COS 72-8 - Scale-dependent responses of soil invertebrate communities to altered soil moisture regimes across a regional precipitation gradient

Wednesday, August 10, 2011: 4:00 PM
6A, Austin Convention Center
Zachary A. Sylvain and Diana H. Wall, Department of Biology and Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO

Climate models predict alterations to precipitation regimes over the next century, with an increase in extreme events leading to larger precipitation events with increased variability in inter-event duration. These alterations may result in prolonged periods of drought, which will impact soil moisture, an important ecosystem variable that influences plant productivity, nutrient availability and habitat space for soil organisms. Soil organisms such as mites and nematodes play important roles in ecosystem processes including decomposition and nutrient cycling, and alterations to soil moisture may result in changes to community structure of these two groups and subsequently their contributions to ecosystem processes.

Plots were established in four long-term ecological research (LTER) sites: the McMurdo Dry Valleys, Antarctica and three sites (Konza Prairie, KS; Shortgrass Steppe, CO; Jornada Basin, NM) along a regional-scale precipitation gradient across the mid- and south-west US. A transect of three plots at different slope positions was established at each site to delineate a natural soil moisture gradient across the landscape, and existing precipitation manipulations were sampled to obtain data on soil moistures pushed beyond natural variation. Sampling was carried out in fall 2009 and before, during and after the wet season of 2010 in each site. 


ANOVA results revealed differences in nematode trophic group distributions: plant parasites were dominant within Konza Prairie and made up nearly half of all nematodes collected from all sites, while bacterial feeders dominated in the McMurdo Dry Valleys. Regression analyses revealed patterns observed at the regional scale (including all sites) differed from those at the landscape scale (across individual sites); for example, bacterial feeders exhibited a significant negative relationship with soil moisture at the regional scale while at the landscape scale a significant positive relationship was observed at Konza. In contrast, predators showed a positive relationship with soil moisture at the regional scale, but a negative trend at the Shortgrass Steppe. Results on mite data will also be presented; identification is currently ongoing.

These results suggest that soil moisture is an important variable in structuring soil invertebrate populations at multiple scales, although responses appear to be scale- and in some cases ecosystem-dependent. Notably, invertebrates at the wettest site (Konza) appear to respond differently than those at drier sites, a factor that may be influenced by aboveground productivity. Future work will correlate changes in soil invertebrate communities with variation in other ecosystem variables to tease apart these responses.

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