Germination and epiphytic seed fungi on Festuca roemeri and Danthonia californica

Demographic studies measure drivers of plant fecundity such as seed
production and survival, but few address environmental drivers of seed
viability, such as germination and dormancy. Variation in climate and seed
type may both directly and indirectly alter seed germination via altered
fungal pathogen abundance. We examined seed germination and microbial
communities of seeds of Danthonia californica, which are either
chasmogamous (external, wind-pollinated) or cleistogamous (internal,
self-fertilized) and Festuca roemeri, which are solely chasmogamous. Seed
populations were sourced across environmental gradients. We tested
germination and characterized seed fungal community structure, using
high-throughput sequencing. For F. roemeri, maternal plant significantly
influenced germination as did climate and pathogens; germination increased
in wetter, cooler sites. For D. californica, the main drivers of
germination were maternal plant, seed type and pathogens; on average, more
chasmogamous seeds germinated. Fungal composition depended on seed type,
with fewer fungi associated with cleistogamous seeds. Seed fungal
composition varied with climate, plant density and mean proportion of
seeds germinated. Putative pathogens that were negatively correlated with
germination were more abundant for both Danthonia and Festuca chasmogamous
seeds than Danthonia cleistogamous seeds. In D. californica, cleistogamous
and chasmogamous seeds contain vastly different fungal communities.