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 aboveground biota, whereas less is known of belowground organisms. The present study focuses on enchytraeids (Oligochaeta) of heathland ecosystems and how the enchytraeid community have responded to simulated climate change in a long-term field experiment. Increased temperature and repeated drought was applied for 13 years to field plots located in Wales, The Netherlands and Denmark providing an opportunity to study biological responses on a local (within sites) and regional scale representing a gradient in precipitation and annual temperature fluctuations. Warming treatments increasing night time temperature (0.5-1°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 are only transiently impacted by spring or summer drought. However, drought treatment had persistent effects on species richness and community structure across sites. Drought treated plots harboured only 35-65% 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.