A MICROCOSM STUDY OF THE EFFECTS OF CHEMICAL STRESS, EARTHWORMS AND MICROORGANISMS AND THEIR INTERACTIONS UPON LITTER DECOMPOSITION

The effects of four factors and their interactions on litter decomposi tion, earthworm (Lumbricus terrestris L.) biomass and on microbial bio mass in litter and soil were investigated in a laboratory experiment u sing microcosms. The factors chosen were soil type, mesh width of litt erbags, watering rate and application rate of the fungicide carbendazi m. Separate factorial experiments were conducted with ''grassland'' an d ''forest'' microcosms. The ''grassland'' microcosms contained soil a mended with litter from the same grassland whereas the ''forest'' micr ocosms contained soil and litter from a beech forest. Five earthworms were placed in each microcosm and kept at a temperature of 10 degrees C for four weeks. The results indicated that the most significant effe ct was that of a toxic effect of the carbendazim upon the earthworms. This in turn suppressed the selective feeding of the worms on the micr obially well-colonized parts of the litter and thereby indirectly affe cted the decomposition process. Whilst there were no direct effects of the carbendazim upon microbial biomass and respiratory activity in th e soil and the litter, there was a clear indirect effect of the chemic al upon the microbial quality of the aboveground litter due to its eff ects on the selective feeding activity of the earthworms. The results of these factorial design experiments demonstrated that complex microc osm test systems are effective tools for the analysis of indirect effe cts of chemicals on integrative ecosystem level parameters such as the decomposition process.