Empetrum labeling study - R script

· High latitude ecosystems are warming faster than other biomes and are often dominated by a ground layer of Ericaceous shrubs, which can respond positively to warming. The carbon-for-nitrogen (C-for-N) exchange between Ericaceous shrubs and root-associated fungi may underlie shrub responses to warming, but has been understudied.

· In a greenhouse setting, we examined the effects of warming on the C-for-N exchange between the Ericaceous shrub Empetrum nigrum ssp. hermaphroditum and its root-associated fungi. We applied different ¹³C and ¹⁵N isotope labels, including a simple organic N form (glycine) and a complex organic N form (moss litter) and quantified their assimilation into soil, plant biomass, and root fungal biomass pools.

· We found that warming lowered the amount of ¹³C partitioned to root-associated fungi per unit of glycine ¹⁵N assimilated by E. nigrum, but only in the short-term. In contrast, warming increased the amount of ¹³C partitioned to root-associated fungi per unit of moss ¹⁵N assimilated by E. nigrum.

· Our study suggests that climate warming affects the short-term exchange of C and N between a widespread Ericaceous shrub and root-associated fungi. Further, while most isotope tracing studies use labile N sources, we demonstrate that a ubiquitous recalcitrant N source may produce different results.