Habitat Distribution And Frond Reorientation As Photoprotection And Drought-Avoidance Mechanisms In Christmas Fern (Polystichum Acrostichoides) In The Southern Appalachian Mountains

ASU Author/Contributor (non-ASU co-authors, if there are any, appear on document)
David Christian Nielsen (Creator)
Appalachian State University (ASU )
Web Site: https://library.appstate.edu/
Howard Neufeld

Abstract: Christmas fern (Polystichum acrostichoides (Michx.) Schott) is a ubiquitous wintergreen herb found in the forests of the Appalachian Mountains, yet it is distributed asymmetrically on the landscape, favoring north-facing slopes and shady stream banks. In late autumn, the fronds of Christmas fern undergo an irreversible reorientation, bending at the base of the stipe and lying flat on the forest floor. These fronds maintain high chlorophyll concentrations throughout winter and are photosynthetically active on warm winter days and in early spring before canopy emergence. In three populations in the Appalachian State University Biological Preserve, I prevented fronds from reorienting using wooden dowels and floral wire, artificially holding them up over winter. The fronds that were prevented from reorienting to a prostrate position suffered severe photoinhibition characterized by extensive leaf necrosis coupled with significant declines in light-saturated gas exchange, chlorophyll fluorescence (Fv/Fm), and total chlorophyll, while a control group showed little or no declines as winter progressed. “Surrogate ferns” were constructed and mounted with light sensors in order to characterize the light environment at the leaf level on north- and south- facing slopes. Inclined fronds experienced much higher light levels than prostrate fronds (oriented horizontally), on both slopes, and the sensor on the south-facing slope experienced 22 days in which light exceeded 500 µmol m-2 s-1 and the air temperature at the leaf level was below freezing. Conversely, on the north-facing slope, these conditions only occurred on one day. This result suggests that frond reorientation is sufficient to prevent photoinhibition in overwintering fronds of Christmas fern by reducing winter light, and may be a significant factor limiting its distribution on south-facing slopes where it is bright and cold during winter. Christmas ferns demonstrated remarkable resilience in a controlled dry-down, with little physiological decline as midday water potentials exceeded -1.0 MPa and soil water content approached 0%. Presently, it is unclear how fern water relations contribute to frond reorientation or distribution on the landscape, but the microclimate data suggest that south- facing slopes are not dry enough to induce significant physiological stress on Christmas fern, and that winter light may have more influence. Forecasted changes in local climate may alter the range and distribution of Christmas fern. Our results provide insight into how this species might be affected, with significant ecological implications for understory herbs in our region.

Additional Information

Nielsen, D. (2017). "Habitat Distribution And Frond Reorientation As Photoprotection And Drought-Avoidance Mechanisms In Christmas Fern (Polystichum Acrostichoides) In The Southern Appalachian Mountains." Unpublished Master’s Thesis. Appalachian State University, Boone, NC.
Language: English
Date: 2017
christmas fern (polysticum acrostichoides), ecophysiology, climate change, aspect and microclimate, university biological/ nature preserve

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