Nematode-trapping fungi of a natural shrubland: Tests for food chain involvement

Abstract

We describe the spatial and temporal pat- terns in the abundance of nematode-trapping fungi and in suppression of nematodes in a coastal shrub- land. A previous study at this location (Bodega Ma- rine Reserve, Sonoma County, California) had doc- umented a soil food chain in which an insect-parasitic nematode consumes and kills the soil-dwelling larva of the ghost moth, which otherwise consumes and kills the bush lupine; the patchy distribution of the nematode and lupine suggest the involvement of ne- matophagous organisms, including nematode-trap- ping fungi. To test our model (trapping fungi kill insect-parasitic nematodes, and therefore ghost moths persist and kill lupines at some sites), we hy- pothesized that sites with substantial lupine mortality would contain larger numbers of nematode-trapping fungi and would be more suppressive to nematodes than would sites with little lupine mortality. Soil was collected from eight sites (four with substantial lu- pine mortality and four with little lupine mortality) at 2-mo intervals for 1 yr and subjected to dilution plating and most probable number procedures. Nematode-trapping fungi detected were Arthrobotrys brochopaga, A. musiformis, A. oligospora, A. superba, Geniculifera paucispora, Hirsutella rhossiliensis, Mon- acrosporium cionopagum, M. doedycoides, M. euder- matum, M. parvicollis, Nematoctonus concurrens, and Stylopage sp. A. oligospora was the most abundant. Some soil samples contained large numbers of nem- atode-trapping fungi (as many as 695 propagules/g of soil), but sites with substantial lupine mortality did not contain larger numbers than did sites with little mortality. In a laboratory bioassay, suppression of the