|Title||Drought suppresses soil predators and promotes root herbivores in mesic, but not in xeric grasslands|
|Publication Type||Journal Article|
|Year of Publication||2019|
|Authors||Franco ALC, Gherardi LA, de Tomasel CM, Andriuzzi WS, Ankrom KE, E. Shaw A, Bach EM, Sala OE, Wall DH|
|Journal||Proceedings of the National Academy of Sciences|
Temporal and spatial variation in precipitation affect the functional composition of biological communities and ecosystems. Belowground, these changes disrupt the fragile balance between root herbivores, which are major constraints of ecosystem primary production, and their predators. We provide evidence that droughts and deluges alter the functional composition of soil nematode communities depending on the long-term mean annual precipitation (MAP) along a gradient from arid to moist grasslands. The abundance of root-feeding nematodes increased under drought following reductions in the number of predators. These responses increased in magnitude along the MAP gradient, demonstrating that climate change can tip the nematode predator-prey balance and result in higher abundance of root herbivores with potentially important implications for mesic grasslands.Precipitation changes among years and locations along gradients of mean annual precipitation (MAP). The way those changes interact and affect populations of soil organisms from arid to moist environments remains unknown. Temporal and spatial changes in precipitation could lead to shifts in functional composition of soil communities that are involved in key aspects of ecosystem functioning such as ecosystem primary production and carbon cycling. We experimentally reduced and increased growing-season precipitation for 2 y in field plots at arid, semiarid, and mesic grasslands to investigate temporal and spatial precipitation controls on the abundance and community functional composition of soil nematodes, a hyper-abundant and functionally diverse metazoan in terrestrial ecosystems. We found that total nematode abundance decreased with greater growing-season precipitation following increases in the abundance of predaceous nematodes that consumed and limited the abundance of nematodes lower in the trophic structure, including root feeders. The magnitude of these nematode responses to temporal changes in precipitation increased along the spatial gradient of long-term MAP, and significant effects only occurred at the mesic site. Contrary to the temporal pattern, nematode abundance increased with greater long-term MAP along the spatial gradient from arid to mesic grasslands. The projected increase in the frequency of extreme dry years in mesic grasslands will therefore weaken predation pressure belowground and increase populations of root-feeding nematodes, potentially leading to higher levels of plant infestation and plant damage that would exacerbate the negative effect of drought on ecosystem primary production and C cycling.