Warming, and the presence of a dominant shredder, drive variation in decomposer communities in a mountain stream

Abstract

We assessed the effects of rising temperature and presence of a dominant detritivore (Allogamus laureatus; Trichoptera, Limnephilidae) on the decomposition of submerged oak litter (Quercus robur L.) and associated detritivore and fungal communities in a mountain stream in central Portugal. It was divided longitudinally, with one half maintained at ambient temperature (mean = 12.4 C) while the other was warmed *3 C above ambient temperature. Oak leaves in litter bags were incubated in both stream halves, with half of the bags containing one A. laureatus larva. Replicate bags were collected over 6 weeks to determine litter mass remaining and the detritivore and fungal communities. A. laureatus stimulated decomposition of oak litter and colonization by other shredders at ambient temperature. It also increased fungal biomass at increased temperature, and changed the community of fungi. Higher temperature inhibited A. laureatus activity, resulting in a substantial change in the strength of interactions within both fungal and detritivore assemblages, with important consequences for leaf litter decomposition.