A comparison of microbial-feeding nematodes and protozoa in the rhizosphere of different plants

Summary

The biomass of microbial-feeding nematodes and protozoa was measured in the rhizospheres of peas, barley, grass and turnips grown for 10 weeks in pots containing a clay-loam soil; in the rhizospheres of peas and barley grown for 3 weeks in a sandy soil; and in the rhizosphere of barley grown for 11 weeks in an unfertilised and a fertilised clay-loam soil. The nematode biomass was consistently larger in the rhizosphere of all plants in both soils than in the bulk soil, but the protozoa biomass showed a rhizosphere effect only under pea and fertilised barley. The biomass of nematodes in the rhizosphere (1.2–22.3 μg dry weight g^-1 dry soil) was greater than the biomass of protozoa (0.1–3.2 μg g^-1), and greater under pea>barley>grass>turnip. It is suggested that nematodes are more able to exploit low bacterial densities than protozoa and that they initially migrate into the rhizosphere from the bulk soil. In samples of potato rhizosphere from field-grown plants, the nematode biomass was also greater than the active and total protozoan biomass. It is argued that in the rhizosphere the biomass of microbially feeding nematodes exceeds that of protozoa and that nematodes are more important in terms of nutrient cycling.