• Efforts to develop mechanistic tree growth models are hindered by the uncertainty of whether and when tree growth responses to environmental factors are driven by carbon assimilation or by biophysical limitations of wood formation.
• In this study, we used multiannual weekly wood‐formation monitoring of two conifer species (Larix decidua and Picea abies) along a 900 m elevational gradient in the Swiss Alps to assess the biophysical effect of temperature and water potential on wood formation. To this end, we developed a model that simulates the effect of water potential on turgor‐driven cambial division, modulated by the effect of temperature on enzymatic activity.
• The model reproduced the observed phenology of tracheid production, as well as intra‐ and interannual tracheid production dynamics of both species along the elevational gradient, although interannual model performance was lower. We found that temperature alone explains the onset of tracheid production, yet water potential appears necessary to predict the ending and the total amount of tracheids produced annually.
• We conclude that intra‐annual cambial activity is strongly constrained by both temperature and water potential at all elevations, independently of carbon assimilation. At the interannual scale, biophysical constraints likely interact with other factors.

中文翻译：

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温度和水势共同限制沿陡峭海拔梯度的茎类活动

• 树木生长对环境因素的响应是否以及何时受到碳同化或木材形成的生物物理限制的不确定性阻碍了开发机械树木生长模型的努力。
• 在这项研究中，我们在瑞士阿尔卑斯山沿900 m海拔梯度对两个针叶树种（落叶松和云杉）进行了每周一次的木材形成监测，以评估温度和水势对木材形成的生物物理影响。为此，我们开发了一个模型，该模型可模拟温度对酶促活性的影响，从而调节水势对膨大驱动的冈比亚分裂的影响。
• 该模型再现了观察到的气管生产的物候学特征，以及沿海拔高度梯度的两个物种的年内和年内气管生产动态，尽管年间模型的性能较低。我们发现，温度本身可以解释气管生产的开始，但是水势似乎是预测年产量和总数量的必要条件。
• 我们得出的结论是，年内的冈比亚活动在所有海拔高度都受到温度和水势的强烈限制，而与碳同化无关。在年际尺度上，生物物理限制可能与其他因素相互作用。