Senescence of arctic plants under conditions of altered seasonality

Background/Question/Methods

Warming temperatures at northern latitudes are extending the period of favorable conditions for plant growth. Earlier snowmelt and later snowfall are occurring, but to what extent will plant species take advantage of extension in the snow-free season? Across northern latitudes, the timing of leafing and flowering is occurring earlier due to warming, but controls on of end-of-season phenology are less well understood. Changes in both start- and end-of-season phenology affect species’ active and reproductive periods. We examined the effect of altering key environmental drivers of phenology (timing of snowmelt and temperature) on the active and reproductive periods of plants in a moist acidic tundra. Snowmelt was accelerated using black shadecloth placed over the snowpack and air temperature increased through passive open-top warming chambers. We hypothesized that senescence of Arctic plant species would either 1) advance concurrent with timing of start of season phenology due to periodic constraints on growth, 2) advance independent of start of season phenology due to environmental stresses such as reduced soil moisture or increased soil temperature, 3) stay the same among years and treatments due to strong internal controls, or 4) be delayed by favorable growth conditions and a lack of internal controls.  

Results/Conclusions

Warming and early snowmelt treatments increased soil temperature and reduced soil moisture throughout the season. The combined treatments resulted in the greatest increase in soil temperature and the greatest reduction in soil moisture. Interannual variation in senescence for deciduous shrub and graminoid species indicates that photoperiod is not the sole control of senescence for these species. Evergreen shrubs showed less variation in senescence between years, indicating that photoperiod or periodic constraints may play a more important role. Within a given year, species had differing responses to early snowmelt and warming treatments. For example, E. vaginatum and S. pulchra showed little to no change in timing among treatments, while B. nana and C. bigelowii senesced earlier. However, the direction and magnitude of response varied among years.  Our results highlight the complex nature of senescence processes under altered environmental conditions.