engleski

Fungal‐Bacterial Interplays at Biogeochemical Interfaces: Co‐occurrence of Fungi and Bacteria in Artificial Soils

Contrary to bacteria, mycelial fungi do not rely on continuous water paths during colonization and foraging of spatially heterogeneous biogeochemical interfaces (BGIs) in water unsaturated zones. Thanks to their high surface to volume ratio mycelia take up nutrients and energy sources efficiently, and with hyphal lengths of up to one kilometer per gram soil build up highly complex network structures. Recent studies unraveled that mycelia resemble functional logistic dispersal networks along which bacteria (“fungal highway”) and nutrients and contaminants (“fungal pipeline”) can be transported (Harms et al., 2011). Mycelia may hence also contribute to a BGI‐dependent colonization and the formation of microbial niches in soil. Such knowledge, however, still is sparse. In this study we investigated the impact of four model soil habitats on the development of fungal and bacterial communities and their interplays at BGIs. Four sterile artificial soils were inoculated with a water‐extracted microbial inoculant from an agricultural soil, fertilized with sterile manure and matured for two years. The soils contained quartz sand and silt in combination with (i) montmorillonite, (ii) illite, (iii) montmorillonite and charcoal or (iv) illite and ferrihydrite. After maturation the soils were amended with maize‐potato litter, incubated for another 7, 21 and 63 days and the fungal and bacterial communities analysed with molecular fingerprinting and high‐throughput sequencing. Community structure analyses revealed distinct, BGI‐dependent colonization patterns for the two microbial groups. Soil maturation and the addition of plant litter strongly affected the community composition of the fungi and bacteria with most explicit effect detected in charcoal containing soil. Clearly distinct patterns were also found in response to the type of clay (illite vs. montmorillonite), whereas the ferrihydrite as model metal oxide impacted bacterial communities only. Microbial community network analyses based on Fisher´s exact test further revealed distinct co‐occurrence relationships between fungi and bacteria in response to the composition of the artificial soils (i.e. the abiotic microbial habitat) or the addition of the plant litter. Our data suggest that BGIs are drivers for bacteria and fungi both during colonization of new habitats, as well as their responses to environmental changes, as induced by the addition of plant litter substrates. Combinations of shared niche preferences and helper‐effects (“fungal highways” effect), hence, may explain the soil type dependent community patterns and is currently enlightened via next generation sequencing analysis.

Biogeochemical interfaces ; artificial soils, plant litter ; microbial communities ; co-occurrence

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