Population-level drought responses in northern oak fern (Gymnocarpium dryopteris)

Ferns serve as an invaluable indicator species for soil moisture and distribution patterns of other plant groups. Northern oak fern (Gymnocarpium dryopteris), a common fern in the interior of British Columbia, Canada, has received little research attention despite its prevalent use in the forest resource sector as an indicator species for moisture. To understand the impact of water deficits on oak fern, we sampled in two different ecoregions in interior British Columbia and assessed acclimation to drought, by measuring the size and abundance of stomata in each region. We then subjected the ferns to a period of drought, and recorded the response to stress by measuring the photosynthetic efficiency of the oak fern populations over time. Differences existed in the morphology of oak fern populations; ferns from the wetter ecoregion possessed more, larger stomata then those from the drier ecoregion. Oak ferns from both regional populations were significantly reliant on moisture present in the soil and air to maintain photosynthetic efficiency, and < 20% of the population remained healthy after the 18-day drought period. The stress response of both oak fern populations followed a similar pattern; differences in stomate size and abundance did not result in differences in drought tolerance.