Hidden Decomposers: the Role of Bacteria and Fungi in Recently Intermittent Alpine Streams Heterotrophic Pathways

Abstract

The frequency of flow intermittency and drying events in Alpine rivers is expected to increase due to climate change. These events can have significant consequences for stream ecological communities, though the effects of reduced flow conditions on microbial communities of decomposing allochthonous leaf material require additional research. In this study, we investigated the bacterial and fungal communities associated with the decomposition of two common species of leaf litter, chestnut (Castanea sativa), and oak (Quercus robur). A sampling of experimentally placed leaf bags occurred over six collection dates (up to 126 days after placement) at seven stream sites in the Western Italian Alps with historically different flow conditions. Leaf-associated bacterial and fungal communities were identified using amplicon-based, high-throughput sequencing. Chestnut and oak leaf material harbored distinct bacterial and fungal communities, with a number of taxonomic groups differing in abundance, though bacterial community structure converged later in decomposition. Historical flow conditions (intermittent vs perennial rivers) and observed conditions (normal flow, low flow, ongoing drying event) had weaker effects on bacterial and fungal communities compared to leaf type and collection date (i.e., length of decomposition). Our findings highlight the importance of leaf characteristics (e.g., C:N ratios, recalcitrance) to the in-stream conditioning of leaf litter and a need for additional investigations of drying events in Alpine streams. This study provides new information on the microbial role in leaf litter decomposition with expected flow changes associated with a global change scenario.

Reciprocal stream–riparian fluxes: effects of distinct exposure patterns on litter decomposition

“…The present results were likely modulated by the leaf species and environmental conditions; litter species-specific responses to distinct exposure patterns have been suggested in previous works (Dieter et al 2013;Abelho and Descals 2019;Gruppuso et al 2023). Even though the recalcitrance of ligninrich and N-poor substrata can be reduced by terrestrial exposure (through photodegradation decomposing lignin and increasing nitrogen content) (Pu et al 2014), in our work the dense canopy and the abundance of litter on the ground seems to have clearly limited light exposure.…”

Biodiversity of Fungi in Freshwater Ecosystems of Italy

“…Later, Angelini and coworkers [50], Duarte and coworkers [51], and Davolos and coworkers [52] published the first surveys on freshwater Ascomycota in lakes and rivers from central Italy (Trasimeno Lake, Umbria; Bracciano Lake and Sacco River, Lazio). Finally, other studies about freshwater Ascomycota were published by Bizio and Borsato [53], and Gruppuso and coworkers [54], carried out in Cansiglio forest (Veneto), and Alpine streams of Piemonte, respectively. Z. marina Roots of P. australis Trasimeno Lake, Umbria [50] Incertae sedis…”