Seasonal Photosynthesis, Nitrogen and Phosphorus Dynamics, and Resorption in the Wintergreen Fern Polystichum acrostichoides (Michx.) Schott

Abstract

MINOLETTI, L. M. AND R. E. J. BOERNER. Seasonal photosynthesis, nitrogen and phosphorus dynamics, and resorption in the wintergreen fern Polystichum acrostichoides (Michx.) Schott. Bull. Torrey Bot. Club 120: 397-404. 1993.-Polystichum acrostichoides (Christmas fern) is a widespread and abundant understory plant in deciduous forests of eastern North America. This species has a wintergreen leaf lifespan, in which a cohort of fronds expands in April-May and senesces the following spring as the next frond cohort expands. Because the wintergreen leaf lifespan confers the opportunity for photosynthetic C gain during moderate days in late autumn and winter, we hypothesized that the plant should delay nutrient resorption (retranslocation) from fronds until spring, thus rendering the plant susceptible to overwinter resource loss. We monitored foliar nutrient levels in three cohorts of P. acrostichoides fronds in each of three forest stands which differed in soil fertility, and also made periodic measurements of gas exchange. Polystichum acrostichoides exhibited the capacity for positive net photosynthesis during moderate winter days, with net winter fixation rates similar to those reported for other understory plants during the summer. Foliar N and P concentrations differed significantly among forest sites. Foliar N was highest in plants from the site with the greatest soil N availability but foliar P was not higher at sites with higher P. Nutrient resorption occurred throughout the autumn, winter, and spring, and averaged 54.3% of maximum foliar P and 53.4% of N, with no indication of a significant bias towards autumnal or vernal resorption. N resorption did not differ among sites or correlate well with site fertility; P resorption was greatest in the intermediate fertility site. There was no clear linkage among foliar nutrient concentrations, resorption, winter C gain, and site fertility.