generated from natural processes.
4. We conclude that pollutants deposited in remote lakes by atmospheric processes are active AhR ligands at the concentrations found in these lakes. Given the high toxicity associated with ectopic activation of AhR in different animal systems, this activity may represent a significant risk for the exposed fauna.     

New chromosome counts in the Centaurea Jacea group (Asteraceae, Cardueae) and some related taxa

Twenty-seven chromosome counts are reported in 23 species of the genus Centaurea , mostly eastern endemic species of the Jacea group, which has become the core of the re-defined genus Centaurea . Twenty reports are new, one is a correction of a previous count, one is a confirmation of limited previous data and one represents a new basic number in the Centaureinae. The prevalence of the basic chromosome number x  = 9 among the Eastern sections of the Jacea group is confirmed, together with the close correlation between karyological data and classification of the genus. Two alternative hypotheses on the aberrant chromosome number (for the Centaureinae) found in C. behen are proposed. One of them, if verified, would confirm that a cycle of polyploidy and descending dysploidy is a key mechanism in the speciation of the group.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 345–352.     

Foliar freezing resistance of Australian alpine plants over the growing season

We assessed the freezing resistance of leaves ex situ of 25 Australian alpine plant species. We compared the freezing resistance of forb, graminoid and shrub species from three alpine summits of different altitudes; from a low altitude site just above treeline, to a fully alpine tundra site. Foliar freezing resistance (LT₅₀) in spring varied from ?5.9°C to ?18.7°C and standardized LT₅₀ values within species were significantly related to site altitude. Additionally, when comparing all the species in the study, freezing resistance was significantly related to site; the LT₅₀ of samples from a low‐altitude summit (1696 m) were significantly lower than those of samples from mid‐ (1805 m) and high‐altitude (1860 m) summits. The LT₅₀ of juvenile foliage did not differ significantly from that of adult foliage. Shrubs were highly resistant to freezing. At the highest summit, we examined the course of seasonal freezing resistance from early summer to early autumn across three alpine plant communities that differed in the time of natural snowmelt; from sheltered (snowpatch) to exposed (open heath). No differences in freezing resistance over the growing season were detected for exposed or sheltered communities and there were no consistent trends indicating frost hardening over the growing season. Overall, the common Australian alpine species we investigated appear well adapted to freezing conditions throughout the snow‐free growing season. We have no evidence to suggest that freezing temperatures soon after snowmelt in spring are especially damaging to the alpine plants at these summits.     

New chromosome counts in the genus Centaurea (Asteraceae) from Turkey

Twenty‐two chromosome counts are reported in 16 species, four subspecies and two varieties of the genus Centaurea. These are mostly Turkish local endemics of section Cheirolepis, a complicated group from the Eastern clade of the Jacea group. Twenty‐one reports are new. Prevalence of the basic chromosome number x = 9 among the eastern sections of the Jacea group is confirmed. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 280–286.     

Contribution to the karyological knowledge of Echinops (Asteraceae, Cardueae) and related genera

Twenty-six chromosome counts were made of several genera of the tribe Cardueae from various European and Asian provenances: Acantholepis (one species studied), Amphoricarpus (1), Chardinia (1), Echinops (14 species, 15 populations), Siebera (1), Staehelina (3) and Xeranthemum (4). Eleven of the reports are made for the first time, ten confirm previous counts, while the remainder report disparities with earlier records. The existence of different basic chromosome numbers and ploidy levels suggests dysploidy and polyploidy as the main mechanisms of chromosomal evolution in the taxa considered.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 337−344.     

Karyological evolution in Rhaponticum Vaill. (Asteraceae, Cardueae) and related genera

Chromosome counts are reported in 29 populations representing 20 species and one subspecies of the genera Callicephalus (one sp.), Klasea (seven spp.), Myopordon (two spp.), Oligochaeta (one sp.), and Rhaponticum (nine spp., one ssp.). Eleven reports are new, the others supplement limited previous data. New and published cytological data are summarized and evaluated critically in light of current taxonomic treatments and evolutionary hypotheses. Basic chromosome numbers are a valuable source of taxonomic information and relate well to the phylogeny. They are quite conserved in Klasea (only x  = 15), the sister group of the remaining genera, and in the early branching genera of the Rhaponticum group ( x  = 14 for Centaurothamnus and Callicephalus ). However, a more complex pattern of genome evolution is present among the more derived clades, Oligochaeta plus Myopordon ( x  = 12, 14) and the genus Rhaponticum ( x  = 12, 13). The occurrence of x  = 12 in Oligochaeta divaricata and Rhaponticum carthamoides seems to be the result of a recent event of chromosome fusion, as suggested by the fragility of particularly long pairs of chromosomes. The use of chromomycin staining, including an enzymatic digestion step that facilitates spreading and permits a reduction of potential fragmentation, only partially resolves this problem.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 193–201.