The carbon balance of boreal terrestrial ecosystems is sensitive to increasing temperature, but the direction and thresholds of responses are uncertain.
Jensen et al. measure seasonal- and cohort-specific photosynthetic temperature response functions in mature black spruce, Picea mariana, in order to model annual cohort carbon uptake under ambient and elevated temperature scenarios. They find that needle cohorts differ in their morphology and photosynthetic capacity, which results in greater annual stand carbon uptake by older needles. Under warmer climate change scenarios, the predicted contribution of young cohorts is even smaller, suggesting that net annual carbon uptake by black spruce could increase under future elevated temperatures, and become more dependent on older needle cohorts.