Methane emission from Siberian arctic polygonal tundra: eddy covariance measurements and modeling

Eddy covariance measurements of methane flux were carried out in an arctic tundra landscape in the central Lena River Delta at 72°N. The measurements covered the seasonal course of mid‐summer to early winter in 2003 and early spring to mid‐summer in 2004, including the periods of spring thaw and autumnal freeze back. The study site is characterized by very cold and deep permafrost and a continental climate with a mean annual air temperature of ?14.7 °C. The surface is characterized by wet polygonal tundra, with a micro‐relief consisting of raised moderately dry sites, depressed wet sites, polygonal ponds, and lakes. We found relatively low fluxes of typically 30 mg CH₄ m^?2 day^?1 during mid‐summer and identified soil temperature and near‐surface atmospheric turbulence as the factors controlling methane emission. The influence of atmospheric turbulence was attributed to the high coverage of open water surfaces in the tundra. The soil thaw depth and water table position were found to have no clear effect on methane fluxes. The excess emission during spring thaw was estimated to be about 3% of the total flux measured during June–October. Winter emissions were modeled based on the functional relationships found in the measured data. The annual methane emission was estimated to be 3.15 g m^?2. This is low compared with values reported for similar ecosystems. Reason for this were thought to be the very low permafrost temperature in the study region, the sandy soil texture and low bio‐availability of nutrients in the soils, and the high surface coverage of moist to dry micro‐sites. The methane emission accounted for about 14% of the annual ecosystem carbon balance. Considering the global warming potential of methane, the methane emission turned the tundra into an effective greenhouse gas source.     

Geographical variation in patterns of parentage and relatedness in the co‐operatively breeding Ground Tit Parus humilis

The Ground Tit is a large parid species endemic to the Tibetan Plateau. Here we describe its genetic breeding system based on 2 years of fieldwork on a population from Damshung, Tibet. Genetic relatedness and parentage were analysed using 16 microsatellite markers and sex was determined with a marker on the Z and W chromosomes. We established that 16 of 75 families (21%) were assisted by one or occasionally two male helpers, which in most cases were young from a previous brood of one or both of the breeding adults. The helpers typically stayed with their families throughout the breeding season. Helpers never obtained any paternity in their own families, but one helper was identified as the sire in the only instance of extra‐group (and extra‐pair) parentage detected. Thus, the level of extra‐group/extra‐pair parentage appears to be very low in this Ground Tit population, and sharing of reproduction within family groups is apparently absent. Our results contrast with the findings from another Ground Tit population in Gansu, further northeast in China, with respect to both the number and sex of helpers and the division of parentage within and among family groups. In Gansu, helpers regularly produced offspring and both extra‐pair and extra‐group paternity as well as maternity (egg dumping) was common. Differences in family structure, philopatry, territoriality and potential inclusive fitness benefits can probably explain this contrast, and are likely to reflect the relative costs and benefits of co‐operative breeding.     

Net primary production and light use efficiency in a mixed coniferous forest in Sweden

Simple light use efficiency (ɛ) models of net primary production (NPP) have recently been given great attention (NPP = ɛ × absorbed photosynthetically active radiation). The underlying relationships have, however, not been much studied on a time step less than a month. In this study daily NPP was estimated as the sum of net ecosystem exchange (NEE) and heterotrophic respiration (R_h) of a mixed pine and spruce forest in Sweden. NEE was measured by eddy correlation technique and R_h was estimated from measurements of forest floor respiration (R_f) and the root share of R_f. The total yearly NPP was on average 810 g C m⁻² year⁻¹ for 3 years and yearly ɛ was between 0.58 and 0.71 g C MJ⁻¹, which is high in comparison with other studies. There was a seasonal trend in ɛ with a relatively constant level of approximately 0.90 g C MJ⁻¹ from April to September Daily NPP did not increase for daily intercepted radiation above 6 MJ m⁻² d⁻¹, indicating that between-years variation in NPP is not directly dependent on total Q_i. The light was most efficiently used at an average daytime temperature of around 15 °C. At daytime vapour pressure deficit above 1400 Pa ɛ was reduced by approximately 50%.     

Microbial leaf degraders in boreal streams: bringing together stochastic and deterministic regulators of community composition

1. Leaves that fall into the water represent a new habitat for microorganisms to colonise in streams, providing an opportunity to study colonisation and the subsequent regulation of community structure. We explored community composition of bacteria and fungi on decomposing alder leaves in nine streams in central Sweden, and describe their relationship with environmental variables. Succession of the microbial community was studied in one of the streams for 118 days. Microbial community composition was examined by denaturing gradient gel electrophoresis on replicate samples of leaves from each stream. 2. During succession in one stream, maximum taxon richness was reached after 34 days for bacteria and 20 days for fungi respectively. Replicate samples within this stream differed between each other earlier in colonisation, while subsequently such variation among replicate communities was low and remained stable for several weeks. Replicate samples taken from all the nine streams after 34 days of succession showed striking similarities in microbial communities within‐streams, although communities differed more strongly between streams. 3. Canonical analysis of microbial communities and environmental variables revealed that water chemistry had a significant influence on community composition. This influence was superimposed on a statistical relationship between the properties of stream catchments and microbial community composition. 4. The catchment regulates microbial communities in two different ways. It harbours the species pool from which the in‐stream microbial community is drawn and it governs stream chemistry and the composition of organic substrates that further shape the communities. We suggest that there is a random element to colonisation early in succession, whereas other factors such as species interactions, stream chemistry and organic substrate properties, result in a more deterministic regulation of communities during later stages.     

Homologies in Cambrian Onychophora

Marine animals related to Recent onychophorans form a significant component in Cambrian faunas. Twelve characters are analysed for homologies in the seven best known Cambrian onychophorans. New morphological evidence and homology analyses for several characters indicate an anteroposterior reversal of Hallucigenia and Microdictyon . Proposed expansion of the trunk in Microdietyon during compaction is rejected. A jaw is tentatively identified in Onychodictyon . The shape of the annulations and the disposition of the tenth leg pair in Aysheaia are reinterpreted, and the suggestion of two somites to the first appendage pair is rejected. A suggested morphocline may mirror the phylogeny of the group. The taxonomic confusion surrounding the supposed radiolarian family Eoconchariidae is cleared     

Quantification of deep and superficial sensibility in saline-induced muscle pain-a psychophysical study

The aim of the present study was to study the sensibility in the area of saline-induced muscle pain. In three experiments, ten subjects were exposed to computer-controlled infusion of 0.5 ml isotonic (0.9%) or hypertonic (9%) saline into the anterior tibial muscle. The pain intensity was assessed on a visual analogue scale (VAS). The pain threshold (PT) to pressure and electrical stimulation in muscle and subcutaneous tissues was determined. Three experiments were performed in which infusion of hypertonic saline produced significantly higher VAS scores than isotonic saline. In all three experiments, there was no significant difference in PT obtained after infusion of isotonic saline compared with infusion of hypertonic saline. In experiment 1, the PT was determined at the infusion site and 4 cm from the infusion site. At the infusion site, the pressure PT decreased (- 19 2%) 1, 3, 5, 7 and 9 min after infusion of isotonic and hypertonic saline, but remained unchanged 4 cm from the infusion site. The intramuscular electrical PT at the infusion site and 4 cm from the infusion site increased significantly (29 6%) 5, 7 and 9 min after saline infusion. In experiment 2, the pressure PT and the intramuscular electrical PT were recorded after two infusions of saline separated by 1 day. The day after the first infusion, the pressure PT was decreased compared with the PT before the first infusion, but the electrical PT was not affected. Moreover, the hypertonic saline infusion given on the second day produced significantly higher (130 50%) VAS scores than the infusion given on the first day. In experiment 3, the PT was determined in the subcutaneous tissue, but no significant effects of saline infusion were found. The present placebo-controlled experiments failed to show muscular or subcutaneous hyperalgesia after saline-induced muscle pain per se.     

Egg-size variation and reproductive success in the Herring Gull Lams argentatus: adaptive or constrained size of the last egg?

Herring Gull Larus argentatus eggs from a study colony in the Baltic showed a slight but significant variation in egg size within the laying sequence. Last-laid eggs were only about 5% smaller by volume than first eggs. There was no significant difference in dry yolk weight or dry albumen weight, although possible differences were evident. The chicks had nearly equal hatching weights and equally long tarsi. There was no differential mortality in the third chick in the study colony, and there were no indications of egg-size-mediated mortality. The birds in the colony produced an average of 1.45 fledglings per pair. Compared with several other studied colonies, the difference in egg size within a clutch was low, and a comparison of colonies from northwestern Europe suggests that variance within the clutch is negatively correlated with fledging success, so that a large difference in size between first and last eggs is associated with low fledging success. We suggest that the size of the last egg in the clutch reflects the feeding potential in the environment and is mainly a nonadaptive response to poor feeding conditions during laying.     

Algal species composition and phosphorus recycling at contrasting grazing pressure: an experimental study in sub-Antarctic lakes with two trophic levels

1. To test the response of algal communities to altered grazer abundance in lakes lacking efficient predators on herbivores, we performed field and experimental studies in two sub-Antarctic lakes (South Georgia).
2. The number of algal species in these high latitude lakes is low, and all dominant species have grazer-resistant adaptations, including spines in three dimensions ( Staurastrum sp.), large size ( Tribonema sp.), a mucus sheet allowing viable passage through the gut ( Chlamydocapsa sp., Elakatothrix sp.) or ability to recruit individuals from the sediment surface ( Mallomonas sp.).
3. Algal community composition was only slightly changed by experimentally altered grazer abundance, indicating that it was already adapted for a high grazing pressure. Hence, the diets of herbivores were restricted to vulnerable food organisms such as Mallomonas sp. and heterotrophic flagellates in the water column, and to benthic food sources.
4. At high grazer abundance, the concentration of available phosphorus (PO₄-P) in the water was lower than at low grazer abundances, due to inefficient nutrient regeneration by the copepod herbivores. Hence, in lakes where copepods are dominant grazers, algae suffer both directly from grazing and indirectly from reduced nutrient availability.     

The Transpiration Rate of Unhardened, Hardened, and Dehardened Seedlings of Spruce and Pine

Tissue injuries in winter are sometimes interpreted as caused by drought damages. The possibility that the tolerance of conifers of winter and spring conditions is increased through decrease in transpiration rate has been little investigated. The transpiration rate of 3 or 6 months old unhardened, hardened, and dehardened seedlings of Pinns silvestris L. and Picea abies (L.) Karst. was assessed gravimetrically, at 20°C. The transpiration rates of seedlings of spruce and pine which had been hardened for 3 months were about ¹/₂ the rates of dehardened seedlings. Transpiration during a dehardening period increased at different rates in pine and spruce. After a dehardening period of 3–5 days the transpiration rate of spruce reached a maximum, whereas pine reached the maximum transpiration rate after a dehardening period of 10–14 days. Transpiration of seedlings of spruce and pine hardened for 3 months showed only a very slight reaction to light and darkness. This indicated that stomata of hardened seedlings remained closed. The results are discussed in connection with frost and drought injuries in pine and spruce during early spring.