Seasonal Movement of Nutrients in Plants of Differing Growth Form in an Alaskan Tundra Ecosystem: Implications for Herbivory

Chapin, F; Johnson, Douglas; McKendrick, Jay

"(1) The seasonal pattern of biomass distribution and of amounts of N, P, K, Ca and Mg was examined in plants of a variety of growth forms in an Alaskan tundra ecosystem. The growth forms examined were: deciduous shrub, evergreen shrub, deciduous forb, tussock graminoid, moss and lichen. (2) The deciduous shrubs Salix pulchra and Betula nana had 70-80% of their biomass below ground, of which about half was roots. The evergreen shrub Ledum palustre had less than 50% of its biomass below ground. (3) In deciduous shrubs, up to 14% of the total plant capital of nitrogen and phosphorus was translocated from stems and large roots into leaves during the 3 weeks following snow-melt. The amount in stems and roots was not fully replaced by uptake until late autumn. At this time, 50-60% of the nitrogen and phosphorus which had been in leaves was removed. In contrast, the evergreen shrub translocated nitrogen and phosphorus to leaves gradually throughout the growing season, and showed no evidence of large stores of nutrients in stems or roots. By late August 46% of the total nitrogen of evergreen shrubs was present in leaves. (4) Potassium was not effectively back-translocated to stems of the deciduous species sampled. (5) In the graminoid Eriophorum vaginatum, spring production of roots as well as leaves depleted nitrogen reserves in the rhizome. Similar dependence of root production upon stored nutrient reserves is suggested in deciduous shrubs. (6) The differences in nutrient allocation between the mosses Aulacomnium spp. and Polytrichum spp. were just as pronounced as those between evergreen and deciduous vascular species, and may relate to the source of nutrients. Lichens had a uniformly low content of the major nutrients. (7) Some implications of seasonal nutrient patterns for herbivores are discussed."

Seasonal Movement of Nutrients in Plants of Differing Growth Form in an Alaskan Tundra Ecosystem: Implications for Herbivory

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