No abstract

The study of leaf litter as a resource for shredders has emerged as a key topic in trophic links in ecology. However, thus far, most studies have emphasized the leaf quality as one of the main determinants of shredder behaviour and growth without simultaneously considering the leaf quantity availability. Nevertheless, the combined effects of leaf quantity and quality on shredder behaviour and growth is particularly crucial to further understand how ecosystem functioning may respond to the increasing flow intermittency due to climate change. In this study, we explore how changes in the leaf litter quality and quantity influence the feeding preferences and growth of an invertebrate shredder (Potamophylax latipennis). To do so, we used black poplar leaves conditioned in two streams with different flow regimens as a food resource. Afterwards, using a microcosm approach, we offered leaf discs that varied in terms of leaf quantity and quality to P. latipennis. Our results showed that flow intermittency had a negative effect on the quality of the food resource, and a lower quality had a negative effect on the consumption and growth rates of P. latipennis. Furthermore, we found that P. latipennis fed selectively on higher quality leaves even though the availability (quantity) of this resource was lower. In the context of climate change, with higher aridity/drier conditions/scenarios, our findings suggest that a decrease in the availability (quantity) of high-quality resources could potentially threaten links in global fluvial food webs and thus threaten ecosystem functioning.

Summary Microbes inhabiting intermittent streambeds are responsible for controlling and developing many biogeochemical processes essential for the ecosystem functions. Although streambed microbiota is adapted to intermittency the intensification of water scarcity and prolonged dry periods may jeopardise their capacity to cope with hydrological changes. This study aims to evaluate whether, and to what extent, the duration of dry periods affects streambed microbial density, diversity, composition (16S rRNA gene diversity) and functions (extracellular enzyme activities and respiration). Our results highlight the fact that hydrology modulates the community composition and, to some extent, the functions carried out under different environmental conditions. The relative abundance of certain taxa inhabiting the driest intermittent communities differs significantly from those found at sites with continuous flow. Microbial functional metrics revealed a progressive increase in recalcitrant carbon degradation activity at sites with an extended dry phase. In contrast, bacterial density and diversity were mainly influenced by the catchment land use, agriculture enhanced density but reduced diversity, and the presence of riparian vegetation supported greater streambed bacterial diversity. From this perspective, a combination of prolonged dryness with reduced riparian vegetation and increased agricultural land cover could compromise the ecosystem functioning by threaten microbially mediated processes linked to the carbon cycle.