SOIL MESOFAUNA DYNAMICS, WHEAT RESIDUE DECOMPOSITION AND NITROGEN MINERALIZATION IN BURIED LITTERBAGS

The effect of soil microarthropods and enchytraeids on the decompositi on of wheat straw in buried litterbags was studied by selective admiss ion and exclusion. Litterbags with 20 mu m mesh size admitted nematode s, but excluded microarthropods, although temporarily. After 27 weeks of incubation part of these litterbags were colonized, probably throug h egg-deposition of mainly fungivorous Collembola and mites. When litt erbags with a complete microarthropod community (1.5 mm mesh size) wer e compared to Litterbags with strongly reduced microarthropod numbers (20 mu m mesh size), no differences between decomposition rates were f ound. However, in colonized 20-mu m mesh bags, we found reduced decomp osition rates compared to the coarse mesh litterbags, probably due to overgrazing of the fungal population by large numbers of fungivorous m icroarthropods. These large numbers might be caused by the absence of predators. Extraction of microarthropods as well as enchytraeids and n ematodes from the coarse mesh litterbags showed a distinct succession during decomposition. The decomposition process was dominated in the f irst phase by bacterivorous nematodes, nematophagous and bacterivorous mites, and in the later phase by fungivorous nematodes, fungivorous a nd omnivorous mites and Collembola, and predatory mites. This successi on is indicative of a sequence from bacterial to fungal dominated deco mposition of the buried organic matter. The results indicate that the decomposition rate is predator controlled.