Ecotypic Differentiation of Growth Processes in Carex Aquatilis along Latitudinal and Local Gradients

The genetic and environmental determinants of plant size, growth rate, reproduction, and survival were examined in five populations of Carex aqualtilis by reciprocal transplants to arctic, subarctic hot spring, subarctic muskeg, temperate alpine, and temperate subalpine sites. In the arctic and muskeg sites, only locally evolved populations survived 3 or more yr. In other sites, interpopulation differences in tiller density were due more to differential autumn or winter mortality than to differences in tillering rate. Shoot height of all populations was smaller when grown in arctic and alpine sites than in others. This small shoot size was genetically fixed in populations native to these sites. In contrast, the muskeg population showed compensatory adaptation to low soil temperature and produced taller shoots than the adjacent hot spring population when both were grown in any given site. All populations maintained similar numbers of green leaves, but through different mechanisms. This occurred through a high leaf production rate in warm soil populations but through enhanced leaf longevity in populations adapted to cold soils. Cold soil populations had larger root: shoot ratios and smaller tiller mass.