Onset of autumn senescence in High Arctic plants shows similar patterns in natural and experimental snow depth gradients

Predicted changes in snow cover and temperature raise uncertainties about how the beginning and the end of the growing season will shift for Arctic plants. Snowmelt timing and temperature are known to affect the timing of bud burst, but their effects on autumn senescence are less clear. To address this, researchers have examined senescence under natural and experimental environmental gradients. However, these approaches address different aspects of plant responses and the extent to which they can be compared is poorly understood. In this study, we show that the effect of snowmelt timing on the timing of autumn senescence in High Arctic plants is the same between a natural and an experimental gradient in three out of four studied species. While the two approaches mostly produce comparable results, they give in combination greater insight into the phenological responses to predicted climate changes. We also showed that a short warming treatment in autumn delayed senescence by 3.5 days in D. octopetala, which is a 10 % extension of the growing season end for this species. Warming treatments have commonly been applied to the whole growing season, but here we show that even isolated autumn warming can be sufficient to affect plant senescence.

Interspecific and intraspecific variation in leaf toughness of Arctic plants in relation to habitat and nutrient supply

Leaf toughness is an important functional trait that confers resistance to herbivory and mechanical damage. We sought to determine how species composition, climate, seasonality, and nutrient availability influence leaf toughness in two types of tundra in northern Alaska. We measured leaf toughness as force to punch for 11 species of Arctic plants in tussock tundra and dry heath tundra at 17 sites distributed along a latitudinal gradient. Rubus chamaemorus and the graminoids occupied opposite ends of the leaf toughness spectrum, with R. chamaemorus requiring the least force to punch, while one of the graminoids, Eriophorum vaginatum, required the most. Leaf toughness increased with mean summer temperature for E. vaginatum and Betula nana, while it declined with warmer temperatures for the other species. Toughness of mature leaves of E. vaginatum did not vary through the growing season but declined significantly after senescence. Application of N and P fertilizer in an experimental site decreased leaf toughness in three species but had no effect on four others. Leaf toughness of four out of five species in dry heath was greater than for the same species in tussock tundra, but there was no difference in community-weighted mean toughness between tussock tundra and dry heath.

High Arctic plants show independent responses to pollination and experimental warming

Arctic plants will experience both higher temperatures and changes to their pollination regime under future climate change scenarios. However, reproductive responses to pollination, warming, and a pollination–warming interaction likely vary with seasonal timing in phenology, and may be more pronounced in early-flowering plants than later-flowering plants. To test these hypotheses, we applied hand pollination and exclusion treatments to three Arctic plant species (early-flowering Salix arctica Pall., mid-season flowering Dryas integrifolia Vahl, and late-flowering Papaver radicatum Rottb.) inside and outside of open-top chambers (OTCs), to determine how pollination and warming may interact. We found that OTCs did not significantly reduce visitation by insects, nor did they reduce seed production in wind-pollinated S. arctica. Flower production and seed germination rates for D. integrifolia matched the predictions for warmth- and pollen-limited plants. Reproduction in P. radicatum did not respond strongly to either warming or pollination. Overall, we found that High Arctic plant reproduction is affected independently by pollination and OTC warming, indicating that plant responses to ongoing increases in temperature will not be strongly altered by changes in insect pollination.