DECOMPOSITION OF BEECH LEAF-LITTER BY MICROFLORA AND MESOFAUNA .2. FOOD PREFERENCES AND ACTION OF ORIBATID MITES ON DIFFERENT SUBSTRATES

The food preferences and the decomposing activity of three oribatid mi tes, Steganacarus magnus, Achipteria coleoptrata and Damaeus verticill ipes, were studied using twelve different substrates, ranging from not decomposed beech leaves, to beech leaves that were partially decompos ed by two white-rot fungi (Basidiomycetes), Sporotrichum pulverulentum (strain SPU) and one species from Fontainebleau Forest (strain FTS). In addition, one group of leaves was bleached chemically. The main dif ferential food preferences were as follows: A) S. magnus - 1) beech li tter bleached during 16 hours by NaClO; 2) beech litter decomposed dur ing one month by FTS; 3) beech litter decomposed during one week by FT S; B) A; coleoptrata - 1) cellulose + polyphenols; 2) mycelium SPU; 3) beech litter not decomposed; 4) beech litter decomposed during one we ek by SPU; C) D. verticillipes - 1) mycelium FTS; 2) beech litter deco mposed during one month by SPU. It should be noted that the oribatid p references for the fungi (mycelium) were, in two out of three species, different from their preferential action on the leaves decomposed by the same fungi. Furthermore, and in conclusion, the association betwee n oribatid mites and white-rot fungi increased the consumption rate of the beech leaves (litter) and, in that way, their rate of decompositi on.