DOI: 10.5061/dryad.9ps1n99
title: Data from: Stress‐induced secondary leaves of a boreal deciduous shrub (Vaccinium myrtillus) overwinter then regain activity the following growing season

description: The ericoid shrub Vaccinium myrtillus is one of several deciduous boreal
 plants that respond to larval defoliation by compensatory production of a
 new set of leaves within the same growing season soon after defoliation.
 This new set is termed as ‘secondary leaves’. The physiological
 performance and longevity of secondary leaves is poorly understood.
 Following a multi‐year larval outbreak in boreal Norway, we therefore
 monitored the fate of the secondary leaves from 2014 to 2016. We observed
 that secondary leaves were still green upon onset of snow season and that
 the same leaves were still attached and green when snow melted in spring.
 During the early growing season of 2015, the overwintering leaves were
 consumed by moth larvae, but the secondary leaves produced in mid‐July
 2015 overwintered and were not consumed by larvae the next growing season.
 Our monitoring shows that most of these leaves remained attached until
 late August, while the contents of chlorophyll and nitrogen remained high
 until July. The flavonoid (anthocyanin) content of overwintering leaves
 increased shortly after snowmelt, and this coincided with a short‐lasting
 colour change from green to violet‐bronze. This was probably a protective
 response to the abrupt increase in solar radiation. Overall, secondary,
 overwintering leaves were free of snow and physiologically active for ca.
 6.5 months, which is 2‐3 months more than the longevity of primary leaves
 in the study area. We conclude that wintergreen leaves probably rendered
 an important carbon sequestration contribution in the critical first phase
 of the growing season until new side branches with new leaves were
 developed. Hence, the novel results reported here on the facultative
 wintergreen growth habit of V. myrtillus appears to be a successful
 strategy.
description: Bjerke_et_al_Nord_J_Bot_2018_Fig_2aCharacteristics of shoots with wintergreen leaves measured ca. 5 days after snowmelt in early May 2015: Number of leaves and buds per shoot during May 2015.Bjerke_et_al_Nord_J_Bot_2018_Fig2bCharacteristics of shoots with wintergreen leaves measured ca. 5 days after snowmelt in early May 2015: Contents of chlorophyll (Chl), nitrogen (Nitrogen Balance Index, NBI) and flavonoids (Flav; relative absorbance values)Bjerke_et_al_Nord_J_Bot_2018_Fig_3_overwintering_leavesTemporal changes in contents of chlorophyll concentration (Chl), nitrogen (NBI) and flavonoids (Flav) in wintergreen of Vaccinium myrtillus from snowmelt in early May 2016 to early autumn in late August 2016.Bjerke_et_al_Nord_J_Bot_2018_Fig_3_ new_leavesTemporal changes in contents of chlorophyll concentration (Chl), nitrogen (NBI) and flavonoids (Flav) in new leaves of Vaccinium myrtillus from May 2016 to early autumn in late August 2016.Bjerke_et_al_Nord_J_Bot_2018_Fig_5_leaf colourTemporal changes in frequency of leaf colour state during the 2016 growing season. nm = not measured.Bjerke_et_al_Nord_J_Bot_2018_Fig_6Number of remaining wintergreen leaves per shoot, and number of new side branches per shoot from snowmelt in early May to early autumn in late August 2016. DOY = day of year.