Gunnar Ekbohm

Nitrogen level and decomposition in Scots pine needle litter

The decomposition of Scots pine green needles and brown needle litter was followed. The nitrogen level was initially 1.2% in green and 0.40% in brown needles. The decomposition rate of the nitrogen-rich litter was initially higher than for the nutrient-poor but after three years the accumulated weight loss was similar in both cases. It was found that the decomposition rate of the lignin of the nitrogen-rich litter was significantly lower than that of the nitrogen-poor in the incubation period after 500 d.

Reduction of decomposition rates of Scots pine needle litter due to heavy-metal pollution

Decomposition of unpolluted Scots pine needle litter was studied in two heavy-metal-pollution gradients in Sweden; one near a brass mill and the other around a primary smelter. In the latter area locally collected polluted Scots pine needle litter was also incubated. Decomposition rates were strongly influenced by the metal pollution and a decrease in the rate of mass-loss occurred. In the brass-mill gradient this occurred until about 1 km from the pollution source which corresponded to about 500 µg Cu and 1 000 µg Zn g−1 soil. Data are presented to indicate that lignin decomposition was more sensitive to pollution than decomposition of whole litter and affected further away from the pollution sources. At the smelter sites, the metal-polluted needle litter decomposed more slowly than the unpolluted needle litter, and this difference was enhanced close to the smelter. The results indicate that heavy metals accumulated in needles prior to shedding have a long-term impact on the subsequent decomposition of the litter. Both litter quality and soil factors thus contribute to the reduced litter decomposition rate in metal-polluted forests. A new non-linear model with decreasing decay rate was used in the statistical evaluation. The model can be used to characterize the effects of pollution on decomposition rate.

Nosema Apis, Sampling Techniques and Honey Yield

SummaryEstimates of levels of Nosema apis infection in honeybee colonies by three different sampling and examination combinations were correlated with honey yield. Samples of 60 bees were taken in early spring in Uppsala, Sweden, live bees being taken from the cluster and dead ones from the bottom board. Parallel samples of hive bees were examined individually and compositely. Dead bees were only examined compositely. The mean spore count/bee of each composite sample was estimated with a hemacytometer. The correlation of honey yield with Nosema level was much larger for samples of live bees irrespective of counting methods, than for composite samples of dead bees. The closest correlation with honey yield (-0·707) was found for number of honeybees infected. It is concluded that when colonies are being examined in spring to determine the effects of Nosema on honey yield, it is best to sample live bees and not dead ones and to examine the bees of the samples individually rather than compositely.

Decomposition of litter and soil organic matter—can we distinguish a mechanism for soil organic matter buildup?

This synthesis paper presents a model for estimating the buildup of soil organic matter in various types of coniferous forests. The knowledge used was obtained from a well‐studied forest with good Iitterfall data, decomposition information and validation measurements of the soil organic matter layer. By constructing a simple model for litterfall, and the information on maximum decomposition levels for litter, we could estimate the annual increase in soil organic matter and extend this to encompass stand age. The validation measurement and the estimated amount of soil organic matter differed by about 8 or 26% over a 120‐yr period, depending on the litterfall model. The estimated increased storage of soil organic matter as a consequence of climate change was found to be drastic. We thus found that the soil organic matter layer would grow about four times as fast as a result of the needle component only. This estimate was based on a comparison between latitudes with a difference of 17°.

Decomposing needle litter in Pinus contorta (lodgepole pine) and Pinus sylvestris (scots pine) monocultural systems — is there a maximum mass loss?

By extrapolation of measured mass‐loss values, maximum values for accumulated litter‐mass loss were estimated by using a nonlinear statistical model. This model predicted that the proportion of mass lost through decomposition should be on the average about 85% for Scots pine needle litter and for lodgepole pine needles the corresponding value was almost 100%. The single incubations of Scots pine and lodgepole pine needle litter were made simultaneously and in parallel plots and could thus be compared pairwise. When thus compared, the limit values (asymptotic values) were significantly different in five cases out of six—the exception being a short measurement series. Lodgepole pine is an introduced species in this system.

Decomposition of heterogeneous substrates; an experimental investigation of a hypothesis on substrate and microbial properties

Abstract The production-to-assimilation ratio (microbial efficiency) of a microorganism feeding on a substrate depends both on the organism and the substrate. An experiment was set up to investigate whether the microbial efficiency can be defined as the product of a microbial property (an efficiency factor) and a substrate property (substrate quality). By following changes in carbon and organic nitrogen content of birch, aspen and spruce wood, which were degraded by either the brown-rot fungus Poria oleracea or the white-rot fungus Phanernchaete chrysosporium over a 130 day period, we showed that this seems to be the case. It was also found that the substrate quality decreased in the order birch > aspen > spruce. which corresponded to increasing lignin concentrations. However, aspen and spruce appeared much closer in quality than birch and aspen although the latter two are much closer in lignin concentrations. For any given substrate P. oleracea had a microbial elliciency which was ca 50% higher than that of Ph. rhrysosporium. In addition, the experiment showed that when both nitrate and ammonium were available as N sources Ph. chrysosporium preferentially used nitrate whereas P. oleracea started using nitrate only when all ammonium in the growth medium had been exhausted.