Forest trees are able to thrive in nutrient-poor soils in part because they obtain growth-limiting nutrients, especially nitrogen (N), through mutualistic symbiosis with ectomycorrhizal (ECM) fungi. Addition of inorganic N into these soils is known to disrupt this mutualism and reduce the diversity of ECM fungi. Despite its ecological impact, the mechanisms governing the observed effects of elevated inorganic N on mycorrhizal communities remain unknown. We address this by using a compartmentalized in vitro system to independently alter nutrients to each symbiont. Using stable isotopes, we traced the nutrient flux under different nutrient regimes between Eucalyptus grandis and its ectomycorrhizal symbiont, Pisolithus albus. We demonstrate that giving E. grandis independent access to N causes a significant reduction in root colonization by P. albus. Transcriptional analysis suggests that the observed reduction in colonization may be caused, in part, by altered transcription of microbe perception genes and defence genes. We show that delivery of N to host leaves is not increased by host nutrient deficiency but by fungal nutrient availability instead. Overall, this advances our understanding of the effects of N fertilization on ECM fungi and the factors governing nutrient transfer in the E. grandis-P. microcarpus interaction.

中文翻译：

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无机氮的利用会改变桉树对外生菌根真菌Pisolithus albus的接受性，但不会改变共生氮的转移。

林木之所以能够在营养贫瘠的土壤中繁衍生息，部分原因是它们通过与外生菌根（ECM）真菌的共生共生获得了限制生长的营养素，尤其是氮（N）。已知在这些土壤中添加无机氮会破坏这种共存关系，并降低ECM真菌的多样性。尽管其对生态有影响，但支配观察到的升高的无机氮对菌根群落影响的控制机制仍然未知。我们通过使用隔离的体外系统独立地改变每个共生体的营养来解决这个问题。使用稳定的同位素，我们追踪了桉树及其外生菌根共生体Pisolithus albus在不同养分制度下的养分通量。我们证明给予大肠埃希斯独立访问N会导致由白假单胞菌根定植显着减少。转录分析表明，观察到的定植减少可能部分是由于微生物感知基因和防御基因的转录改变所致。我们表明，氮向寄主叶片的输送不会因寄主营养缺乏而增加，而是由真菌营养的可获得性增加。总的来说，这提高了我们对氮肥对ECM真菌的影响以及在E. grandis-P中控制养分转移的因素的理解。微果皮相互作用。这使我们进一步了解了氮肥对ECM真菌的影响以及在E. grandis-P中控制养分转移的因素。微果皮相互作用。这使我们进一步了解了氮肥对ECM真菌的影响以及在E. grandis-P中控制养分转移的因素。微果皮相互作用。