Reduced feeding activity of soil detritivores under warmer and drier conditions

Anthropogenic warming is projected to trigger positive feedbacks to climate by enhancing carbon losses from the soil. While such losses are, in part, due to increased decomposition of organic matter by invertebrate detritivores, it is unknown how detritivore feeding activity will change with warming, especially under drought conditions. Here, using four-year manipulation experiments in two North American boreal forests, we investigate how temperature (ambient, ambient + 1.7 °C and ambient + 3.4 °C) and rainfall (ambient and –40% of the summer precipitation) perturbations influence detritivore feeding activity. In contrast to general expectations, warming had negligible net effects on detritivore feeding activity at ambient precipitation. However, when combined with precipitation reductions, warming decreased feeding activity by ~14%. Across all plots and dates, detritivore feeding activity was positively associated with bulk soil microbial respiration. These results suggest slower rates of decomposition of soil organic matter and thus reduced positive feedbacks to climate under anthropogenic climate change.