The mycorrhizal-associated nutrient economy (MANE) hypothesis predicts that differences in leaf litter quality between trees associating with arbuscular mycorrhizal (AM) fungi and those associating with ectomycorrhizal (ECM) fungi lead to predictable carbon and nutrient dynamics across diverse forests due to differences in litter decomposition rates. While there is some evidence to support this hypothesis at individual sites, less is known about the generality of MANE. To test this hypothesis, we compiled data on leaf litter chemistry and decay rate (i.e., k values) for > 450 temperate angiosperm tree species. We predicted that variation in AM trees would have greater leaf litter quality and faster litter decomposition rates than ECM trees. Moreover, we expected the largest differences in decay rates to occur in regions with moderate climates where litter quality likely plays a particularly important role in controlling decomposition rates, both directly via energetic and stoichiometric constraints and indirectly by shaping soil nutrient availability and decomposer community composition.
Results/Conclusions
We found AM litter decomposes more quickly than ECM litter across temperate forests (p < 0.001), with this pattern persisting after accounting for climate effects. As is commonly observed, we found a strong relationship between litter chemistry and decomposition rates (p < 0.001), yet litter chemistry did not vary predictably by mycorrhizal group. This decoupling of litter chemistry and mycorrhizal effects on decomposition may be due to nutrient availability and the soil matrix. For example, variation in soil properties under AM versus ECM trees (e.g. differences in nutrient availability, soil moisture and pH, and the decomposer community) are expected to interact with litter quality to control decomposition rates; thus, to the extent to which soil differences vary consistently with mycorrhizal type, soil matrix effects on litter decomposition rates may magnify litter decomposition rate differences between mycorrhizal groups regardless of litter chemistry differences. Nevertheless, these data suggest previously observed differences of litter decomposition rates between AM and ECM trees are universal and provide compelling evidence that a plant’s mycorrhizal association is an important integrative trait linking aboveground plant community composition with forest carbon and nutrient cycling as predicted by the MANE hypothesis.