Abstract Elevated reactive nitrogen deposition can result in declines in belowground C allocation to mycorrhiza, potentially threatening the sustainability of forest ecosystems, especially with regard to ongoing global environmental changes. Previous studies showed that the vulnerability of mycorrhiza differs in different forests. In this paper, we introduce a model that explains such differences as resulting from the optimization of belowground tree C investment in forests with inorganic or organic N economy. According to the model, the optimization of belowground tree C investment in forests with organic N economy is governed by indirect competition between trees for available forms of N. We predict decreasing C investment in mycorrhiza with N deposition in systems dominated by an organic N economy. In contrast, in forests with inorganic N economy the optimization of belowground tree C investment is governed by direct competition between trees for available forms of N. We show that C investment in mycorrhiza does not depend on N deposition in the case of inorganic N economy. Parameterizing the model with data from spruce and beech temperate forests, we show that spruce forests are more sensitive to N deposition with a decrease of tree investment in mycorrhiza, which seems to be consistent with empirical findings. As mycorrhizae are essential for nutrients and water acquisition in trees, we suggest our approach could contribute to predicting the responses of forests to global environmental changes.

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为什么森林对氮沉降的反应不同？建模方法

摘要 活性氮沉降升高会导致菌根的地下碳分配下降，可能威胁森林生态系统的可持续性，尤其是在全球环境持续变化方面。以往的研究表明，菌根的脆弱性在不同的森林中是不同的。在本文中，我们引入了一个模型，该模型解释了由于优化无机或有机氮经济的森林中地下树木 C 投资而导致的差异。根据该模型，有机氮经济森林中地下树木 C 投资的优化受树木之间对可用 N 形式的间接竞争控制。我们预测菌根 C 投资会随着 N 沉积在以有机 N 经济为主的系统中减少。相比之下，在无机氮经济的森林中，地下树木碳投资的优化取决于树木之间对可用氮形式的直接竞争。我们表明，在无机氮经济的情况下，菌根中的碳投资不依赖于氮沉积。使用来自云杉和山毛榉温带森林的数据对模型进行参数化，我们表明，随着树木对菌根的投资减少，云杉林对 N 沉积更敏感，这似乎与实证结果一致。由于菌根对于树木获取养分和水分至关重要，我们建议我们的方法有助于预测森林对全球环境变化的反应。我们表明，在无机氮经济的情况下，菌根的 C 投资不依赖于 N 沉积。使用来自云杉和山毛榉温带森林的数据对模型进行参数化，我们表明，随着树木对菌根的投资减少，云杉林对 N 沉积更敏感，这似乎与实证结果一致。由于菌根对于树木获取养分和水分至关重要，我们建议我们的方法有助于预测森林对全球环境变化的反应。我们表明，在无机氮经济的情况下，菌根的 C 投资不依赖于 N 沉积。使用来自云杉和山毛榉温带森林的数据对模型进行参数化，我们表明，随着树木对菌根的投资减少，云杉林对 N 沉积更敏感，这似乎与实证结果一致。由于菌根对于树木获取养分和水分至关重要，我们建议我们的方法有助于预测森林对全球环境变化的反应。