[Interactions between fungal-feeding nematodes and fungi and their effects on soil nitrogen mineralization]

A species of fungal-feeding nematodes (Aphelenchus avenae) and two species of fungi (Micheli corticolus and Moniliaceae sp.) were isolated from an alluvial soil planted with paddy-rice and wheat in subtropical region. In order to approach their interactions and effects on soil nitrogen mineralization, a gnotobiotic microcosm experiment was carried out with four treatments, i.e., 1) soil + fungi-I (M. corticolus), 2) soil + fungi I + Aphelenchus avenae, 3) soil + fungi II (Moniliaceae sp.), and 4) soil + fungi II + Aphelenchus avenae at 22 degrees C for 25 days. The results showed that the individuals of nematode and fungi were increased simultaneously, suggesting that the inoculation of A. avenae stimulated the growth of fungi. The fungal-feeding nematode increased during the initial 20 days of incubation and then decreased slowly, and the individuals of the nematode that fed on Moniliaceae sp. (II) were higher than those fed on M. corticolus (I) (P<0.01). In the first 12 days of incubation, the population of Moniliaceae sp. (II) increased 2.5-3.5 times, while that of M. corticolus (I) increased slower but caught up after the 12th day, and the density reached 5.0-5.7 times higher than the corresponding treatments with only fungi inoculation. The interactions encouraged the soil nitrogen mineralization of all four treatments, as compared with the control. Comparing the treatments with and without fungal-feeding nematode inoculation, the treatments with fungal-feeding nematode had a higher content of soil NH4+-N than those with only fungi inoculations, which indicated that nematode had a greater effect on soil nitrogen mineralization than fungi. As for the two species of fungi, M. corticolus (I) had a greater effect on soil nitrogen mineralization than Moniliaceae sp. (II). It was observed, however, that the nitrification rate declined as compared with the control.