Veikko Huhta

Effects of earthworms on decomposition processes in raw humus forest soil : a microcosm study

SummaryThe earthworms Lumbricus rubellus (Hoffmeister) and Dendrobaena octaedra (Savigny) were studied in the laboratory to determine their effects on decomposition and nutrient cycling in coniferous forest soil. CO2 evolution was monitored, and pH, PO43−−P, NH4+−N, NO3−−N, total N, and total C in the leaching waters were measured. After three destructive samplings, numbers of animals, mass loss, pH, and KCl-extractable nutrients were analysed.The earthworms clearly enhanced the mass loss of the substrate, especially that of litter. L. rubellus stimulated microbial respiration by 15–18%, whereas D. octaedra stimulated it only slightly. The worms significantly raised the pH of the leaching waters and the humus; L. rubellus raised the value by 0.2–0.6 pH units and D. octaedra by 0.1–0.4 units. Both worms increased N mineralization. Although the biomass of both worms decreased during the experiment, the N released from decomposing tissues did not explain the increase in N leached in the presence of earthworms. The worms influenced the level of PO43−−P only slightly.

Dispersal of microarthropods in forest soil

Summary This experiment was a part of a research on the soil community in anthropogenous birch stands in Finland. In that study it was found that communities of Collembola are similar in birch stands of different origin (cultivated field or spruce forest), while the communities of Oribatida are essentially different. When compared to original spruce forest, the communities of both groups are different. Cultivation eliminates the populations of most microarthropod species, that have to disperse after reforestation from the surrounding areas. The aim of the experiment was to study the ambulatory dispersal of soil microarthropods. It was carried out in plastic boxes filled with an intact block of defaunated surface soil taken from a birch stand that was established ca. 30 years earlier on a cultivated field. A strip of intact spruce forest soil was placed at one end of the boxes to harbour the source populations. At the opposite end we placed a row of pitfall traps. Soil samples were taken every two weeks at increasing distances from the source soil using a metal corer, and animals were extracted in a high gradient apparatus. The pitfalls were also emptied every two weeks. The experiment lasted for ten weeks. Pitfall and soil sample data gave an estimation of the maximum dispersal rate for each species or genus. The distance that the populations could potentially disperse in 30 years (age of the stand) indicated that some, but not all of the species could have actively migrated to the central parts of the birch stand (30 m).

Habitat patchiness affects decomposition and faunal diversity: a microcosm experiment on forest floor

Abstract Environmental heterogeneity has been intensively studied, but little is known about relationships between habitat patchiness and soil processes. The aim of this study was to investigate (1) the impact of patchiness of the litter layer on the decomposer community and litter decomposition rate, and (2) whether the impact of soil fauna on the rates of processes differs in relation to patchiness. An experiment was carried out in microcosms with coniferous forest humus and four kinds of litter with different C:N ratios or stages of decomposition, either separately (i.e. in patches) or mixed with each other. Microarthropod species diversity was better maintained in the patchy systems. In the absence of soil fauna, community respiration was higher in the patchy microcosms, but in the presence of fauna the opposite pattern was observed. The contribution of soil fauna to the rate of decomposition was clearly greater in the mixed litter systems. Based on the results, a hypothesis is presented that in the patchy litter layer the soil fungi can create connections between different materials located some centimeters apart, thus enhancing decomposition, while in the mixed litter the scale of millimeters is more appropriate for the soil fauna, known to accelerate the process rates.

Capacity of various organic residues to support adequate earthworm biomass for vermicomposting

SummaryWe tested the potential of different kinds and combinations of wastes to support the biomass ofEisenia fetida (Sav.) capable of processing a given amount of waste in a period of ca. 1 month. Mixed miscellaneous wastes and activated sewage sludge mixed with or embedded in sieved pine bark showed capacity to maintain the required biomass for a long period. Wastes were converted into odourless castings of good physical structure, provided that a sufficient population was present from the beginning and fresh waste was added regularly. A horizontally working “worm bed compost” was designed instead of the “load-on-top” principle.

Evaluation of Different Similarity Indices as Measures of Succession in Arthropod Communities of the Forest Floor After Clear-Cutting

SummaryCommunities of spiders (Araneae) and beetles (Coleoptera) living in the soil and litter of clear-cut areas were compared with those of intact forest stands. Sixteen different indices of similarity were tested on three sets of material: spiders and beetles examined during one year in three clear-cut areas felled 3, 6 and 9 years earlier, and spiders in one clear-cut area examined during 7 successive years after felling. Other sources of evidence showed that succession in the spider community was divergent for at least 7 years after felling.The indices that seemed to express the changes best were: (1) Kendalls rank correlation test, (2) the Bray-Curtis measure, (3) Renkonens percentage similarity, (4) the correlation coefficient r (2 to 4 after logarithmic transformation of data), (5) the Canberra metric, and (6) the diversity overlap (R0). The properties of the indices are discussed.

Growth increase of birch seedlings under the influence of earthworms. A laboratory study

The effects of the earthworm Lumbricus rubellus (Hoffm.) on net production and nitrogen content of birch seedlings were studied in laboratory microcosms. Coniferous forest floors with litter, humus and mineral horizons were simulated in transparent plastic cylinders. The materials were partially sterilized by microwaving, and re-inoculated with microflora and -fauna. A young (9 cm) birch seedling (Betula pendula Roth) was planted in each container. Earthworms were added to half of the replicates. The microcosms, through which a constant air flow was maintained, were incubated in a climate chamber. After two growth periods, leaf and stem biomasses of birch in treatments with earthworms increased by 33 and 24%, respectively, compared with controls, while the root biomass was slightly lower. The N contents of leaves were almost twice as high in the earthworm treatments as in the controls. The nitrogen contributed by dead earthworm biomass could only partly explain this difference. The plants absorbed virtually all net mineralized nitrogen and phosphorus from the soil.

Biological changes in northern spruce forest soil after clear-cutting

Abstract In northern Finland, reforestation has frequently failed in clear-cut areas of coniferous forests. These failures prompted an investigation of the changes in the invertebrate fauna and in the bacterial populations of such forest soils after clear-cutting. Clear-cut areas in four neighbouring sites of various ages were sampled monthly, and the results were compared with those for samples taken simultaneously from a control site in an untreated spruce stand. After clear-cutting, the total biomass of the invertebrate fauna showed a strong increase, mainly due to an increase of the Enchytraeidae populations. The biomass reached its maximum after 7 yr and returned to the original level by year 13 after clear-cutting. Bacterial counts showed the same pattern as the faunal biomass; the numbers at first increased after clear-cutting, then regressed, and approached the control value after 13 yr. Cellulose degradation and soil respiration behaved in the same way. Bacterial numbers showed a significant seasonal variation at all sites, including the control; counts were maximal after the snow melt in June and decreased during the growing season.

Polychlorinated phenols and their metabolites in soil and earthworms of sawmill environment

Abstract Topsoil and earthworm samples collected from three Finnish sawmill environments were analysed for polychlorinated phenols, 2,3,4,6-tetrachloro- and pentachlorophenol, and their metabolites. Analyses were carried out by gas chromatography/mass spectrometry using a selected ion monitoring technique and by dual-channel gas chromatography using quartz capillary columns and two electron capture detectors. The total chlorophenol concentrations ranged from ca. 260 to 480 μg/g (dry weight) in soil and from ca. 140 to 3500 μg/g fat in earthworms. The most important metabolites in soil were chlorinated dihydroxy-benzenes (also at ppm level); only traces of chlorinated anisoles were detected in soil. 2,3,4,6-Tetrachloroanisole and pentachloroanisole were found at ppm level in fat of earthworms.

Bioaccumulation of organochlorine compounds in earthworms

Abstract Bioaccumulation of chlorophenolic wood preservatives 2,3,4,6-tetrachlorophenol (2346-TeCP) and pentachlorophenol (PeCP) and their metabolites in earthworms were studied in the laboratory, and by taking worm samples from the contaminated soil of a sawmill which was abandoned 28 yr ago. In two laboratory experiments 2346-TeCP (containing PeCP as impurity) was added into the soil, and samples were taken at certain intervals both from the soil and the earthworms ( Lumbricus rubellus in experiment 1 and Aporrectodea caliginosa tuberculata in experiment 2). Considerable amounts of chlorophenols were found in field samples. Soil concentrations ranged from 157 to 338 μg 2346-TeCP g −1 dry soil and from 103 to 140μg PeCP g −1 dry soil. Earthworm concentrations ranged from 270 to 2000 μg 2346-TeCP g −1 fat and from 130 to 1500μg PeCP g −1 fat, respectively. Earthworms also contained chlorinated anisoles (1–20 μg g −1 fat). On the other hand, chlorinated dihydroxybenzenes were not detected in earthworms, while these substances were present in the soil. Concentrations of chlorophenols were higher in A. caliginosa than in Lumbricus spp. In the pot experiments concentrations of chlorophenols in earthworms increased sharply during the experiments, and concentrations as high as 1800 μg g −1 fat were detected after some weeks incubation (in experiment 1, 61 μg chlorophenols g −1 dry soil, and in experiment 2, 154μg chlorophenols g −1 dry soil, was added). The earthworms had no influence on the concentrations of chlorophenols in the soil.

Effects of soil fauna on leaching of nitrogen and phosphorus from experimental systems simulating coniferous forest floor

SummaryLong-term experiments (97–98 weeks) were carried out in macrocosm systems simulating the complexity of coniferous forest soil. The macrocosms were partially sterilized by freezing, thawing and drying, then re-inoculated with microbes alone or microbes + soil fauna. Removable microcosms containing birch litter, spruce litter, or humus were inserted into the substrate humus in the macrocosms. Two experiments used organic matter only, and in the third there was mineral soil below the humus. The macrocosms were incubated in climate chambers that simulated both summer and winter conditions. At 4- to 6-week intervals the substrates were irrigated for analyses of pH, total N, NH4+−N, NO3−−N, and PO43−−P in the leachates. At the end of each growing season a destructive sampling was performed, including analyses of KCl-extractable N and P.Leaching of NH4+and PO43−from both the litter and the total systems was significantly enhanced by the soil fauna. There were also differences in mineralization of N and P between the refaunated systems, apparently due to divergent development of the faunal communities. In general, fauna affected KCl-extractable nutrients from the litter positively, although this effect was less evident than in the leaching water. In the humus and mineral soil the fauna significantly increased the release of N and P, especially in the later stages of the experiments. Soil pH was higher in the presence of fauna, but there was no difference in the pH of the leachates. Not only invertebrate-microbial interactions, but also mutual relationships among fauna were important in the nutrient dynamics.