Tord Magnusson

Short‐term dynamics of abiotic and biotic soil 13CO2 effluxes after in situ 13CO2 pulse labelling of a boreal pine forest

Physical diffusion of isotopic tracers into and out of soil pores causes considerable uncertainty for the timing and magnitude of plant belowground allocation in pulse-labelling experiments. Here, we partitioned soil CO(2) isotopic fluxes into abiotic tracer flux (physical return), heterotrophic flux, and autotrophic flux contributions following (13)CO(2) labelling of a Swedish Pinus sylvestris forest. Soil CO(2) efflux and its isotopic composition from a combination of deep and surface soil collars was monitored using a field-deployed mass spectrometer. Additionally, (13)CO(2) within the soil profile was monitored. Physical (abiotic) efflux of (13)CO(2) from soil pore spaces was found to be significant for up to 48 h after pulse labelling, and equalled the amount of biotic label flux over 6 d. Measured and modelled changes in (13)CO(2) concentration throughout the soil profile corroborated these results. Tracer return via soil CO(2) efflux correlated significantly with the proximity of collars to trees, while daily amplitudes of total flux (including heterotrophic and autotrophic sources) showed surprising time shifts compared with heterotrophic fluxes. The results show for the first time the significance of the confounding influence of physical isotopic CO(2)-tracer return from the soil matrix, calling for the inclusion of meaningful control treatments in future pulse-chase experiments.

Carbon dioxide and methane formation in forest mineral and peat soils during aerobic and anaerobic incubations

Abstract Mineral and peat forest soils, sampled at three depths, were incubated aerobically and anaerobically at 16°C for 26 wk and were monitored for CH4 and CO2 formation. Mean CO2 production rates were similar under aerobic and anaerobic conditions in mineral subsoils with very low organic matter content, whereas in organic soils the rate was about 10 times greater under aerobic than anaerobic conditions. The correlations coefficient (r) between mean aerobic and mean anaerobic production rates was 0.98, for the entire data set. Mineral and organic samples incubated anaerobically both showed a decline in CO2 production rate with increasing time of incubation. The decline was more strongly related to incubation time than to the absolute concentrations of CO2 in the vials. The rates after 19 wk were approx. 10% of the initial rates. This inhibition was largely offset by flushing the vials with N2 gas, indicating the volatile nature of the inhibiting substances. Although CO2 production rates increased immediately upon flushing, there were still weak indications of a residual inhibiting effect. That, together with the rapid return of inhibition, suggested that non-volatile substances were also involved. One implication of these results is that the activity in anaerobic field soils very much depends on the removal of the inhibiting agents, e.g. by aeration during periodic draining of soil layers and by the movement of water through the soil. Methane formation occurred in most mor layers and peats. A well humified wood-Cyperaceae peat was, however, a notable exception. Methane production rates increased during the experimental period. The increasing CH4 production rates, and the final (26 wk) measured rates, were approximately proportional to the frequency of anaerobic conditions in the original field situation.

A method for equilibration chamber sampling and gas chromatographic analysis of the soil atmosphere

The method includes sampling of gases from an equilibration chamber permanently installed in the soil, transferring the sample to laboratory and subsequent measurement by gas chromatography.The equilibration chamber allows sampling of the gas phase both above and below the groundwater level, which is a major advantage. After significant concentration changes in non-saturated soils, gases in chambers regain equilibrium with the surrounding soils within 1–2 days. In the most unfavourable equilibration situations,i.e. in mineral subsoils with stagnant groundwater and very low biological activity, 90% equilibrium is attained in about 15 days.N2, O2+Ar, CO2, CH4, N2O, H2 and Ne, are measured on a series/bypass multi-column system, followed by a thermal conductivity detector.

Studies of the soil atmosphere and related physical characteristics in peat forest soils

Abstract The soil atmosphere in forested peat soils with depths of 0.8–1.2 m was monitored regularly for 3 years. Samples from gas equilibration chambers were analysed for N2, O2, CO4, CH4, N2O and Ne by gas chromatography. Short spring periods with simultaneous and rapid O2 decrease/CO2 increase were the characteristic features at a soil depth of 5 cm. They were the effects of perched water tables on frozen soil layers. The soil atmosphere composition at a depth of 20 cm was particularly variable in the poorly drained sites, where this soil depth was close to the alternating level of the groundwater. At a depth of 50 cm, CO2 and CH4 had minimum concentrations in early or mid-summer and maximum concentrations in the late autumn or early winter. The reverse pattern for O2 was indicated, but was less clear. In individual profiles and on average, O2 decreased and CO2 increased with increasing depth, except during some transient periods in the spring. Medium (H6) humified, inadequately drained Sphagnum peat differed from well humified (H8), well-drained wood peat, in that it contained considerable concentrations of CH4. Only very small concentrations were occasionally found in the humified wood peat and they did not increase when the groundwater level rose after clearfelling. The groundwater level rose after clearfelling on both types of peat. Concentrations of O2 decreased and CO2 increased in the topsoil, particularly in the medium humified and insufficiently drained Sphagnum peat. The soil atmospheres, as represented by mean concentrations and extreme concentrations at three depths during the growing season, were significantly different on all plots, including the parallel clearfelled and forested plots.

Long-term effects of stump harvest on mercury and general chemistry in discharge water

ABSTRACT This synoptic study evaluates water chemistry in stump-harvested and conventionally logged reference areas, located in South-Central Sweden, 20–30 years after harvest and reforestation. Electrical conductivity, pH, alkalinity (), nitrate nitrogen () and total organic carbon (TOC) were measured in discharging groundwaters and in low-order streams and ditches. The groundwaters were further analysed for total mercury (THg) and methyl mercury (MeHg). Additionally, solid phase Hgtot and MeHg were measured in stream mudbottoms. The mean MeHg concentration and mean MeHg/TOC ratio were significantly (p < .05) higher in discharging groundwater from stump-harvested compared to reference areas. In contrast, the concentration of THg did not differ. Likewise, there were no significant treatment differences for electrical conductivity, pH, or TOC. In the stream-/ditchwaters also no significant differences were found, but electrical conductivity (p = 0.07) and pH (p = .08) tended to be lower in stump-harvested areas. Hgtot and MeHg concentrations in stream-/ditch sediments did not differ between treatments. These results suggest that weakly enhanced MeHg concentrations may be present in the riparian groundwater zone 20–30 years after stump harvest.

Relationships between soil properties and the soil atmosphere in Swedish forest soils

Concentrations of O2 and CO2 in 11 mineral and peat forest soils were related to physical, chemical and biological site variables by means of PLS modelling. Soil depth, volumetric water content, air‐filled porosity, soil temperature and soil respiration explained 66% of the spatial variation in gas concentrations, when all soils and depths were included. With the inclusion of complementary X variables, the model explained 76% of the Y variance. The X variables affecting gas transport in the soil explained more of both spatial and temporal gas variations than those affecting the biological activity. Much of the effect of water content originated in the early growing season and were conditioned by frozen soil layers, hampering the infiltration of water from snowmelt. Soil moisture, rather than temperature, thus regulates the apparent soil atmosphere variations in these forest soils of northern Sweden, where a temperate climate with cold and snowy winters and moist summer conditions prevails.

Ash as a phosphorus fertilizer to reed canary grass: effects of nutrient and heavy metal composition on plant and soil

Fertilization effects and risks of heavy metal enrichment were studied in a field experiment, in which plots of reed canary grass (RCG) were treated annually with three different fertilizers: Ash from co‐combustion of RCG and municipal wastes (mixed ash), pure RCG ash, and commercial fertilizer (control). RCG ash is a waste product that is currently expensive to dispose of. The amounts of nutrients applied annually were 100 kg ha−1 N, 15 kg ha−1 P, and 80 kg ha−1 K in all treatments. In the ash treatments, all P derived from ash, whereas N and part of the K were supplemented by fertilizers. The amount of heavy metals exceeded the limits set by the Swedish Environmental Protection Agency for all elements analyzed in the mixed ash and for Ni and Cr in the RCG ash. There were no significant differences between treatments in terms of RCG dry matter yield obtained at harvest in spring, or in heavy metal concentrations in the biomass.

Swedish forest research and higher education ‐ challenging issues and future strategies of forest research and education in Sweden

This paper gives an overview of current forest education in Sweden and its historical development. In Sweden, education and research is dominated by one actor, the Faculty of Forest Sciences at the Swedish University of Agricultural Sciences (SLU). In this paper, we discuss the values of a solid academic base, a close cooperation between research and development, and the best balance between theory and practise. We conclude that the overall challenge for Swedish Forest education, and indeed for comparable natural sciences programmes in other countries, is to widen the scope to include more social and humanistic aspects of forests and forestry. Management of “multifunctional forestry” best describes the vision we aim at. The change in syllabus, compared to current education, must of course differ among countries due to different forest and land use history and conditions. We wish to emphasize that in case of Sweden, a country where production forests are the economically most important natural resource, this recommendation is not a general shift of focus away from forest production. We do mean however, that the academics working in forestry must be equipped with sufficient knowledge about environmental issues and other functions of forests to be able to cope with future demands. We also wish to emphasise the international perspective of forestry. At the individual level students should be provided possibilities to take full master degrees (majors) in other subjects than Forest Management (e.g. Biology, Soil Science, Economics). We believe that there are some important requirements to keep higher education in Forest Sciences competitive and successful in the long term: a solid academic/ scientific base; a close association between research and teaching; and a mix of theory and practise/field studies. Forestry studies should be challenging to the students and provide them possibilities for personal development that enables them to meet unknown demands in the future.