CO2 exchange in an organic field growing barley or grass in eastern Finland

The CO₂ dynamics were measured in an organic soil in eastern Finland during the growing season and wintertime, and the annual CO₂ balance was calculated for plots where barley or grass was grown. During the summer, the CO₂ dynamics were measured by transparent and opaque chambers using a portable infrared gas analyser for the CO₂ analyses. During the winter, the CO₂ release was measured by opaque chambers analysing the samples in the laboratory with a gas chromatograph. Statistical response functions for CO₂ dynamics were constructed to evaluate the annual CO₂ exchange from the climatic data. The net CO₂ exchange was calculated for every hour in the snow‐free season. The carbon balance varied extensively depending on the weather conditions, and type and phenology of vegetation. During the growing season, the grassland was a net source while the barley field was a net sink for CO₂. However, both soils were net sources for CO₂ when autumn, winter and spring were included also. The annual CO₂ emissions from the grassland and barley soil were 750 g CO₂‐C m^?2 and 400 g CO₂‐C m^?2, respectively. The carbon accumulated in root and shoot biomass during the growing season was 330 g m^?2 for grass and 520 g m^?2 for barley. The C in the aboveground plant biomass ranged from 43 to 47% of the carbon fixed in photosynthesis (P_G) and the proportion of C in the root biomass was 10% of the carbon fixed in photosynthesis. The bare soils had 10–60% higher net CO₂ emission than the vegetated soils. These results indicate that the carbon balance of organic soils is affected by the characteristics of the prevailing plant cover. The dry summer of 1997 may have limited the growth of grass in the late summer thus reducing photosynthesis, which could be one reason for the high CO₂ release from this grass field.     

Methane dynamics of a restored cut‐away peatland

We measured a cut‐away peatland's CH₄ dynamics using the static chamber technique one year before and two years after restoration (rewetting). The CH₄ emissions were related to variation in vegetation and abiotic factors using multiple linear regression. A statistical model for CH₄ flux with cottongrass cover (Eriophorum vaginatum L.), soil temperature, water level, and effective temperature sum index as driving variables explained most (r² = 0.81) of the temporal and spatial variability in the fluxes. In addition to the direct increasing effect of raised water level on CH₄ emissions, rewetting also promoted an increase of cottongrass cover which consequently increased carbon flux (substrate availability) into the system. The seasonal CH₄ dynamics in tussocks followed seasonal CO₂ dynamics till mid August but in late autumn CH₄ emissions increased while CO₂ influxes decreased. The reconstructed seasonal CH₄ exchange was clearly higher following the rewetting, although it was still lower than emissions from pristine mires in the same area. However, our simulation for closed cottongrass vegetation showed that CH₄ emissions from restored peatlands may remain at a lower level for a longer period of time even after sites have become fully vegetated and colonized by mire plants.     

Ergosterol Content in Various Fungal Species and Biocontaminated Building Materials

This paper reports the ergosterol content for microbial cultures of six filamentous fungi, three yeast species, and one actinomycete and the ergosterol levels in 40 samples of building materials (wood chip, gypsum board, and glass wool) contaminated by microorganisms. The samples were hydrolyzed in alkaline methanol, and sterols were silylated and analyzed by gas chromatography-mass spectrometry. The average ergosterol content varied widely among the fungal species over the range of 2.6 to 42 μg/ml of dry mass or 0.00011 to 17 pg/spore or cell. Ergosterol could not be detected in the actinomycete culture. The results for both the fungal cultures and building material samples supported the idea that the ergosterol content reflects the concentration of filamentous fungi but it underestimates the occurrence of yeast cells. The ergosterol content in building material samples ranged from 0.017 to 68 μg/g of dry mass of material. A good agreement between the ergosterol concentration and viable fungal concentrations was detected in the wood chip (r > 0.66, P ≤ 0.009) and gypsum board samples (r > 0.48, P ≤ 0.059), whereas no relationship between these factors was observed in the glass wool samples. For the pooled data of the building materials, the ergosterol content correlated significantly with the viable fungal levels (r > 0.63, P < 0.0001). In conclusion, the ergosterol concentration could be a suitable marker for estimation of fungal concentrations in contaminated building materials with certain reservations, including the underestimation of yeast concentrations.     

Effects of Histamine on Circadian Rhythms and Hibernation

Histamine appears to play a role in regulation of sleep and arousal as well as in synchronizing endogenous circadian rhythms with exogenous photic cues. Direct application of histamine to the suprachiasmatic nucleus (SCN), the site of the mammalian circadian pacemaker, phase shifts the circadian rhythm in neural activity. Intraventricular injections of histamine also phase shift circadian rhythms as do micro-injections directed towards the SCN. The magnitude and direction of the phase shifting effects of histamine depend on circadian phase in a manner similar to light. Depletion of brain histamine levels by inhibition of histamine synthesis reduces phase shifts to light. Histamine appears to influence phase shifts to light via a direct modulation of NMDA receptors in the SCN. Increased histamine levels and turnover observed in hibernating animals render it possible that histamine is a key regulator of hibernation. Thus histamine participates in an important link between sleep, circadian rhythms, and hibernation.     

Leptodora kindti and Flexible Foraging Behaviour of Fish – Factors behind the Delayed Biomass Peak of Cladocerans in Lake Hiidenvesi

In the eutrophic L. Hiidenvesi, the spring biomass maximum of cladoceran zooplankton is missing and the highest biomass takes place in July–August. The factors behind the delayed biomass peak were studied in four different basins of the lake with concomitant data on cladocerans assemblages, density of the predatory cladoceran Leptodora kindti and food composition of fish. In all the basins, the abundance of Leptodora peaked in June, being highest (up to 800 ind. m^–3) in the two most shallow basins (max depth < 4 m). The duration of the high population density was short and in July‐August Leptodora density stayed below 200 ind. m^–3, although the water temperature was still favourable. The collapse of the Leptodora population coincided with the change in the feeding habits of fish. In early summer, fish predation was targeted mainly on copepods and zoobenthos, while in high summer Leptodora was one of the main preys of perch, white bream and bleak. The biomass of herbivorous cladocerans was below 10 μg C l^–1 in June, and climbed to a maximum in August in the two most shallow basins (34 and 76 μg C l^–1), in July in the deepest basin (27 μg C l^–1), and in September in the intermediate basin (55 μg C l^–1). In the two most shallow basins, the death rate of the dominating cladoceran, Daphnia cristata, closely followed the food consumption rate by the Leptodora population. In the deeper basins, the agreement was not so close, smelts (Osmerus eperlanus) and chaoborids being important predators of herbivores. The duration of the period of high Leptodora density thus depended on the predation pressure by fish, while the increased fish predation on Leptodora in July–August allowed the elevation of the biomass of herbivorous cladocerans.     

Spatial and seasonal variation in greenhouse gas and nutrient dynamics and their interactions in the sediments of a boreal eutrophic lake

Dynamics of greenhouse gases, CH₄, CO₂ and N₂O, and nutrients, NO ₂ ^– + NO ₃ ^– , NH ₄ ⁺ and P, were studied in the sediments of the eutrophic, boreal Lake Kevätön in Finland. Undisturbed sediment cores taken in the summer, autumn and winter from the deep and shallow profundal and from the littoral were incubated in laboratory microcosms under aerobic and anaerobic water flow conditions. An increase in the availability of oxygen in water overlying the sediments reduced the release of CH₄, NH ₄ ⁺ and P, increased the flux of N₂O and NO ₂ ^– + NO ₃ ^– , but did not affect CO₂ production. The littoral sediments produced CO₂ and CH₄ at high rates, but released only negligible amounts of nutrients. The deep profundal sediments, with highest carbon content, possessed the greatest release rates of CO₂, CH₄, NH ₄ ⁺ and P. The higher fluxes of these gases in summer and autumn than in winter were probably due to the supply of fresh organic matter from primary production. From the shallow profundal sediments fluxes of CH₄, NH₄ ⁺ and P were low, but, in contrast, production of N₂O was the highest among the different sampling sites. Due to the large areal extension, the littoral and shallow profundal zones had the greatest importance in the overall gas and nutrient budgets in the lake. Methane emissions, especially the ebullition of CH₄ (up to 84% of the total flux), were closely related to the sediment P and NH ₄ ⁺ release. The high production and ebullition of CH₄, enhances the internal loading of nutrients, lake eutrophication status and the impact of boreal lakes to trophospheric gas budgets.     

The Microbial Community Structure of Drinking Water Biofilms Can Be Affected by Phosphorus Availability

Microbial communities in biofilms grown for 4 and 11 weeks under the flow of drinking water supplemented with 0, 1, 2, and 5 μg of phosphorus liter⁻¹ and in drinking and warm waters were compared by using phospholipid fatty acids (PLFAs) and lipopolysaccharide 3-hydroxy fatty acids (LPS 3-OH-FAs). Phosphate increased the proportion of PLFAs 16:1ω7c and 18:1ω7c and affected LPS 3-OH-FAs after 11 weeks of growth, indicating an increase in gram-negative bacteria and changes in their community structure. Differences in community structures between biofilms and drinking and warm waters can be assumed from PLFAs and LPS 3-OH-FAs, concomitantly with adaptive changes in fatty acid chain length, cyclization, and unsaturation.     

Scale and seasonal sex-ratio trends in northern goshawk Accipiter gentilis broods

In many populations of size dimorphic birds, brood sex ratios change with advancing laying date. The slopes of these trends, however, vary in time and space, both between and within species. We studied brood sex ratios (proportion of males) of northern goshawks Accipiter gentilis in Finland in relation to laying date using ringing data from 1989 to 1998. At the nationwide scale, i.e. the whole of Finland, between-year variation in offspring sex ratio was moderate, and the sex ratio did not change with later laying date. At a regional scale, the sex ratio was seasonally constant in one region but decreased in another, although the laying-date/brood-size relationship was identical. Hence, the size and sex composition of goshawk broods are locally two uncoupled facets of reproduction. Both the national and regional patterns differ drastically from the pattern of a Dutch population, where sex ratio increased seasonally. We suggest that spatial variation in inter-annual seasonal sex-ratio trends might be indicative of the scale at which sex-ratio feedback functions. The sex ratio of breeders is a factor that could add to the understanding of the observed geographical differences in seasonal sex-ratio patterns.