Ecotypic differentiation in photosynthesis and growth of Eriophorum vaginatum along a latitudinal gradient in the Arctic tundra

Abstract

Ecotypic differentiation reduces climatic niche breadth at the population level relative to a species' spatial distribution. For species that form climatic ecotypes, if future climate exceeds local population tolerance, climate change will precipitate the decline of extant populations range-wide. Here, we examine the variation in physiological and morphological traits of Eriophorum vaginatum L. collected from a 30-year-old reciprocal transplant experiment, in which six populations of E. vaginatum were transplanted along a latitudinal gradient from Eagle Creek to Prudhoe Bay, Alaska. We tested for ecotypic differentiation of photosynthesis, respiration, chlorophyll fluorescence, and biomass per tiller, which is a metric correlated with population growth in E. vaginatum. The light-saturated photosynthetic rate (A max ) showed homesite advantage in that tussocks in their homesites had significantly higher values of A max relative to nonlocal populations. This pattern of homesite advantage was also observed for biomass per tiller, but not for fluorescence and respiration. Photosynthetic rate was positively correlated with biomass per tiller and survival, suggesting that adaptations related to photosynthesis may optimize performance of local populations to homesite conditions. Taken together, these findings indicate that a rapidly changing climate may elicit population decline of E. vaginatum, rendering this species at a competitive disadvantage to shrubs and boreal forest species, which are expanding northward as the climate changes. Transition from tussock-sedge tundra to boreal forest and shrubland alters features, such as albedo, soil temperature, and water-table depth, in ways that may accelerate climate change.Résumé : La différenciation écotypique réduit l'ampleur de la niche climatique au niveau populationnel relativement à la distribution spatiale d'une espèce. En ce qui concerne les espèces qui forment des écotypes climatiques, si le climat futur excède la tolérance de la population locale, le changement climatique précipitera le déclin des populations qui subsistent sur une large étendue. Les auteurs examinent ici la variation des traits physiologiques et morphologiques d'Eriophorum vaginatum L. récolté dans le cadre d'une expérience de transplantation réciproque pendant 30 ans, dans laquelle six populations d'Eriphorum vaginatum ont été transplantées en fonction d'un gradient latitudinal allant de Eagle Creek à Prudhoe Bay, en Alaska. Les auteurs ont testé la différenciation écotypique de la photosynthèse, de la respiration, la fluorescence de la chlorophylle et la biomasse par talle, une métrique qui est en corrélation avec la croissance de la population chez E. vaginatum. Le taux de photosynthèse en fonction de la densité du flux de lumière (A max ) révélait un avantage de l'habitat d'origine car les buttes gazonnées à leur lieu d'origine présentaient des valeurs d'A max supérieures à celles des populations non locales. Ce patron d'avantage de l'habitat d'origine a aussi été observé sur le plan de la bio...

Biogenic silica accumulation varies across tussock tundra plant functional type

“…We conducted this study on three established research sites (Coldfoot, Toolik Lake, and Sagwon) located along a 300 km north‐south gradient in Alaska (USA) (Souther, Fetcher, Fowler, Shaver, & McGraw, ) (Figure , Table ). Toolik Lake and Sagwon are dominated by classic MAT.…”

Northward displacement of optimal climate conditions for ecotypes ofEriophorum vaginatumL. across a latitudinal gradient inAlaska

“…This integrated metric of season‐long temperature differences was previously shown to be related to both physiological responses (Souther et al ., ) and tiller size (Shaver et al ., ). Mean thaw degree‐days were calculated as the sum of mean air temperatures above 0 °C (Shaver et al ., ), but data for this study were from the SNOTEL weather station nearest to each transplant garden site for the period 2001–2011 (Souther et al ., ), adjusted for elevation differentials using the adiabatic lapse rate. These data were judged likely to be more accurate than the original stripchart data, and their primary purpose was to quantify TDD differences between sites.…”

“…Alternatively, if the original home‐site climate has been displaced northward, or to higher elevations, enhanced fitness might be expected for populations transplanted upward or northward, relative to plants transplanted back to their home sites. We took advantage of a 30‐year‐old Alaskan reciprocal transplant study in which home‐site advantage was previously demonstrated (Shaver et al ., ; Bennington et al ., ) to test whether the optimum environment had indeed shifted northward for genetically distinct populations of a widespread Arctic plant, Eriophorum vaginatum L. A recent analysis of physiological traits of E. vaginatum in the transplant gardens supported the home‐site advantage hypothesis for some traits (e.g., biomass per tiller), but the adaptational lag hypothesis for others (e.g., maximum photosynthetic rate; Souther et al ., ). In this study, we tested the home‐site advantage hypothesis vs. adaptational lag hypothesis using two integrative measures of plant performance: (i) the population growth rate of tillers in the transplanted tussocks and (ii) whole‐tussock survival over the course of the experiment.…”

Future directions and priorities for Arctic bryophyte research

“…Alternatively, diversity may be maintained by ongoing selective processes. A clear understanding of local adaptation in high-latitude plants will also be critical for predicting responses to climate change (Souther et al 2014). If populations are locally adapted, new conditions in a given site are likely to favor alleles that were previously advantageous elsewhere.…”

“…Historically, local adaptation has been detected using reciprocal transplant experiments requiring live material and recurrent visits to experimental study sites (Mooney and Billings 1961;Tieszen and Bonde 1967;McGraw and Antonovics 1983;Shaver et al 1986;Souther et al 2014). More recently, researchers have used trait-based approaches (Q ST -F ST comparisons: Keller et al 2011;QTL analyses: Keller et al 2012;Olson et al 2013) to identify the genetic basis of adaptive differences among populations.…”