Edinburgh Napier University

  Arctic ecosystems are under pressure from climate change and atmospheric nitrogen (N) deposition. However, knowledge of the ecology of microbial communities and their responses to such challenges in Arctic tundra soil remain limited, despite the central role these organisms play for ecosystem functioning. We utilised a plot-scale experiment in High Arctic tundra on Svalbard to investigate short-term variation (9 days), following simulation of a N deposition event (4 kg N ha−1 yr−1), in the structure and abundance of bacterial, archaeal and fungal communities between organic and mineral soil horizons. T-RFLP analysis showed significant differences between horizons in bacterial and archaeal community structure. Q-PCR analysis showed that fungal abundance did not differ significantly between soil horizons, whilst bacterial and archaeal abundance was significantly higher in mineral than in organic horizons, despite soil water and total C and N contents being significantly greater in the organic horizon. In the organic horizon, bacterial community structure and fungal abundance varied significantly over time. In the mineral horizon, there was significant variation over time in bacterial abundance, in archaeal community structure and in both fungal community structure and abundance. In contrast, N deposition did not lead to significant variation in either the structure or the abundance of microbial communities. This research demonstrates that microbial community structure and abundance can change rapidly (over only a few days) in Arctic tundra soils and also differently between soil horizons in response to different environmental drivers. Moreover, this variability in microbial community structure and abundance is soil horizon- and taxonomic domain-specific, highlighting the importance of investigating microbial communities across all soil horizons and over short periods of time.