Climate warming is increasing the frequency of climate-induced tree mortality events. While drought combined with heat is considered the primary cause of this mortality, little is known about whether moderately, high temperatures alone can induce mortality, or whether rising CO₂ would prevent mortality at high growth temperatures. We grew tamarack (Larix laricina) under ambient (400 ppm) and elevated (750 ppm) CO₂ concentrations combined with ambient, ambient +4°C, and ambient +8°C growth temperatures to investigate whether high growth temperatures lead to carbon limitations and mortality. Growth at +8°C led to 40% mortality in the ambient CO₂ (8TAC) treatment, but no mortality in the elevated CO₂ treatment. Thermal acclimation of respiration led to similar leaf carbon balances across the warming treatments, despite a lack of photosynthetic acclimation. Photosynthesis was stimulated under elevated CO₂, increasing seedling growth, but not leaf carbon concentrations. However, growth and foliar carbon concentrations were lowest in the +8°C treatments, even with elevated CO₂. Dying 8TAC seedlings had lower needle carbon concentrations and lower ratios of photosynthesis to respiration than healthy 8TAC seedlings, indicating that carbon limitations were likely the cause of seedling mortality under high growth temperatures.

中文翻译：

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变暖和 CO2 升高改变了垂叶草 C 通量、生长和死亡率：在没有水胁迫的情况下与热应激相关的 C 饥饿的证据

气候变暖正在增加气候引起的树木死亡事件的频率。虽然干旱和高温被认为是导致这种死亡的主要原因，但对于仅适度高温是否会导致死亡，或者在高生长温度下升高的 CO ₂是否会防止死亡，我们知之甚少。我们在环境 (400 ppm) 和升高 (750 ppm) CO _{2浓度以及环境、环境 +4°C 和环境 +8°C 生长温度下生长落叶松 (}落叶松)，以研究高生长温度是否会导致碳限制和死亡率。+8°C 的生长导致环境 CO ₂ (8TAC) 处理中 40% 的死亡率，但在升高的 CO _{2中没有死亡率}治疗。尽管缺乏光合适应，但呼吸的热适应导致整个变暖处理过程中的叶片碳平衡相似。光合作用在升高的 CO ₂下受到刺激，增加了幼苗的生长，但不增加叶片的碳浓度。然而，+8°C 处理的生长和叶面碳浓度最低，即使 CO ₂升高。与健康的 8TAC 幼苗相比，垂死的 8TAC 幼苗的针碳浓度和光合作用与呼吸的比率较低，这表明碳限制可能是高生长温度下幼苗死亡的原因。