Format: ORAL

Kathrin Rousk

Department of Biology, Center for Volatile Interactions, VOLT, University of Copenhagen Copenhagen, Denmark

Nitrogen (N) fixation by moss-associated cyanobacteria is the main source of new N in pristine ecosystems such as arctic tundra, boreal forests, and tropical cloud forests. While we have a good understanding of individual factors (e.g. temperature, humidity) that drive this ecosystem process, we still lack a comprehensive framework that can answer key questions in biogeochemistry, symbioses and ecophysiology research. Here, I will present N fixation data from various environmental gradients (and thereby the combined effects of various factors), ranging from altitudinal to nutrient availability gradients, as well as moss hosts to synthesize current knowledge on moss-associated N fixation. For instance, N fixation decreased with elevation along a tropical forest mountain, linked to sharp declines in air temperature, relative humidity as well as shifts in bacterial communities associated with mosses. Nitrogen availability or pollution is another key driver of moss-associated N fixation, with inhibiting effects along natural N fertility gradients as well as in laboratory settings. In contrast, heavy metal pollution seems to be less detrimental. Whether moss host or the habitat drives bacterial communities on mosses, and thereby, N fixation rates, is an ongoing debate, and I will bring new data to the debate.