A comparative ecophysiological study of two forest understory ferns (Dryopteris marginalis and Polystichum acrostichoides) during summer drought and excessive heat

This is a study of the photophysiology of two understory fern species growing on Torrey Cliff, Palisades, N.Y. during the summer of 2022 when the northeast incurred a significant period of drought and elevated temperatures. During the peak period of stress (July and August), mean photosynthesis rates of both species were lower than during more moderate weather in early summer and in autumn. Leaf fluorescence analyses indicated that the mean F v /F m values, combining the data for both species, were fairly similar across the 5 months suggesting that the quantum yield efficiency of photosystem II may be less susceptible to climate stress. However, there was a significant positive correlation between ET 0 /RC values and net photosynthesis rate (r = 0.68, n =10, p = 0.03). This indicates that some of the variation in photosynthesis rates between species across the summer weather pattern may be accounted for by the rate of transfer of electrons from PS II through the intermediate quinone to the site of CO 2 fixation as measured by the ET 0 /RC variable. Dark respiration rates were lower for both species during the most severe heat and drought in July and August.