Researchers: Paola Moreno; Marinna Grijalva; Samuel Fitzgerald; Reem Al Dabagh; Stephen Davis; Helen I. Holmlund.
Affiliation(s): Pepperdine University
Summary: Ferns are important players in various ecosystems. For example, they can act as “ecological filters” by influencing establishment of tree seedlings(1). Despite their ecological importance, ferns as a group remain understudied. Most previous fern studies have focused on the life stage known as the sporophyte, a vascular plant with stems, leaves and roots. Most sporophytes have anatomical and physiological features that help regulate water loss, like waxy cuticles which cover the leaf surface and slow epidermal conductance to water vapor. However, little is known about ferns’ other independent life stage, the gametophyte. In contrast to sporophytes, gametophytes are only a single cell layer thick and smaller (<1cm diameter), lacking cuticles or vascular tissue. Since fern gametophytes lack means to slow water loss, it has been hypothesized that many can tolerate and recover from fluctuation of water availability through desiccation tolerance (DT)(2).
DT is defined as a tissue that can dry to equilibrium with moderately dry air and can revive with rehydration (-100 MPa)(3) . There are two different type of DT: constitutive DT and inducible DT. Gametophytes have been hypothesized to be a constitutive DT, meaning that they are able to tolerate rapid drying and will only have minor damages during rehydration(4). However, if in fact gametophytes are inducible DT, they would incur significant damage upon rehydration after rapid drying, and instead they would slow drying in order to recover from desiccation(4). One way to test DT is with dark-adapted chlorophyll fluorescence ( Fv/Fm), which can indicate the maximum quantum yield of photosystem II, which is the marker of chloroplast health. Typically, plants will show decreasing Fv/Fm during drying , but DT plants will recover to their original Fv/Fm during rehydration(5). While some terrestrial fern gametophytes were not DT when desiccated quickly in the lab, we may need field studies to determine whether natural drying speeds result in gametophyte DT.
Soil water potential can indicate the hydration status of the tiny gametophyte, if we assume that the single cell-layered fern gametophyte is in hydraulic equilibrium with the soil. Previous studies have shown a correlation between Fv/Fm and water potential in fern sporophytes during desiccation(5). However, this correlation did not hold during resurrection of DT fern sporophytes because the Fv/Fm recovery lagged behind rehydration(6).
In this study, we examined Fv/Fm and soil water potential in fern gametophytes versus fern sporophytes and fern gametophytes versus moss gametophytes.