Faster acquisition of symbiotic partner by common mycorrhizal networks in early plant life stage

Arbuscular mycorrhizal (AM) fungi usually improve plant performance yet our knowledge about their effects on seed germination and early plant establishment is very limited. We performed a factorial greenhouse experiment where the seeds from four low Arctic co-occurring mycorrhizal herbs (Antennaria dioica, Campanula rotundifolia, Sibbaldia procumbens, and Solidago virgaurea) were germinated alone or in the vicinity of an adult Sibbaldia plant with or without AM fungi; given either as spores or being present in a common mycorrhizal network (CMN). Three different AM fungal species were examined to assess species-specific differences in symbiont acquisition rate. Of the four plant species investigated, the presence of AM fungi affected seed germination only in Campanula and this effect was dependent on whether the AM fungi were present in the soil as spores or as a CMN. Overall, after germination, developing seedlings showed AM fungal colonization in their roots as soon as 2 d after cotyledon emergence. Our results show that CMN may provide germinating seedlings faster acquisition of the AM fungal partner in comparison to acquisition from spores. Furthermore, there were AM species-specific differences in the symbiont acquisition rate highlighting the importance of species identity in AM interactions. These findings suggest that while AM fungi may not play a fundamental role during seed germination, plant community composition may be affected by the species-specific AM fungal effects on seedling establishment and CMN acquisition.