Spring comes early, but do the fungi? Plant phenology mediates plant%u2013fungal interactions under experimental early snowmelt in alpine tundra
Meeder, A., C. P. B. de Mesquita, J. J. Henn, C. Forrester, M. Callaway, S. Schmidt and K. Suding. 2026.
Abstract
Alpine plants experience strong seasonal shifts in resource demand and availability, yet how these
dynamics shape fungal colonization remains unclear. We measured root colonization by arbuscular
mycorrhizal fungi, fine root endophytes, and dark septate endophytes across six alpine plant species at
Niwot Ridge, Colorado, in an early snowmelt simulation experiment and asked how colonization related
to changes in plant phenology and seasonal nutrient context. Using a causal inference, we demonstrate
that fungal colonization was indirectly influenced by early snowmelt through shifts in plant phenology:
plots with later snowmelt timing had later flowering onset and seed set, which in turn supported greater
fungal colonization. Because nutrient measurements were collected in a separate subplot-based data set,
we use them to describe seasonal nutrient context rather than as intermediates in our causal models.
Together, our results identify phenology as the mediator linking snowmelt timing to fungal colonization.
We conclude that climate-driven shifts in snowmelt and reproduction timing can alter when plants
recruit fungal partners: earlier reproduction is associated with reduced colonization if it occurs during
higher nutrient pulses, whereas later reproduction is associated with greater colonization in drier lateseason conditions
Key Words
Snowmelt timing; plant-fungal interactions; mycorrhizae; phenology; causal modeling
