Vascular plants regulate responses of boreal peatland Sphagnum to climate warming and nitrogen addition.

Boreal peatland Sphagnum may be affected by climate warming and elevated nitrogen availability directly and indirectly via altering vascular plant interaction. Here, we used a field experiment of nitrogen addition, warming, and vascular plant removal to investigate the effects of these factors on Sphagnum in a Canadian blanket boreal peatland. We revealed that significant effects of warming and nitrogen addition on Sphagnum were regulated by vascular plant interaction. The intense competition of vascular plants accelerated an adverse effect of warming on Sphagnum, while facilitation of vascular plants reduced detrimental losses of the Sphagnum due to high dose of nitrogen addition and both warming and the nitrogen addition. These findings indicate the crucial role of vascular plants in regulating the effects of environmental changes on existing Sphagnum in boreal peatlands.