Researchers: Samuel Fitzgerald; Marinna Grijalva; Paola Moreno; Reem Al Dabagh; Stephen Davis; Helen I. Holmlund.
Affiliation(s): Pepperdine University
Summary: Ferns, as all plants do, experience life cycles based upon alternation of generations, with the sporophyte of a plant producing haploid spores, those spores growing into gametophytes, and those gametophytes producing the gametes that then fuse and grow into more adult sporophytes. In ferns, the sporophyte is typically regarded as the fern itself, while the gametophytes possess relatively simple, small bodies called thalli, lacking a cuticle or complex vascular structures; ferns exhibit an especially unique form of this life cycle, with their gametophytes and sporophytes living independently from each other.
While the sporophytes demonstrate many unique adaptations that allow their survival in the chaparral1, the gametophytes lack the body structures that would allow them to possess such adaptations. This has prompted our inquiry as to how these cryptic organisms inhabit the same harsh climatic conditions as their sporophyte counterparts. Desiccation tolerance (DT) is an adaptation that allows plants to reach near-total dryness and resurrect upon later rehydration. Little is known about their ecology or habitat8; however, it is thought that desiccation tolerance is the primary lifestyle that these gametophytes exhibit in order to persist through the long, dry summers found in the chaparral.
Desiccation tolerance is characterized by a plant’s vascular tissues being able to dry out completely, reaching water potentials of -100 MPa (most plants have a water potential of -2 MPa), and later being able to resurrect upon rehydration. This lifestyle is thought to be most likely for their survival due to their lack of complex vascular tissues or cuticles to aid in water retention, necessitating survival in a near-absence of water. We observed the fern gametophytes to occupy very specific micro-habitats that provided them with conditions more favorable to their physiology, with gametophyte habitats possessing a narrower temperature range throughout the day and higher relative humidity on average than that of the sporophytes’ habitats. In order to quantify the proposed differences in habitat microclimate, we measured air temperature, leaf temperature, relative humidity, and percent sun, with relative humidity data later being used to calculate the VPD (vapor pressure deficit) of the leaves observed. VPD quantifies the change ambient water undergoes, either via condensation (negative VPD) or evaporation (positive VPD), allowing us to observe the availability of water in the gametophytes’ habitat.