RECOVERY OF NEMATODES FROM SCOTS PINE SOIL AND LITTER BULK SAMPLES - EFFECTS OF MIXING AND ADDITION OF WATER

The formation of bulk samples is a common procedure in nematological r esearch. In this way average abundances are estimated from heterogenic distribution patterns in the field, with a minimum investment in samp ling and extraction procedures. Detrimental effects of the formation o f bulk samples and especially the homogenization procedure on the reco very of nematodes may be expected. To gain more insight in these effec ts, two types of experiments were carried out with a Scots pine forest soil. In the first type, the recovery from separate soil and litter s amples was compared to mixed bulk samples of the same material. Additi onally effects on genera composition were examined. On average, recove ry of nematodes from mixed soil bulk samples was significantly (40%) l ower than the number from seperate samples. No difference in recovery was found between mixed and separate litter samples, provided that equ al sample masses were used to exclude influence of extraction efficien cy. Genera composition of separate and mixed soil bulk samples did not differ significantly. This may however, also be the result of the abs ence of (larger) disturbance sensitive species in this type of soil ec osystem. In a second (factorial) experiment water was added to a part of the bulk samples, prior to transport. Furthermore recovery was comp ared after homogenization of wet and dry bulk samples. Mixing again ca used a decrease in average nematode recovery from both wet and dry bul k samples (significant for dry samples only). Water had no significant effect on survival during transport and homogenization, despite the f act that there seems to be a certain protection against grinding. Neve rtheless, the two most contrasting treatments, wet-unmixed versus dry- mixed differed (significantly) by a factor 2 in nematode recovery. Eff ects of physical damage to nematodes as a consequence of sampling and extraction procedures should get more attention in ecological and plan t-protection research. There is still uncertainty about the number of disturbance sensitive species and the role of soil structure (type) in the survival of nematodes during sample treatment.