Increased frequency of drought reduces species richness of enchytraeid communities in both wet and dry heathland soils

Studies of biological responses in the terrestrial environment to rapid changes in climate have mostly
been concerned with above-ground biota, whereas less is known of belowground organisms. The present
study focuses on enchytraeids (Oligochaeta) of heathland ecosystems and how the enchytraeid
community has responded to simulated climate change in a long-term field experiment. Either increased
temperature or repeated drought was applied for 13 years to field plots located in Wales, The
Netherlands and Denmark representing a gradient in precipitation and annual temperature fluctuations
thereby providing an opportunity to study biological responses on a local (within sites) and regional
scale. Warming treatments increasing night-time temperature (0.5e1 C higher than ambient at 5 cm
soil depth) had no detectable effects on the enchytraeid communities. Increased intensity and frequency
of drought had rather weak persistent effects on total enchytraeid abundance suggesting that ecosystem
functions of enchytraeids may only be transiently impacted by repeated spring or summer drought.
However, drought treatment had persistent negative effects on species richness and community structure
across sites. Drought treated plots harboured only 35e65% of the species present in control plots,
and the reduction of species richness was most pronounced at the driest sites. It is discussed that soil
invertebrates, due to their weak migratory potential, may be more liable to extinction under changing
climatic conditions than above-ground species, and therefore consequences of climate change to soil
organisms need particular attention in future research.