Soil animal community structuring along an LTER cross-site moisture gradient

Changes to precipitation regimes are forecasted in many climate models. The central US is predicted to have potentially fewer, but more extreme events that will lead to longer and more frequent periods of drought. Effects on soil systems can include altering moisture availability and soil physical/chemical processes that in turn affect suitability of habitat for animals such as mites and nematodes. These organisms play important roles in decomposition and nutrient cycling dynamics and shifts to their community structuring can influence energy flow through soil food webs.

We established an LTER cross-site precipitation gradient consisting of two grassland (wet – Konza Prairie – KNZ; semi-arid – Shortgrass Steppe – SGS) and two desert (hot – Jornada Basin – JRN; polar – McMurdo Dry Valleys – MCM) sites. Two moisture gradients were used at each site: 1) a landscape-scale topographic transect of three plots along a hill slope, and 2) existing experiments manipulating precipitation amounts. Samples were collected in Fall 2009 and three times each in 2010 and 2011, with mites and nematodes extracted, counted and sorted to trophic groups.

Moisture availability affected nematode community structure at all scales and sites except for JRN, where soil physical characteristics were more important. Decreases in nematode trophic group abundances at the site level were inverse to those at the level of the overall gradient, where all trophic groups (except for bacterivorous nematodes) showed increases with moisture; in contrast, mites showed an influence of moisture only at the overall gradient level (an increase). Observed changes in the relative abundance of bacterivores, fungivores and root-feeding nematodes at each site suggest that changing moisture regimes will alter energy flow patterns through soil food webs and will thus change ecosystem functioning; root feeding nematodes increased at all sites while shifts in bacterial and fungal feeding groups were site-specific. Including belowground responses when designing precipitation alteration studies may thus improve our understanding of ecosystem dynamics affected by this aspect of global change.