Department of Biology, University of Western Ontario, London, ON, Canada.
Nicholas School of the Environment, Duke University, Durham, NC, USA.
Glob Chang Biol. 2016 Aug;22(8):2913-28. doi: 10.1111/gcb.13215. Epub 2016 Mar 8.
Increasing temperatures and atmospheric CO2 concentrations will affect tree carbon fluxes, generating potential feedbacks between forests and the global climate system. We studied how elevated temperatures and CO2 impacted leaf carbon dynamics in Norway spruce (Picea abies), a dominant northern forest species, to improve predictions of future photosynthetic and respiratory fluxes from high-latitude conifers. Seedlings were grown under ambient (AC, c. 435 μmol mol(-1) ) or elevated (EC, 750 μmol mol(-1) ) CO2 concentrations at ambient, +4 °C, or +8 °C growing temperatures. Photosynthetic rates (Asat ) were high in +4 °C/EC seedlings and lowest in +8 °C spruce, implying that moderate, but not extreme, climate change may stimulate carbon uptake. Asat , dark respiration (Rdark ), and light respiration (Rlight ) rates acclimated to temperature, but not CO2 : the thermal optimum of Asat increased, and Rdark and Rlight were suppressed under warming. In all treatments, the Q10 of Rlight (the relative increase in respiration for a 10 °C increase in leaf temperature) was 35% higher than the Q10 of Rdark , so the ratio of Rlight to Rdark increased with rising leaf temperature. However, across all treatments and a range of 10-40 °C leaf temperatures, a consistent relationship between Rlight and Rdark was found, which could be used to model Rlight in future climates. Acclimation reduced daily modeled respiratory losses from warm-grown seedlings by 22-56%. When Rlight was modeled as a constant fraction of Rdark , modeled daily respiratory losses were 11-65% greater than when using measured values of Rlight . Our findings highlight the impact of acclimation to future climates on predictions of carbon uptake and losses in northern trees, in particular the need to model daytime respiratory losses from direct measurements of Rlight or appropriate relationships with Rdark .
升高的温度和大气二氧化碳浓度将影响树木的碳通量，从而在森林和全球气候系统之间产生潜在的反馈。我们研究了升高的温度和二氧化碳如何影响挪威云杉（Picea abies）的叶片碳动态，挪威云杉是北方森林的主要物种，以提高对高纬度针叶树未来光合和呼吸通量的预测。在环境（AC，约 435 μmol mol(-1) ）或升高（EC，750 μmol mol(-1) ）二氧化碳浓度下，幼苗在环境、+4°C 或+8°C 的生长温度下生长。+4°C/EC 幼苗的光合速率（Asat ）较高，而+8°C 云杉的 Asat 最低，这意味着适度但非极端的气候变化可能会刺激碳吸收。Asat 、暗呼吸（Rdark ）和光呼吸（Rlight ）速率适应温度，但不适应 CO2 ：Asat 的热最佳值升高，升温下 Rdark 和 Rlight 受到抑制。在所有处理中，Rlight 的 Q10（叶片温度升高 10°C 时呼吸的相对增加）比 Rdark 的 Q10 高 35%，因此随着叶片温度的升高，Rlight 与 Rdark 的比值增加。然而，在所有处理和 10-40°C 的叶片温度范围内，发现 Rlight 与 Rdark 之间存在一致的关系，这可以用于未来气候模型中的 Rlight 。适应减少了暖生幼苗每天模型化的呼吸损失 22-56%。当将 Rlight 建模为 Rdark 的恒定分数时，模型化的每日呼吸损失比使用 Rlight 的实测值时高出 11-65%。我们的研究结果强调了适应未来气候对北方树木碳吸收和损失预测的影响，特别是需要从 Rlight 的直接测量或与 Rdark 的适当关系来模型化白天的呼吸损失。
