Rhizosphere Fungal Community Responses to Nitrogen Addition Reflect Genotypic Versus Trait Variation in the Marsh Sedge Schoenoplectus americanus Over Time.

There is growing recognition that shifting environmental conditions can alter the nature and potential benefits of plant-microbe interactions. While it is well established that interactions with fungi can benefit plants under environmental stress, little is known about how plant exposure responses correspond to different factors that might shape fungal communities, particularly over time. Using a resurrection ecology approach, we examined the relative influence of contrasting environmental conditions and intraspecific variation in the foundational marsh sedge Schoenoplectus americanus on rhizosphere fungal communities. Cohorts of ancestral plants germinated from 100+ year old seeds and modern plants were grown under low and high nitrogen (N) concentration in a common-garden experiment. Fungal communities were characterized according to plant presence as well as genotypic and associated trait variation. The study revealed that the influence of S. americanus on fungal communities differed between the nitrogen regimes. Under low N, fungal taxonomic, but not guild, diversity was higher in rhizosphere soils than unplanted controls. Plant effects were, however, diminished under high N conditions. We also found that heritable traits had limited influence on fungal communities, whereas both taxonomic and guild diversity and composition reflected genotypic variation and G × E interactions. Cohorts of ancestral and modern plants also recruited distinct fungal communities depending on N conditions. These results indicate that shifts in plant-fungal associations over time are contingent on prevailing environmental conditions. Our findings also indicate that N-driven changes in plant-fungal interactions likely alter ecosystem processes that are central to saltmarsh resilience to shifting environmental conditions.