A Comparative Ecophysiological Study of Two Fern Species with Contrasting Leaf Morphology (Athyrium filix-femina and Anisocampium niponicum) in the Family Athyriaceae

In a comparative ecophysiological study of two fern species (Athyrium filix-femina and Anisocampium niponicum) growing in the same microenvironmental patch among other ferns on a north facing slope in Palisades, N. Y., the two species had similar maximum photosynthesis rates (3.6 and 3.1 µmol m–2 s–1, respectively), but the light intensity (PPFD) required to reach saturation was somewhat higher for A. niponicum compared to A. filix-femina. The dark respiration rate was higher for samples from A. niponicum (0.54 µmol m–2 s–1) compared to A. filix-femina (0.40 µmol m–2 s–1). Leaf stomatal density expressed as number cm–2 was higher in A. niponicum (4,538) compared to A. filix-femina (2,660), although stomatal size in the two species was fairly similar (c. 48 – 54 µm length and 28 – 30 µm width). The chlorophyll content index (CCI) for A. niponicum was higher (4.72) than A. filix-femina (2.99). Based on leaf fluorescence analysis, Ψo (efficiency with which a trapped exciton can move an electron into the electron transport chain) was higher in A. niponicum (0.73) than A. filix-femina (0.66). The significance of this remains to be determined, but may indicate that higher chlorophyll concentrations correlate to a greater stability of the elevated energy electron (exciton) in PS2 reaction centers due to electron quantum resonance coherence among the light harvesting molecules, and a resulting increased probability that the electron will pass on to the intermediate quinone and beyond in the electron-transport chain.