Effects of soil moisture on soil invertebrate assemblages

Background/Question/Methods Soil moisture affects several aspects of the soil system by supporting plant life, regulating nutrient availability and providing habitat space for microbes and other organisms. Soil invertebrates such as mites (order Acari) and nematodes (phylum Nematoda) play integral roles in decomposition and nutrient cycling dynamics and their communities may be structured in part by soil moisture. Climate change may alter soil moisture, and this may result in changes to mite and nematode assemblages as well as their associated contributions to ecosystem functioning.

We established sites in four long-term ecological research (LTER) sites (Konza Prairie, Kansas; Shortgrass Steppe, Colorado; Jornada Basin, New Mexico; McMurdo Dry Valleys, Antarctica) along a climatic gradient to assess changes in soil invertebrate assemblages due to shifts in soil moisture. A transect of three 5x5m plots was delineated along a soil moisture gradient (wet, intermediate and dry) and pre-existing experimental manipulations of precipitation (addition, removal, no manipulation) were used within each of these sites. Eight soil cores were collected from each sampling plot in autumn of 2009 (January 2010 for McMurdo Dry Valleys) and then bulked to obtain one uniform sample representing plot-level variation. Bulked samples were subsampled for all extractions of mites and nematodes and analyses.

Results/Conclusions ANOVA results revealed differences in nematode trophic group distributions within sites: bacterial feeders were the dominant group in the McMurdo Dry Valleys while plant parasites were dominant in Konza Prairie. Total nematodes were greater in Konza Prairie and the Shortgrass Steppe LTERs than in the Jornada Basin or McMurdo Dry Valleys LTERs and bacterial feeders were more prevalent in the Shortgrass Steppe than the Jornada Basin or Konza Prairie. Data within sites also suggest nematode populations increase with soil moisture (3132 to 5165 nematodes kg^-1 dry soil). Preliminary data for mites will also be presented; identification and sorting is currently in progress.

These results suggest that soil moisture is an important governing variable for soil invertebrate populations at multiple scales. At regional scales where soil moisture variation between areas is controlled by climate, changes in trophic group distributions are observed between the sites used in this study. At landscape and local scales where soil moisture is controlled by topography or experimental manipulation we observe an overall increase in the populations of nematodes. Patterns will be examined over a temporal scale and provide a better picture on the role soil moisture and climate change may play in structuring soil communities.