Inconsistent effects of nitrogen canopy enrichment and soil warming on black spruce epiphytic phyllosphere bacterial communities, taxa, and functions

Abstract

Phyllosphere microbial communities have received considerable attention given their important influence on their plant hosts and on ecosystem functioning. In a context where climate change threatens the sustainability of ecosystems, it is important to understand how phyllosphere microbes will respond to changes in their environment. We used 16S rRNA gene amplicon sequencing to quantify phyllosphere bacterial communities of black spruce (Picea mariana (Mill.) B.S.P.) exposed to nitrogen canopy enrichment and soil warming in the boreal forest of Quebec, Canada. The treatments were applied from April to September 2015 and the sampling was done in September. Neither treatment influenced the overall community structure and diversity of black spruce phyllosphere bacterial communities. However, some bacterial taxa and inferred microbial functions did differ among treatments, revealing in particular a stronger response of some bacteria to soil warming rather than nitrogen enrichment. Our results suggest that soil warming could potentially induce more changes in phyllosphere bacterial taxa abundances and functions than could nitrogen addition, with potential consequences for microbial diversity and boreal forest ecosystem function under likely climate change scenarios. Our study suggests avenues for further research to integrate a more mechanistic understanding of the importance of phyllosphere microbes for black spruce and boreal forest ecosystems.