One for the road: Aspect-linked temperature variation affects earthworm community structure but not litter decomposition

Anthropogenic climate change is widely predicted to influence essential ecosystem services such as decomposition and nutrient cycling, but consistent patterns of response to observed or predicted shifts in climate have proven difficult to evidence. We investigated how aspect (i.e., Pole- (PF) and Equator-facing (EF) roadside grassy verges in SW England), a natural model for variation in soil temperature, influenced soil physicochemical conditions, earthworm communities, and oak leaf litter decomposition. Average above-ground daily annual temperatures for EF-slopes were 1.96 °C higher than PF-slopes, with even more marked variation in average mean daily maximum and extreme temperatures (i.e., an average of three-fold more days where temperature exceeded 30 °C). Despite these differences, of the soil physicochemical factors quantified, only soil moisture (0–15 cm deep) varied consistently with aspect, being higher on the cooler PF slopes. Similarly, we detected no significant variation in litter decomposition. Despite low abundances there were, however, differences in earthworm assemblages between PF- and EF- slopes, with 7 of 14 species restricted to cooler, moister PF verges. Consequently, we conclude that despite consistent aspect-linked differences in the local microclimate, soil-based patterns and processes in semi-natural, temperate grassland ecosystems are relatively well buffered from the magnitude of temperature variation within the range predicted by the IPCC SSP1-2.6 emissions scenario. Nonetheless, the restricted distribution of half the earthworm species, and two functional groups to PF-slopes, supports studies suggesting that temperate increases associated with higher emissions scenarios will negatively influence some species, and the vital soil bioturbation processes that they provide.