Biol Fertil Soils (1996) 23:182-188 9 Springer-Verlag 1996 J. Salminen 9J. Haimi Effects of pentachlorophenol in forest soil: a microcosm experiment for testing ecosystem responses to anthropogenic stress Received: 7 June 1995 Abstract Changes in the structure and function of a soil decomposer community and growth of birch (Betula pen- dula) due to chemical contamination were studied in la- boratory microcosms. Sodium pentachlorophenate (PCP) was added to the humus layer of a simulated forest soil at three nominal concentrations (0, 50 and 500 mg kg -1 dry mass). After two growing periods (48 weeks), there were more small soft-bodied mites, but less collembolans and microbial biomass, in the higher PCP concentration treat- ment than in the other treatments. Number of enchytraeids were significantly reduced and fungal-feeding nematodes became extinct in the soil with the higher PCP concentra- tion. Soil respiration did not change due to PCP contami- nation. Diversity of soil fauna tended to decrease with increasing PCP concentration. Number of faunal taxa were not influenced by PCR Mainly due to reduction of enchy- traeids, total animal biomass was significantly lower in the higher PCP concentration treatment than in the other treat= ments. At week 8, leaching of nutrients was greatest in the higher PCP concentration treatment. At the end of the ex- periment no significant changes in soil pH and NH~-N content of the soil were found. Birch growth and N con- centration of the leaves were reduced with the higher PCP concentration. We assume that direct toxicity of PCP at the beginning of the experiment and changes in the de- composer community structure (mainly reduction of en- chytraeids and changes in microfiora) due to PCP were responsible for the lowered primary production in the sys- tems. Key words Anthropogenic stress - Soil communities 9 Decomposition 9 Plant growth 9 Microcosms J. Salminen - J. Haimi ( ~ ) Department of Biological and Environmental Science, University of Jyv~iskylg, PO Box 35, FIN-40351, Jyv~iskylfi, Finland J. Salminen Finnish Environment Agency, PO Box 140, FIN-00251 Helsinki, Finland Introduction Effects of anthropogenic stress at community and ecosys- tem levels have been widely discussed (Odum 1985; Rap- port et al. 1985; Schindler 1987; Gray 1989). Many stud- ies have been done in natural ecosystems and in micro- cosms to study the responses of ecosystems to pollution or other human activities at higher organisation levels (e.g. Barrett 1968; Hurd and Wolf 1974; van Voris et al. 1980; Rapport 1989; Schindler 1990; Havens 1994). In aquatic ecosystems, structural responses, such as decrease in diver- sity, increase in opportunistic species or decrease in size of organisms, are suitable early warning criteria for anthropo- genic stress (e.g. Schindler 1987; Gray 1989). Changes in food web configurations can also be a sign of the presence of stress (Havens 1994). On the other hand, studies with soil microcosms have shown that functional responses of the system can be even better indicators of stress. Perfor- mance in decomposition rate and nutrient cycling have ap- peared to be more sensitive to stress than structural param- eters of the communities (e.g. O'Neill et al. 1977; Jackson et al. 1977). Thus, both structural and functional param- eters can provide valuable information when the effects of stress are evaluated (Barrett et al. 1976). In the present work we studied the consequences of anthropogenic stress in boreal forest soil. We used terres- trial microcosms with birch seedlings and soil decomposer organisms as a model ecosystem. We stressed the system with sodium pentachlorophenate (PCP), a highly toxic non-selective pesticide which is widely used around the world (Hobbs et al. 1993). Its degradation rate is particu- larly low in northern humus rich soils (Knuutinen et al. 1990) and, thus, chemical stress of this kind can be re- garded to be chronic in the system. We used two concen- trations of PCP and an uncontaminated control. In humus soil, the used concentrations have been found to have sub- lethal effects on nematodes and collembolans. The higher concentration is lethally toxic to enchytraeids (Salminen et al. 1995). Our main questions were: what happens to: (1) the community structure (e.g. diversity, biomass, species corn-