We present a mechanistic model of coexistence among a mycorrhizal fungus and one or two plant species that compete for a single nutrient. Plant–fungal coexistence is more likely if the fungus is better at extracting the environmental nutrient than the plant and the fungus acquires carbon from the plant above a minimum rate. When they coexist, their interaction can shift from mutualistic to parasitic at high nutrient availability. The fungus is a second nutrient source for plants and can promote the coexistence of two plant competitors if one is better at environmental nutrient extraction and the other is better at acquiring the nutrient from the fungus. Because it extracts carbon from both plants, the fungus also serves as a conduit of apparent competition between the plants. Consequently, the plant with the lower environmental nutrient extraction rate can drive the plant with the higher environmental nutrient extraction rate extinct at high carbon supply rates. This model illustrates mechanisms to explain several observed patterns, including shifts in plant–mycorrhizal growth responses and coexistence along nutrient gradients, equivocal results among experiments testing the effect of mycorrhizal fungi on plant diversity, and differences in plant diversity among ecosystems dominated by different mycorrhizal groups.

中文翻译：

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决定植物和菌根真菌共存的相互作用的复杂电路

我们提出了一种菌根真菌和一种或两种竞争单一营养物质的植物物种共存的机制模型。如果真菌比植物更善于提取环境养分，并且真菌从植物中获取的碳高于最低速率，那么植物与真菌共存的可能性就更大。当它们共存时，在高营养可用性的情况下，它们的相互作用可以从共生转变为寄生。真菌是植物的第二营养源，如果一种植物更擅长提取环境养分，另一种更擅长从真菌中获取养分，则可以促进两种植物竞争者的共存。由于它从两种植物中提取碳，因此真菌也成为植物之间明显竞争的渠道。因此，具有较低环境养分提取率的植物可以在高碳供应率下驱动具有较高环境养分提取率的植物灭绝。该模型阐明了解释几种观察到的模式的机制，包括植物-菌根生长反应的变化和沿营养梯度的共存、测试菌根真菌对植物多样性影响的实验中的模棱两可的结果，以及不同菌根类群主导的生态系统中植物多样性的差异。