Jari Haimi

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.

Responses of soil decomposer animals to wood-ash fertilisation and burning in a coniferous forest stand

Abstract Responses of soil decomposer animals (enchytraeids and microarthropods) to wood-ash fertilisation (1000 and 5000xa0kgxa0ha−1) and a fire treatment mimicking prescribed burning were studied in a Scots pine stand in central Finland. The experiment was conducted on 30xa0×xa030xa0m2 plots, each treatment being replicated four times. Soil animals were sampled throughout the growing season in the third year after the treatments. As a rule, numbers of soil animals increased during the study period. Numbers of the only enchytraeid worm species found at the study site, Cognettia sphagnetorum, were lower in the plots with higher ash level and plots which have been burned. In the plots having these treatments, enchytraeid populations increased during the study period. Total numbers of microarthropods were decreased in the plots which had received the most drastic treatments: the higher ash level and burning. Only five species of collembolas responded significantly to these treatments. Multivariate analyses showed, however, significant changes in the collembola community structure of all the treatments. Overall, soil fauna seemed to be quite resistant and resilient against unpredictable disturbances, like ash fertilisation and prescribed burning, the thick humus layer being a major buffer against chemical and physical changes.

Sensitivity of soil processes in northern forest soils: are management practices a threat?

Abstract There is evidence that forest management practices influence soil-decomposer communities. It is also established that changes in the trophic structure and composition of these communities can induce changes in soil-nutrient dynamics, thereby affecting plant growth. Whether forest productivity is affected by management-induced changes in, e.g. soil faunal structure, is, however, yet to be shown. The aim of this study was (1) to determine the resolution of the ecological hierarchy (e.g. species, functional groups, trophic levels) at which a change in soil fauna would alter biotically-controlled processes in soils, and (2) to examine the sensitivity of soil fauna of the boreal forest floor to various kinds of forest management practices. A review of laboratory miniecosystem experiments carried out at the University of Jyvaskyla is presented to examine the diversity-ecosystem function relationship. The response of tree growth to manipulation of soil-faunal composition was measured. A field experiment was conducted in central Finland in spruce stands, including several stand management treatments in addition to the untreated controls. The fellings took place in winter 1996, and various groups of soil animals have been sampled since 1995. Laboratory experiments revealed that soil processes and plant growth are largely insensitive to changes taking place at the species level of soil fauna. Some important keystone species may exist, but a change in the functional group architecture seems to be a prerequisite for altered rates in soil processes. Predators high up in the detrital food web had no detectable influence on any of the ecosystem-level processes. In the field, all of the faunal groups studied proved to be highly insensitive to the stand management practices. As compared to the untreated controls, numbers of enchytraeid worms, collembolans and most of the macroarthropods in the managed stands were not significantly different. It is concluded that management practices with minor impacts on the soil organic layer, which buffers soil biota against drastic changes in their environment, have little influence on biotically-controlled soil processes.

Influence of Cognettia sphagnetorum (Enchytraeidae) on birch growth and microbial activity, composition and biomass in soil with or without wood ash

Abstract. In this laboratory study using microcosms with seedlings of silver birch (Betula pendula), we explored whether Cognettia sphagnetorum (Enchytraeidae) can retain its important role of accelerating decomposition processes in soils and stimulating primary production under disturbance. We established systems with or without wood ash amendment (first-order disturbance) in the soil, either in the presence or absence of C. sphagnetorum. To test whether the systems treated with wood ash are more sensitive to an additional disturbance than the ash-free systems, the microcosms were later on disturbed by drought. To determine the influence of two disturbances on the enchytraeids and populations of other fauna, and the possible changes in the system functioning, measurements were made of the growth of birch seedlings, foliar N concentration, composition and biomass of soil microbial communities and leaching of N and dissolved organic carbon from the microcosms. Both wood ash application and drought exerted a clear negative influence on the populations of C. sphagnetorum. However, populations of this species were very resilient and recovered rapidly after drought in the ash-free soils. In the ash-free soils C. sphagnetorum tended to improve birch growth, increased the N content of the birch leaves, and decreased the root to shoot ratio. However, in the ash-treated soils enchytraeids had negative effects on these parameters. C. sphagnetorum impacted on neither N and C leaching nor soil microbes, whereas wood ash decreased microbial biomasses and changed their community structure (as determined by phospholipid fatty acids method and denaturing gel electrophoresis) and substrate utilisation potential (Biolog method). It was concluded that C. sphagnetorum can retain its influential role under varying environmental conditions, but that the stimulating or retarding effects of this species on system functioning can be context dependent.

Effects of stump removal on soil decomposer communities in undisturbed patches of the forest floor.

Abstract Soil preparation after clear-cutting leads to fragmentation of forest floor and, consequently, changes the habitat of decomposers. Stump removal for bioenergy is further increasing the disturbance in the soil. We studied responses of decomposers to stump removal in boreal spruce forests during the first 4 years after clear felling in relation to mounding. Samples for each decomposer organism group were taken from undisturbed forest floor patches that are the main habitat for decomposers after forest regeneration and whose amount and size obviously differ between the treatments. Microbial biomasses and community structure, and the abundance of enchytraeids, were not found to be affected by the stump removal. The abundance of nematodes and the total numbers of collembolans were lower in the stump harvesting plots compared with the mounded plots 3 years after the regeneration. In addition, microbivorous macroarthropods had higher abundances in the mounded plots. Together, decomposer community in the fragments of undisturbed forest floor only slightly differed between the mounded and stump removal areas. However, more data are urgently needed to also find out the longer-term effects of stump removal on the forest soil decomposers and their functioning and the development of decomposer community in exposed mineral soil.

Regulation of decomposer community structure and decomposition processes in herbicide stressed humus soil

Abstract Regulation of soil decomposer community structure and ecosystem processes, such as nutrient cycling, under herbicide stress was studied in a microcosm experiment. For the experiment, coniferous forest soil was defaunated and put into the microcosms. In the microcosms two different food webs including microbes, nematodes, tardigrades and oribatid mites, either with or without predatory mesostigmatid mites, were reconstructed. Half of the microcosms were stressed with a herbicide (active ingredient was terbuthylazine). During the 57 weeks incubation community structure of decomposers and nitrogen mineralisation were studied at five destructive samplings and two water irrigations. Soil respiration was measured weekly starting at week 26. Mesostigmatid mites regulated densities of some prey species and hence they had an effect on the community structure of microbivores. A trophic cascade from predators to microbes took place both in unstressed and stressed soils: microbial activity decreased in the presence of predators. Predation effect was observed more clearly in the unstressed soil although predators maintained their populations longer in the herbicide stressed soil. Predators had no significant effects on N mineralisation while herbicide increased it. Oribatids were reduced by the herbicide at the later phase of the experiment. It can be concluded that decomposer food webs and decomposition in the soil can partly be top-down controlled. Due to a high degree of omnivory it was impossible to determine precisely the trophic structure of the food web. Herbicide contamination altered the community regulation and ecosystem processes via direct toxicity and by affecting trophic interactions. Although the application of food web analysis in risk assessment procedures has been proved to be problematic, there is a clear need for system level studies because of the chemical-induced indirect effects on the food webs.

Role of the fauna in soil processes: techniques using simulated forest floor

Abstract Laboratory experiments were conducted to test the influence of soil animals on processes such as decomposition, nutrient cycling, and plant growth in northern coniferous forests. The techniques included simulation of a complex pattern of forest floor, controlled air flow through the systems, and automatic measurement of carbon flows. The soil fauna generally enhanced evolution of CO2 and mineralization of N and P from soil and litter, and increased considerably the biomass production and N content of birch seedlings. Significant results were also obtained on interactions between different faunal components.

The asexual enchytraeid worm Cognettia sphagnetorum (Oligochaeta) has increased Cu resistance in polluted soil

We studied Cu resistance in the asexual (reproduction through fragmentation) enchytraeid worms (Cognettia sphagnetorum, Oligochaeta) originating from two sites: one uncontaminated, and another contaminated by heavy metals. Adult worms were smaller and population density was lower at the polluted site. However, adults from the contaminated site had better survival in Cu-contaminated soil, but lower survival as juveniles (fragments). As we do not know the genetic basis of Cu resistance of the worms, it may have been reached by acclimatization via induced Cu regulation. Because fragmentation is the only mode of reproduction, all phenotypic properties (including resistance) of a parental generation could be transferred to filial generations.

Does stump removal affect early growth and mycorrhizal infection of spruce (Picea abies) seedlings in clear-cuts?

Abstract Stump removal procedure increases the extent of exposed mineral soil in the clear felled areas. In this study, our aim was to find out whether the early growth and mycorrhization of Norway spruce (Picea abies (L.) Karst.) seedlings differ between stump removal and mounding sites. Stumps were harvested from five one-hectare study sites and other five sites were mounded after clear felling. Twenty seedlings were planted on mounds at each study site. Although the height of spruce seedlings did not differ between the treatments after three growing periods, their mean growth was ca. 10% higher at the stump removal sites. The community of ectomycorrhizal (ECM) in the seedling roots did not differ between the treatments. The high mycorrhization rate in the nursery still remained after two and three growing seasons in the field and diversity of ECM community slightly increased during the first years. Our results indicate some positive although rather small and transient effects of stump removal on the performance of planted spruce seedlings. Longer-term studies are needed to fully understand the effects of stump removal on the later seedling development and their symbiotic interactions with mycorrhizal fungi.

Solar ultraviolet radiation alters alder and birch litter chemistry that in turn affects decomposers and soil respiration

Solar ultraviolet (UV)-A and UV-B radiation were excluded from branches of grey alder (Alnus incana) and white birch (Betula pubescens) trees in a field experiment. Leaf litter collected from these trees was used in microcosm experiments under laboratory conditions. The aim was to evaluate the effects of the different UV treatments on litter chemical quality (phenolic compounds, C, N and lignin) and the subsequent effects of these changes on soil fauna and decomposition processes. We measured the decomposition rate of litter, growth of woodlice (Porcellio scaber), soil microbial respiration and abundance of nematodes and enchytraeid worms. In addition, the chemical quality of woodlice feces was analyzed. The exclusion of both UV-A and UV-B had several effects on litter chemistry. Exclusion of UV-B radiation decreased the C content in litter in both tree species. In alder litter, UV exclusion affected concentration of phenolic groups variably, whereas in birch litter there were no significant differences in phenolic compounds. Moreover, further effects on microbial respiration and chemical quality of woodlice feces were apparent. In both tree species, microbial CO2 evolution was lower in soil with litter produced under exclusion of both UV-A and UV-B radiation when compared to soil with control litter. The N content was higher in the feces of woodlice eating alder litter produced under exclusion of both UV-A and UV-B compared to the control. In addition, there were small changes in the concentration of individual phenolic compounds analyzed from woodlice feces. Our results demonstrate that both UV-A and UV-B alter litter chemistry which in turn affects decomposition processes.