Organic matter quantity and source affects microbial community structure and function following volcanic eruption on Kasatochi Island, Alaska

Lydia H. Zeglin, Bronwen Wang, Christopher Waythomas, Frederick Rainey, Sandra L. Talbot

In August 2008, Kasatochi volcano erupted and buried a small island in pyroclastic deposits and fine ash; since then, microbes, plants and birds have begun to recolonize the initially sterile surface. Five years post-eruption, bacterial 16S rRNA gene and fungal ITS copy numbers and extracellular enzyme activity potentials (EEAs) were one to two orders of magnitude greater in pyroclastic materials with organic matter (OM) inputs relative to those without, despite negligible accumulation of OM (< 0.2 %C). When normalized by OM levels, post-eruptive surfaces with OM inputs had the highest β-glucosidase, phosphatase, NAGase and cellobiohydrolase activities, and had microbial population sizes approaching those in reference soils. In contrast, the strongest factor determining bacterial community composition was the dominance of plants versus birds as OM input vectors. While soil pH ranged from 3.9-7.0, and %C ranged 100x, differentiation between plant- and bird-associated microbial communities suggested that cell dispersal or nutrient availability are more likely drivers of assembly than pH or OM content. This study exemplifies the complex relationship between microbial cell dispersal, soil geochemistry, and microbial structure and function, and illustrates the potential for soil microbiota to be resilient to disturbance.