Mycorrhizal phosphorus economies: a field test of the MANE framework.

The conquest of the land by plants, c. 470 million years ago, was made possible by the arbuscular mycorrhizal symbiosis (Selosse et al., 2015). In fact, the evolution of that symbiosis was so successful that plant roots have to fit into an arbuscularmycorrhizal world. But that conclusion at the same time hides a paradox. If the arbuscular mycorrhizal symbiosis was so successful, which empty niches (if any!) were left that could subsequently be filled by other mycorrhizal symbioses, particularly the ectomycorrhizal symbiosis? Explaining those unique niches has remained elusive. Several hypotheses have been forwarded, generally based on the idea that the arbuscularmycorrhizal symbiosis plays a larger role in inorganic nutrient (nitrogen (N), phosphorus (P)) cycling, while the ectomycorrhizal symbiosis is more important for organic nutrient cycling (Read & Perez-Moreno, 2003). Recently, Phillips et al. (2013) proposed a conceptual framework, MANE (mycorrhizaassociated nutrient economy), based on the same hypothesis that arbuscular mycorrhizal and ectomycorrhizal trees, not only across but also within biomes, have unique nutrient economies (primary forms of nutrient utilized by mycorrhizal plants and fungi), with ectomycorrhizal trees being characterized by an organic cycle of N and P, and arbuscular mycorrhizal trees by an inorganic cycle of N and P. In this issue of theNew Phytologist, Rosling et al. (pp. 1184– 1195) provide a first field test of the MANE framework for the P cycle, using temperate deciduous forest stands differing in the dominant type of mycorrhizal association.