Göran Bengtsson

Gross nitrogen mineralization-, immobilization-, and nitrification rates as a function of soil C/N ratio and microbial activity

A laboratory experiment was designed to challenge the idea that the ON ratio of forest soils may control gross N immobilization, mineralization, and nitrification rates. Soils were collected from three deciduous forests sites varying in C/N ratio between 15 and 27. They were air-dried and rewetted to induce a burst of microbial activity. The N transformation rates were calculated from an isotope dilution and enrichment procedure, in which (NH4Cl)-N-15 or (NaNO3)-N-15 was repeatedly added to the soils during 7 days of incubation. The experiments suggested that differences in gross nitrogen immobilization and mineralization rates between the soils were more related to the respiration rate and ATP content than to the C/N ratio. Peaks of respiration and ATP content were followed by high rates of mineralization and immobilization, with 1-2 days of delay. The gross immobilization of NH4+ was dependent on the gross mineralization and one to two orders of magnitude larger than the gross NO3- immobilization. The gross nitrification rates were negatively related to the ATP content and the C/N ratio and greatly exceeding the net nitrification rates. Taken together, the observations suggest that leaching of nitrate from forest soils may be largely dependent on the density and activity of the microbial community.

Effects of metal pollution on the earthwormdendrobaena rubida (Sav.) in acidified soils

AbstractSurvival of adultDendrobaena rubida, cocoon production, cocoon viability, and growth of juveniles were examined in laboratory experiments when the worms were reared in acidified and metal polluted soils. Solutions of Cu, Cd and Pb were added to give total concentrations of 10, 100 and 500 μg g−1 in soils with a pH of 4.5, 5.5 and 6.5. Adult tissues, hatchlings and cocoons were analyzed for metals. D. rubida survived poorly in soils with low pH, especially in combination with Pb or Cu, which accumulated in seminal vesicles and cerebral ganglion. Cocoon production was halved when pH was lowered from 6.5 to 4.5 and metals reduced the cocoon number even more in the most acid soils. Hatching success was lower than 20 % in acidified soils. In contrast, the number of hatchlings increased when pH decreased and peaked in soils polluted with Cd. While low pH reduced the embryonic development time, metals prolonged it. Juveniles grew slowly and died early at low pH.

Critical metal concentrations for forest soil invertebrates

Based on a review of the literature on metal effects on forest soil invertebrates 100 to 200 mg Pb, < 100 mg Cu, < 500 mg Zn and 10 to 50 mg Cd kg−1 soil or litter are suggested as maximum allowable metal concentrations that will cause no adverse effects. These critical levels, emphasizing effects on abundance, diversity and life history parameters, are considered conservative and tentative, since few of the surveys they rely on were designed for critical level assessment; especially with respect to long-term consequences on decomposition and nutrient regeneration. The variation between animal species and individuals in susceptibility to metals due to differences in uptake, storage and tolerance are addressed.

Population density and tissue metal concentration of lumbricids in forest soils near a brass mill

Abstract The effect of metal pollution on species composition, population density, and age structure of earthworms was studied in coniferous forests near a brass mill in SE Sweden. Samples were taken in two biotapes, dominated by Deschampsia flexuosa and Vaccinium myrtillus, respectively, from eight sites at varying distances (175–20 000 m) from the mill. pH and CEC were found to increase in the soil close to the mill. A decrease in the concentration of extractable metals (Zn, Cu, Pb) could be followed up to 1·2 km from the emission source. Copper and lead were analysed in pharynx, gizzard, muscles, clitellum, seminal vesicles and cerebral ganglion of different earthworm species. Generally, the concentration of copper in tissues was higher compared with lead and inversely proportional to the distance from the mill. A substantial metal uptake was found in the vital tissues, such as seminal vesicles and cerebral ganglion. Juveniles tended to have higher metal concentrations compared with adults. Density and biomass of earthworms was proportional to the distance from the mill, especially in the Deschampsia-dominated biotopes. Dendrobaena octaedra was the most abundant lumbricid species but was absent in soils within 1 km from the mill. Data indicate that the reduced density of earthworms near the mill was due to metal toxicity, but food deprivation could not be ruled out as a possible factor. Reasons for decreased density of earthworms at more remote sites are discussed and data on density and soil zinc concentrations are used to predict the density of earthworms at a metal polluted site.

Food- and density-dependent dispersal: evidence from a soil collembolan

1. Dispersal in a fungivore species of Collembola, Onychiurus armatus, in a homo- geneous soil was theoretically approached as a deterministic compartmental process, in which the movement of animals between discrete patches could be described by a series of differential equations or by the discrete geometric probability distribution, assuming a constant probability to move from one patch to the next. 2. Experiments were designed for a release of collembolans in two types of soil in a physical arrangement of distinct patches represented by vials connected by tubings to cover a distance of 40 cm. Dispersal distances of individuals were determined, and theoretical and observed distributions compared. 3. Dispersal rates, estimated from transfer rate constants, ranged from 0 020 to 1 42 day-1, suggesting that an average 0. armatus moved less than 10 cm day -1. The probability to leave a patch varied between 0 10 and 0 50. 4. Dispersal was dependent on population density, soil type and length of fungal mycelium; it was almost twice as high at a high than at a low density (90 000 and 30000 individuals m-2) in a mor soil and four times as high in a sandy compared with a mor soil. Dispersal rate decreased as the mycelial length increased, especially in a sandy soil. 5. Collembolans in a feeding phase had a higher tendency to disperse than those that were moulting. 6. Enriching the soil patch at 40 cm distance from the release point with a favoured food item, the fungal species Mortierella isabellina, increased dispersal rate by more than four times in a mor soil, suggesting that fungal odour can attract collembolans from a large distance and enhance their rate of movement more than a three-fold increase of their population density does. (Less)

Evolutionary response of earthworms to long-term metal exposure

The occurrence of a number of soil intertebrate species in severely polluted soils raises the question whether they have evolved resistance, e.g. by adaptation or acclimatization. This was examined in experiments on the earthworm Dendrobaena octaedra (Sav.) using specimens from sites polluted by a brass industry. One site, exposed since the 17th century, was situated close to an old mill, another was near a modern mill that has been operating for the last two decades, and the third was a non-polluted reference site. Adults and juveniles of D. octaedra from each site were reared in each of the three different soils. Growth (increase of body weight), survival, and cocoon production of the populations were followed over 225 d

Relative abundance and resistance traits of two Collembola species under metal stress

Population differentiation was studied in Onychiurus armatus (Tullb.) and Isotoma notabilis Schaffer from a reference site and two highly polluted (Cu, Zn) sites (long-term and short-term exposed, respectively) in the Gusum area, SE Sweden. Growth, survival and reproduction were followed in a F1 generation of O. armatus reared on a diet of the fungus Verticillium bullosum (W. Gams and Malla) grown on a series of Cu+Zn amended agar plates. Survival and reproduction were observed in a P generation of I. notabilis incubated in soils with enhanced concentrations of Cu and Zn. Metals affected growth rate but not mean maximum length of O. armatatus. The growth rates of both populations decreased significantly with increasing metal concentration

Fungal odour attracts soil Collembola

Abstract A soil-inhabiting species of Collembola, Onychiurs armatus (Tullb.), locates its food source, hyphomycetous fungi, by volatile compounds released from the mycelium. Attractivity was ranked based on the odour of the fungal species, represented by compounds in the range C 5 -C 18 and typically released in olfactometer experiments at a rate of 250 pg h −1 from a 175 mm 2 fungal patch representing about 400 μg mycelium. Among fungi grown in agar Verticillium bulbillosum was most attractive; the preference of O. armatus switched to other species, however, when these were cultured in soil.

Growth Changes Caused by Metal Uptake in a Population of Onychiurus armatus (Collembola) Feeding on Metal Polluted Fungi

The effects of uptake of copper and lead on the growth of Onychiurus armatus (Tullb.) (Collembola) were studied in laboratory experiments. Specimens were reared in petri dishes, supplied with a soil borne fungus Verticillium bulbillosum, (W. Gams and Malla), which was grown on a substrate contaminated with different amounts of metals. Growth of specimens of 0. armatus was measured in the F1 and F2 generations. Growth data were fitted to a growth model and the best estimates of growth rate and average maximum length were calculated and compared for different metal contaminations. The fungus accumulated metals efficiently, reaching levels of 1000 to 3500 ppm on substrates containing 15 to 300 ppm metals. 0. armatus concentrated metals during the first two weeks of its life cycle, and then excreted metals towards a steady state level. Copper concentration in the body was higher than lead concentration, and the metals behaved antagonistically when mixed. Neither metal was accumulated by Collembola, and equilibrium concentrations of copper varied from 150 to 600 ppm. Growth rate and average maximum lengths were higher at a moderate metal pollution, both in F1 and F2, and significantly reduced on substrate containing 90 ppm metal or more. The lowest concentration of copper and lead in specimens with significantly reduced growth rate was about 200 ppm. This concentration was also found in a field population in the vicinity of a brass mill. The consequences of reduced growth rate on survival and reproduction in a population are discussed.

Selective odor perception in the soil collembolaOnychiurus armatus.

The olfactorial response of the fungivorous soil collembolanOnychiurus armatus was examined in a bioassay covering volatile compounds identified in the odor blends of two of its preferred fungal speciesMonierella isabellina andVerticillium bulbillosum. The odor of the fungi was trapped using activated carbon filters, extracted with diethyl ether, and subjected to GC-MS analysis. About 50% of the compounds resolved by GC were identified by a combination of electron impact and chemical ionization mass spectrometry. In a Y-shaped olfactometer the collembolans were attracted to a variety of common odors, such as CO2 and 2-methyl-1-propanol, and a species-specific odor, such as 1-heptene, and arrested by, for example, decanal and 2-octene. The response was not improved by pairwise combinations of common and specific odors. An amount of 0.5 ng of ethyl acetate or 3 pg of 1-pentanol was sufficient to attract the collembolans. The specific compounds ofV. bulbillosum, 1-heptene and 1-octen-3-ol, may be key stimuli explaining whyO. armatus prefersV. bulbillosum.