Microbial leaf degraders in boreal streams: bringing together stochastic and deterministic regulators of community composition

Abstract

1. Leaves that fall into the water represent a new habitat for microorganisms to colonise in streams, providing an opportunity to study colonisation and the subsequent regulation of community structure. We explored community composition of bacteria and fungi on decomposing alder leaves in nine streams in central Sweden, and describe their relationship with environmental variables. Succession of the microbial community was studied in one of the streams for 118 days. Microbial community composition was examined by denaturing gradient gel electrophoresis on replicate samples of leaves from each stream. 2. During succession in one stream, maximum taxon richness was reached after 34 days for bacteria and 20 days for fungi respectively. Replicate samples within this stream differed between each other earlier in colonisation, while subsequently such variation among replicate communities was low and remained stable for several weeks. Replicate samples taken from all the nine streams after 34 days of succession showed striking similarities in microbial communities within-streams, although communities differed more strongly between streams. 3. Canonical analysis of microbial communities and environmental variables revealed that water chemistry had a significant influence on community composition. This influence was superimposed on a statistical relationship between the properties of stream catchments and microbial community composition. 4. The catchment regulates microbial communities in two different ways. It harbours the species pool from which the in-stream microbial community is drawn and it governs stream chemistry and the composition of organic substrates that further shape the communities. We suggest that there is a random element to colonisation early in succession, whereas other factors such as species interactions, stream chemistry and organic substrate properties, result in a more deterministic regulation of communities during later stages.

Leaf litter chemistry, decomposition and assimilation by macroinvertebrates in two tropical streams

“…Stream water chemistry is known to directly influence microbial communities in biofilms (Lyautey et al, 2005) and on leaf litter (Fischer et al, 2009). The Fergusson River had higher concentrations of DOC and TDN, conductivity and pH when there was no flow (in July), and combined with the static hydrological conditions, may have led to a divergence in the microbial communities between the rivers.…”

Taxa–area relationship and neutral dynamics influence the diversity of fungal communities on senesced tree leaves

“…Fungal diversity may also be affected by environmental variability in abiotic conditions such as soil moisture. In general, saprotrophic fungal species richness is lower in aquatic habitats than terrestrial habitats (Nikolcheva et al ., 2005; Fischer et al ., 2009; Gessner et al ., 2010). This could be mediated by lower spatial and temporal variation in aquatic habitats, as well as enhanced water‐dependent dispersal among microsites, leading to greater dominance by competitively superior taxa.…”

Rhizosphere disturbance influences fungal colonization and community development on dead fine roots

“…However, several common species emerged in communities, even across multiple study sites, indicating that deterministic factors are of greater importance in the ecology of fine root decay fungi. Fischer et al (2009) showed that initially stochastic processes can give way over time to deterministic effects. Our results differ somewhat from those of Fischer et al (2009), because we did not find evidence for notable changes in community processes over time.…”

“…Fischer et al (2009) showed that initially stochastic processes can give way over time to deterministic effects. Our results differ somewhat from those of Fischer et al (2009), because we did not find evidence for notable changes in community processes over time.…”

“…The importance of chance or random occurrences varies among studies (Sloan et al 2006;Horner-Devine et al 2007;Woodcock et al 2007;Fischer et al 2009), and are of general interest for comparing communities among litter types. The net outcome of these processes is also of functional relevance in fine root substrates, if potential members of the fungal community vary widely in their ability to metabolize plant structural carbon.…”