Potassium limits potential growth of bog vegetation under elevated atmospheric CO2 and N deposition

The free air carbon dioxide enrichment (FACE) and N deposition experiments on four ombrotrophic bogs in Finland, Sweden, the Netherlands and Switzerland, revealed that after three years of treatment: (1) elevated atmospheric CO₂ concentration had no significant effect on the biomass growth of Sphagnum and vascular species; and (2) increased N deposition reduced Sphagnum growth, because it increased the cover of vascular plants and the tall moss Polytrichum strictum, while vascular plant biomass growth was not affected. This paper focuses on water chemistry, plant nutrient content, and litter decomposition rates. Potassium limitation, or low supply of K and P, may have prevented a significant increase of Sphagnum growth under elevated CO₂ and N deposition. Vascular plant growth under elevated CO₂ and N deposition was also limited by K, or by K in combination with P or N (N in CO₂ experiment). Elevated CO₂ and N deposition had no effect on decomposition rates of Sphagnum and vascular plant litter. Aside from a possible effect of N deposition on light competition between species, we expect that elevated atmospheric CO₂ and N deposition concentrations will not affect Sphagnum and vascular plant growth in bogs of north‐west Europe due to K‐, or K in combination with N‐ or P‐, limited growth. For the same reason we expect no effect of elevated CO₂ and N deposition on litter decomposition. Net primary production of raised ombrotrophic bogs that are at or close to steady state, is regulated by input of nutrients through atmospheric deposition. Therefore, we hypothesize that the expected increase of plant growth under elevated CO₂ and N deposition is diminished by current levels of K (and to some extent P and N) in atmospheric deposition.     

MICROEVOLUTION AND PHENOTYPIC PLASTICITY IN DONAX SERRA RODING (BIVALVIA: DONACIDAE) ON HIGH ENERGY SANDY BEACHES

Morphological differences between populations of the wedge clamDonax serra inhabiting two different coasts and biogeographicregions of South Africa were investigated. Both adults and juvenilesoccupied different positions along the beach gradient dependingon the coast: on the southeast coast adults occurred in themid intertidal and juveniles and recruits were low intertidalto subtidal; on the west coast the zonation pattern was reversed.Not only adults but also juvenile clams had shapes differingsignificantly between the two coasts; west coast clams werethinner, rounder and had a higher body density than the southeastones-recruits were less dense in the former coast. Differencesin shell shape between coasts are probably the result of directionalselection on the adults with the microevolutionary changes beingmaintained by geographical isolation. Shell density, on theother hand, seems to be environmentally determined through physiologicalcontrol of shell calcification, i.e. more mobile intertidalclams having lower shell density than less mobile subtidal clams.Ontogenetic changes in shape and density are presumably adaptiveand appear to be related to mobility, i.e. the larger, heavierand denser adults being more stable in the substrate, and thesmaller, thinner and less dense juveniles being more mobileand dispersive. Phenotypic plasticity in present D. serra populationsis an important factor that enabled this species to occupy differenthabitats and biogeographic regions and to survive 5 millionyears of environmental changes. ¹ Present address: Laboratory for Ecology and Aquaculture, ZoologicalInstitute, Katholic Universiteit, Leuven, Naamsestraat 59 B-3000,Leuven, Belgium. E-mail: agsoares{at}eudoramail.com (Received 15 October 1997; accepted 5 January 1998)     

Predator-prey relationships and the evolution of colour polymorphism: a comparative analysis in diurnal raptors

Genetically based variation in coloration occurs in populations of many organisms belonging to various taxa, including birds, mammals, frogs, molluscs, insects and plants. Colour polymorphism has evolved in raptors more often than in any other group of birds, suggesting that predator–prey relationships was a driving evolutionary force. Individuals displaying a new invading colour morph may enjoy an initial foraging advantage because prey have difficulties in learning the colour of a rare morph (apostatic selection), or because morphs provide alternative foraging benefits allowing differently coloured individuals to exploit distinct food niches (disruptive selection). Plumage polymorphism should therefore have evolved in species that prey upon animals having the physiological ability to distinguish between differently coloured predators but also to flee once a predator has been detected. From this assumption, we can predict that closely related polymorphic and monomorphic species prey upon different animals. They may also differ in morphology, because foraging upon different prey may require different foraging modes, and in turn different morphological structures. We tested these two predictions in a comparative study of raptors. As expected, polymorphic and monomorphic species had a different diet, and there was a difference in wing length between polymorphic and monomorphic species within two genera ( Buteo and Accipiter ). Across all raptors for which phylogenetic relationships are known, polymorphic species preyed more often upon mammals than did monomorphic ones. These two types of raptor did not differ in the frequency of birds, insects and reptiles in their diets. We discuss these results in the light of the hypothesis that predator–prey relationships played a role in the evolution of colour polymorphism. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 565–578.     

High microbial activity on glaciers: importance to the global carbon cycle

Cryoconite holes, which can cover 0.1–10% of the surface area of glaciers, are small, water-filled depressions (typically <1 m in diameter and usually <0.5 m deep) that form on the surface of glaciers when solar-heated inorganic and organic debris melts into the ice. Recent studies show that cryoconites are colonized by a diverse range of microorganisms, including viruses, bacteria and algae. Whether microbial communities on the surface of glaciers are actively influencing biogeochemical cycles or are just present in a dormant state has been a matter of debate for long time. Here, we report primary production and community respiration of cryoconite holes upon glaciers in Svalbard, Greenland and the European Alps. Microbial activity in cryoconite holes is high despite maximum temperatures seldom exceeding 0.1 °C. In situ primary production and respiration in cryoconites during the summer is often comparable with that found in soils in warmer and nutrient richer regions. Considering only glacier areas outside Antarctica and a conservative average cryoconite distribution on glacial surfaces, we found that on a global basis cryoconite holes have the potential to fix as much as 64 Gg of carbon per year (i.e. 98 Gg of photosynthesis minus 34 Gg of community respiration). Most lakes and rivers are generally considered as heterotrophic systems, but our results suggest that glaciers, which contain 75% of the freshwater of the planet, are largely autotrophic systems.     

Modelling the spatial dynamics of a recovering species: the Grey Heron Ardea cinerea in France

In many countries, the implementation of measures to protect declining species has led to the recolonization of some areas by bird species within their historic range. There is, however, a lack of quantitative tools for exploring and projecting such large-scale dynamics. Here, we present an approach that makes use of both census and habitat suitability data and integrates them into a spatially explicit model of colonization dynamics (cellular automaton). The Grey Heron Ardea cinerea , which has recently recolonized much of France following legal protection measures, was used as a focal species. Data analysis allowed us to quantify the positive effects of habitat quality on the probability of colonization, and to uncover both positive and negative density-dependent colony settlement processes. Projective simulations then allowed us to determine an inflection point in global colonization dynamics and predict a significant reduction in the colonization rate during the next 50 years. This makes it possible to project the spatial distribution of the species at different timescales, and to estimate the carrying capacity of France for the species (around 1500 colonies).     

Life history of the Mato Grosso Antbird Cercomacra melanaria in the Brazilian Pantanal

Here we describe the habitat use, reproductive biology, diet and details of the life history of the Mato Grosso Antbird Cercomacra melanaria , one of the least studied Cercomacra species. We located 30 nests, of which 22 became active and were monitored. The nest consists of a deep cup, placed among dense tangles of vegetation, almost always in forests of Vochysia divergens ( Cambarazal ). Eggs are pinkish-cream coloured, covered with reddish brown to purple spots and blotches that are concentrated around its centre and larger end. Average nest success was 32%. The Mayfield method indicated daily survival rates during egg and nestling periods of 0.94 and 0.96, respectively, and a success rate of 26%. Examination of 24 stomach contents revealed a diet based exclusively on arthropods.     

Accumulation of polyunsaturated fatty acids by cladocerans: effects of taxonomy,temperature and food

1. Zooplankton are important in transferring dietary nutrients, including polyunsaturated fatty acids (PUFA), up through aquatic food webs. 2. We tested the hypothesis that the taxonomic composition of zooplankton affects the retention and subsequent transfer of PUFA from upwards through the food web. Using laboratory experiments, we investigated dietary PUFA accumulation and bioconversion capacities of six cladoceran species (Ceriodaphnia sp., Daphnia longispina, Daphnia magna, Daphnia pulex, Scapholeberis mucronata and Simocephalus vetulus) fed on two diets (Scenedesmus obliquus and Cryptomonas sp.) that differed in their PUFA profiles. We performed experiments at two different temperatures (14 and 20 °C) to assess the role of temperature in the trophic transfer of PUFA. 3. There was little variation in the concentrations of PUFA in these cladocerans which were controlled by dietary PUFA supply. Moreover, as expected, the concentrations of PUFA in all cladoceran species were higher at low temperature. 4. However, even if the composition of PUFA in the cladoceran species generally corresponded to that in their diet, preferential accumulation of some PUFA was recorded in all these taxa. When fed on a highly unsaturated fatty acid‐deficient diet, all the cladocerans showed some ability to convert C18‐PUFA into arachidonic acid and eicosapentaenoic acid. Interspecific variation in the ability to accumulate and bioconvert PUFA in cladocerans was more pronounced at low temperature (14 °C) for both diets. 5. Our results strongly suggest that in heterogeneous habitats with food partitioning between co‐existing cladocerans, foraging behaviour may affect the transfer of PUFA more strongly than interspecific variation in accumulating and/or bioconverting dietary PUFA.     

Electrophysiological characterization of pathways for K+ uptake into growing and non-growing leaf cells of barley

Potassium is a major osmolyte used by plant cells. The accumulation rates of K⁺ in cells may limit the rate of expansion. In the present study, we investigated the involvement of ion channels in K⁺ uptake using patch clamp technique. Ion currents were quantified in protoplasts of the elongation and emerged blade zone of the developing leaf 3 of barley ( Hordeum vulgare L.). A time-dependent inward-rectifying K⁺-selective current was observed almost exclusively in elongation zone protoplasts. The current showed characteristics typical of Shaker-type channels. Instantaneous inward current was highest in the epidermis of the emerged blade and selective for Na⁺ over K⁺. Selectivity disappeared, and currents decreased or remained the same, depending on tissue, in response to salt treatment. Net accumulation rates of K⁺ in cells calculated from patch clamp current–voltage curves exceeded rates calculated from membrane potential and K⁺ concentrations of cells measured in planta by factor 2.5–2.7 at physiological apoplastic K⁺ concentrations (10–100 m m ). It is concluded that under these conditions, K⁺ accumulation in growing barley leaf cells is not limited by transport properties of cells. Under saline conditions, down-regulation of voltage-independent channels may reduce the capacity for growth-related K⁺ accumulation.