Probing the Panglossian Paradigm: Local Adaptation in Eriophorum vaginatum and its Relation to Functional Traits

Eriophorum vaginatum is a tussock-forming sedge that occupies more than 300 million km² in northern Alaska, Canada, and Siberia. It contributes up to 37% of primary productivity as well as forming the characteristic undulating structure of tussock tundra. Individual tussocks are long-lived, with estimated ages from 122 to 187 years. A series of reciprocal transplant experiments along a latitudinal transect in northern Alaska have demonstrated that populations of E. vaginatum show local adaptation in tiller mass, leaf size and flowering, in that these traits are maximized when tussocks are transplanted back into their sites of origin. Other traits such as tiller population growth rate show evidence of adaptive lag whereby the maximum values for a given population are shifted northwards of the present location of the population, a result that is consistent with the reduced capacity of the locally adapted populations to function in a warming climate. These studies along with genetic evidence indicate that there are two ecotypes of E. vaginatum that are separated at the northern tree line. Differences in phenology appear to be adaptive, with southern populations remaining greener later in the growing season, regardless of where they were planted. On the other hand, many traits including metabolic traits such as J_max, V_cmax, dark respiration, specific leaf area, and leaf nitrogen did not show local adaptation. Such ecotypic variation ecotypic differentiation can affect traits which are important for carbon cycling. Measurements of primary productivity of whole tussocks showed considerable evidence of local adaptation, with the southern ecotype being less productive than the northern ecotypes at all locations, but this was due to variation in canopy and leaf morphology, not photosynthetic rates. Selection for local adaptation may not always produce maximal values for functional traits in long-lived species such as E. vaginatum. The contribution of many traits to fitness may be small and thus not respond significantly to natural selection in the relatively short period following initial colonization of a site. If traits that affect biogeochemical cycles are not optimized rapidly as the climate changes it may reduce the value of optimality for predicting the response of vegetation to global change.