Variation in white spruce needle respiration across the species range

Abstract

White spruce (Picea glauca) spans a massive range from arctic treeline to temperate forests. Yet the variability in respiratory physiology and the implications for tree carbon balance at the extremes of this distribution remain enigmasWorking at Arctic and Temperate sites more than 5000 km apart, we measured the short-term temperature response of dark respiration (R/T) at upper and lower canopy positions. R/T curves were fit to a polynomial model and model parameters (a, b, and c) were compared between locations, canopy positions, or with published data. Respiration measured at 25°C (R25) was 68% lower at the southern location than the northern location, resulting in a significantly lower a parameter of the R/T response in temperate trees Only at the southern location did upper canopy leaves have a steeper temperature response than lower canopy leaves, likely reflecting steeper canopy gradients in light. No differences were manifest in the maximum temperature of respiration. At the northern range limit, respiration appears extreme. This high carbon cost likely contributes to the current location of northern treeline. We find that respiration will increase with end-of-the-century warming and will likely continue to constrain the future range limits of this important boreal species. Summary Statement White spruce (Picea glauca) needle respiration at the northern limit of the species range is three times higher than at the southern range limit. This extreme carbon cost likely challenges tree survival and contributes to the location of the northern treeline.