Seasonal patterns of photosynthesis and nutrient storage in Eriophorum vaginatum L., an arctic sedge

Maximum photosynthetic rates of Eriophorum vaginatum L. growing in the field in interior Alaska followed a seasonal pattern similar to those of air temperature, nitrogen and chlorophyll, being lowest at snow melt, increasing sharply in summer and declining in autumn. Total photosynthetic potential per tiller reached 80% of the seasonal maximum within 3 weeks of snow melt, enabling plants to exploit the long photoperiod and high irradiance that characterize early summer. New leaves gradually replaced over-wintering leaves as the major source of photosynthate as a result of sequential leaf development. Nitrogen and phosphorus were stored over winter in rhizomes primarily as arginine, glutamine, asparagine and alanine, and as an unidentified soluble organic phosphate, respectively. Rhizome nutrient stores declined in spring coincident with the increase in photosynthetic potential of shoots. Then, in the latter half of the growing season, accumulation of rhizome reserves coincided with the decline in shoot nitrogen and photosynthetic potential. We conclude that the seasonal development of photosynthetic capacity in E. vaginatum requires the sequential pattern of leaf production and senescence as modified by seasonal flux of nutrients into or out of rhizomes. The similarity of seasonal patterns of air temperature and photosynthetic potential suggests that temperature acclimation may also be an important determinant of photosynthetic potential.