With the recent climate warming, tundra ecotones are facing a progressive acceleration
of spring snowpack melting and extension of the growing season, with evident
consequences to vegetation. Along with summer temperature, winter precipitation has
been recently recognised as a crucial factor for tundra shrub growth and physiology.
However, gaps of knowledge still exist on long-living plant responses to different
snowpack duration, especially on how intra-specific and year-to-year variability together
with multiple functional trait adjustments could influence the long-term responses.
To fill this gap, we conducted a 3 years snow manipulation experiment above the
Alpine treeline on the typical tundra species Juniperus communis, the conifer with the
widest distributional range in the north emisphere. We tested shoot elongation, leaf
area, stomatal density, leaf dry weight and leaf non-structural carbohydrate content of
plants subjected to anticipated, natural and postponed snowpack duration. Anticipated
snowpack melting enhanced new shoot elongation and increased stomatal density.
However, plants under prolonged snow cover seemed to compensate for the shorter
growing period, likely increasing carbon allocation to growth. In fact, these latter showed
larger needles and low starch content at the beginning of the growing season. Variability
between treatments slightly decreased over time, suggesting a progressive acclimation
of juniper to new conditions. In the context of future warming scenarios, our results
support the hypothesis of shrub biomass increase within the tundra biome. Yet, the
picture is still far from being complete and further research should focus on transient
and fading effects of changing conditions in the long term.
