Effects of a one-year rainfall manipulation on soil nematode abundances and community composition

Soil nematodes play a crucial role in the terrestrial nitrogen cycle by accelerating the release of ammonium from microorganisms (bacteria and fungi). As aquatic organisms, nematodes are likely to be affected by predicted changes in precipitation patterns and soil moisture during the 21st century. The objective of this study was to measure the response of soil nematodes to a one-year rainfall manipulation in the sandy, forest soils of the New Jersey Pinelands (USA). We excluded all rain from four replicate field plots and applied double the amount of natural rainfall to four additional plots. We then assessed the impact of these precipitation treatments on nematode abundance and community composition. We found that total nematode abundance increased with more precipitation, and were highly sensitive to annual precipitation amount. This is in contrast to microbial biomass which was previously found to be insensitive to precipitation change. We suggest that any increased microbial growth in high rainfall plots was consumed by microbivorous nematodes. We further suggest that nematodes in the freely draining, sandy soils we studied may be unsuccessful at surviving drought because few water-filled pore spaces remain, as compared to more aggregated soils. All nematode families were sensitive to drought, but the effect was greatest on the Plectidae, while no significant effects were found for the Cephalobidae and Qudsianematidae. While not directly measured, these results provide insight into the relative anhydrobiotic abilities of these families. We found that bacterial-feeding nematodes were most sensitive to drought, suggesting that grazer-induced alterations to the nitrogen cycle are possible if precipitation patterns change in the future.