EFFECT OF AN ANNUAL AND A PERENNIAL CROP ON TROPHIC GROUP DYNAMICS OF NEMATODES

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Abstract
Adult and juvenile nematode distribution and trophic group dynamics were studied in oat (Avena sativa L.) and alfalfa (Medicago sativa L.) plots of a 5-yr rotation at Breton, Alberta. Nematodes were separated into two groups: (i) adults including the late juveniles and (ii) juveniles. The adults and the late juveniles were further separated into four trophic groups: (i) plant parasites, (ii) microbivores, (iii) miscellaneous feeders and (iv) predators. Adults accounted for 83% of the total population in the oat plot and 79% in the alfalfa plot. There were no significant differences in percent distribution of adults between plots over the season or at a given date. The average density of adults over the season in the oat plot (3.3 × 106 individuals m−2) was greater than that in alfalfa plot (2.1 × 106 individuals m−2, P < 0.001). Adult density in the oat plot increased steadily from 3.2 × 106 to 4.2 × 106 individuals m−2 between July and September. There was a sharp decline after harvest. In contrast, the adult population in the alfalfa plot remained steady over the growing season. Juvenile density showed similar trends as the adults. Distribution of microbivores, plant parasites, miscellaneous feeders, and predators, was 63, 22, 13, and 2% in oat and 51, 34, 13, and 2% in alfalfa plot, respectively. Crop effect on microbivores and plant parasites was significant at P < 0.05. Our study showed that microbivores are the dominant group in cultivated soils and plant parasites build up in the presence of living roots. Key words: Microbivores, miscellaneous feeders, nematodes, plants parasites, predators, trophic groups

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