The role of ectomycorrhizal fungi in warming-induced regime shift of Arctic tundra
Climate warming is leading shrub expansion in Arctic tundra, but the role of ectomycorrhizal (ECM) fungi in this process is poorly understood. In a series of experiments focused on Betula nana, the dominant shrub increasing in Arctic Alaska, we assessed the effects of warming on the composition of ECM community, and used 13CO2 labelling of plants to elucidate the potential for carbon (C) transfer through ECM networks to be involved in shrub spread. These studies indicated a prominent role for Cortinarius spp. in the response of B. nana to warming and the existence of mycorrhizal networks (MN) involved in inter plant C-transfer. Here, we describe a novel combination of stable isotope probing (SIP) of microbial phospholipid fatty acids (PLFA) and fungal DNA, which we used to identify the ECM fungi involved in C-transfer among B. nana plants in the field.
PLFA-SIP revealed far greater 13C-enrichment of fungal than bacterial PLFAs. Our DNA-SIP-pyrosequencing data indicate that a member of the genus Cortinarius, closely affiliated with C. fennoscandicus, was unique among rhizosphere fungi in being highly enriched in the 13C-SIP-DNA fractions. C. fennoscandicus is considered to be specific to B. nana, consistent with our observation that B. nana was unique among members of this Arctic tundra plant community in it’s ability to transfer C through MNs. Keystone species are those that have disproportionately large impacts on the structure and function of ecosystems relative to their biomass. Our data suggest that C. fennoscandicus may be a keystone species involved in the regime shift of Arctic tundra to shrub tundra as climate warms.