SEASONAL PHOTOSYNTHESIS, NITROGEN AND PHOSPHORUS DYNAMICS, AND RESORPTION IN THE WINTERGREEN FERN POLYSTICHUM-ACROSTICHOIDES (MICHX) SCHOTT

Polystichum acrostichoides (Christmas fem) is a widespread and abundan t 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 fro nd cohort expands. Because the wintergreen leaf lifespan confers the o pportunity for photosynthetic C gain during moderate days in late autu mn and winter, we hypothesized that the plant should delay nutrient re sorption (retranslocation) from fronds until spring, thus rendering th e plant susceptible to overwinter resource loss. We monitored foliar n utrient levels in three cohorts of P. acrostichoides fronds in each of three forest stands which differed in soil fertility, and also made p eriodic measurements of gas exchange. Polystichum acrostichoides exhib ited the capacity for positive net photosynthesis during moderate wint er days, with net winter fixation rates similar to those reported for other understory plants during the summer. Foliar N and P concentratio ns 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 maxim um foliar P and 53.4% of N, with no indication of a significant bias t owards autumnal or vernal resorption. N resorption did not differ amon g sites or correlate well with site fertility; P resorption was greate st in the intermediate fertility site. There was no clear linkage amon g foliar nutrient concentrations, resorption, winter C gain, and site fertility.