Arctic arbuscular mycorrhizal spore community and viability after storage in cold conditions

Arbuscular mycorrhizal fungi (AMF) form probably the most widespread symbiosis on earth and are found across all ecosystems including the Arctic regions. In the Arctic, the prevalent harsh cold conditions experienced by both host plants and fungi may have selected for AMF species with long-surviving spores, the principal means for dispersal and survival. However, basic knowledge about their viability is lacking. AMF spore assembly from two Arctic sites was examined in soil samples collected across an 11-year period and stored at -20 °C for up to 10 years. AMF spore viability and ability to colonize plants were investigated in the greenhouse using Plantago lanceolata. It was predicted that Arctic AMF spores would survive in cold conditions for several years, with an expected decrease in viability over time as suggested by other experiments with temperate material. Results show that even though the two study sites differed in AMF spore density, the relative abundance of spore morphotypes was rather similar across sites and years. Furthermore, spore viability over time was site-dependent as it decreased only in one site. Although spores were viable, only a very small proportion of hosts and roots became colonized in the greenhouse even 21 months after inoculation. Taken together, these results suggest a certain site-dependent variability in AMF spore communities and the ability of Arctic AMF spores to remain viable after a long-term storage in cold conditions. The lack of host colonization in the greenhouse may be related to the inability to overcome spore dormancy under these conditions.