Ecotypic Differentiation in Carex Aquatilis on Ice-Wedge Polygons in the Alaskan Coastal Tundra

Abstract

(1) Growth and nutrient relations of Carex aquatilis were examined in the field and in glasshouse-grown plants from five polygon microhabitats in wet meadow tundra at Barrow, Alaska. These habitats can occur within 1 m of each other, and differ greatly in soil moisture, availability of N and P and thaw depth. (2) Field-grown plants from these microhabitats differed between populations in above-ground weight per tiller, leaf-production rate, root:leaf weight ratio, rate of uptake of 32P, and concentration of sugar, N and P in roots and rhizomes. Tissue concentrations of N and P were correlated with corresponding availability in the soil but not with plant size. There was a moderate positive correlation between soil moisture and plant size. (3) Carex aquatilis populations grown in the glasshouse with either no addition or moderate addition of phosphate showed no significant differences in plant size, but large differences in tissue-nutrient concentrations, 32P-uptake kinetics and responsiveness to phosphorus availability. A strong effect of phosphorus stress on nitrogen and potassium metabolism was observed. Responsiveness of 32P-uptake kinetics to changed conditions was inversely related to the degree of responsiveness in growth rate and mineral accumulation in the tissues. (4) These ecotypic differences among populations of Carex aquatilis are remarkable in view of the extreme rarity of reproduction by seed in the field, and the close proximity of the populations.