Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, SE-90183, Sweden.
International Institute for Applied Systems Analysis, Schlossplatz 1, Laxenburg, A-2361, Austria.
Ecol Lett. 2021 Jun;24(6):1215-1224. doi: 10.1111/ele.13737. Epub 2021 Mar 22.
Trees receive growth-limiting nitrogen from their ectomycorrhizal symbionts, but supplying the fungi with carbon can also cause nitrogen immobilization, which hampers tree growth. We present results from field and greenhouse experiments combined with mathematical modelling, showing that these are not conflicting outcomes. Mycorrhizal networks connect multiple trees, and we modulated C provision by strangling subsets of Pinus sylvestris trees, assuming that carbon supply to fungi was reduced proportionally to the strangled fraction. We conclude that trees gain additional nitrogen at the expense of their neighbours by supplying more carbon to the fungi. But this additional carbon supply aggravates nitrogen limitation via immobilization of the shared fungal biomass. We illustrate the evolutionary underpinnings of this situation by drawing on the analogous tragedy of the commons, where the shared mycorrhizal network is the commons, and explain how rising atmospheric CO may lead to greater nitrogen immobilization in the future.
树木从外生菌根共生体中获得限制生长的氮，但为真菌提供碳也会导致氮固定，从而阻碍树木生长。我们结合田间和温室实验以及数学模型展示了这些结果，表明它们并不是相互矛盾的结果。菌根网络连接着多棵树木，我们通过扼杀部分欧洲赤松来调节 C 的供应，假设向真菌提供的碳供应与被扼杀的部分成比例减少。我们的结论是，树木通过向真菌提供更多的碳，以牺牲邻居为代价获得额外的氮。但是，这种额外的碳供应通过固定共享真菌生物量加剧了氮的限制。我们通过借鉴类似的公共地悲剧来解释这种情况的进化基础，其中共享的菌根网络就是公共地，并解释了为什么大气中 CO 的上升可能会导致未来更多的氮固定。
