White birch has limited phenotypic plasticity to take advantage of increased photoperiods at higher latitudes north of the seed origin

Global warming induced northward migration will expose trees to longer photoperiod regimes during the growing season. The phenotypic ability of trees to take advantage of the longer photoperiods and elevated atmospheric CO2 concentration ([CO2]) will likely be a critical factor for determining their success and performance at the new locations. We investigated how growth, biomass, and biomass allocations respond to the interactive effects of photoperiod regimes and [CO2] in white birch (Betula papyrifera Marsh.). Seedlings were exposed to ambient (400 μmol mol−1) or elevated concentration (1000 μmol mol−1) [CO2], and four photoperiod regimes corresponding to 48 (seed origin), 52, 55, and 58°N latitude for two growing seasons. Our results show that growth, biomass, and biomass allocation were affected by photoperiod regime but not by [CO2]. Seedling growth and biomass were stimulated by the three photoperiod regimes north of the seed origin. Plants under the photoperiod regime of 52°N were 15% higher in growth and 18% higher in biomass than under the photoperiod regime of the seed origin (48°N). However, increases in photoperiod regimes beyond that of 4° north of the seed origin did not lead to an additional increase in growth and biomass. The differences in biomass components among the three longer photoperiods were statistically insignificant, but the leaf biomass and stem biomass were higher under the longer photoperiods relative to the seed origin. While the differences between two adjacent photoperiods were not always statistically significant during the two growing seasons, biomass allocated to roots showed a general decreasing trend with increases in photoperiod from the seed origin to 58°N latitude. Our results suggest that despite the limited plasticity in growth and biomass displayed in much higher latitudes, white birch will likely benefit from the longer photoperiod regimes during the growing season associated with migration or seed transfer to higher latitudes.