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SummaryThe concept that ectomycorrhizal plants have a particular foliar trait suite characterized by low foliar nutrients and high leaf mass per unit area (LMA) is widely accepted, but whether this trait suite can be generalized to all ectomycorrhizal clades is unclear.We identified 19 evolutionary clades of ectomycorrhizal plants and used a global leaf traits dataset comprising 11 466 samples across c. 3000 species to test whether there were consistent shifts in leaf nutrients or LMA with the evolution of ectomycorrhiza.There were no consistent effects of ectomycorrhizal status on foliar nutrients or LMA in the 17 ectomycorrhizal/non-ectomycorrhizal pairs for which we had sufficient data, with some ectomycorrhizal groups having higher and other groups lower nutrient status than nonectomycorrhizal contrasts. Controlling for the woodiness of host species did not alter the results.Our findings suggest that the concepts of ectomycorrhizal plant trait suites should be re-examined to ensure that they are broadly reflective of mycorrhizal status across all evolutionary clades, rather than reflecting the traits of a few commonly studied groups, such as the Pinaceae and Fagales.

Ecosystems change between arbuscular mycorrhizal and ectomycorrhizal vegetation dominance over anthropological and geological time scales, yet consequences for ecosystem function are unclear. We review four hypotheses for the effect of mycorrhizal status on ecosystem function. Specifically, that differences between ectomycorrhizal and arbuscular mycorrhizal dominated ecosystems are driven by (1) foliar trait differences, (2) positive plant–soil feedback in ectomycorrhizal plants, (3) differences in the ability to dissolve rocks as a source of nutrition, and (4) differences in the ability to use organic nutrients. We find no universal difference in foliar traits with mycorrhizal status. A spatial simulation suggests that positive plant–soil feedback in ectomycorrhizal plants is unlikely to drive ecosystem differences. However, negative feedback appears to be more common in arbuscular mycorrhizal trees than ectomycorrhizal trees and may represent an important ecosystem difference. Rock dissolution occurs under both mycorrhizal types but may differ in rate. Hypothesis 4 was the best supported: a model and some field evidence suggest that decoupling of carbon and nutrients in ectomycorrhizal decomposition leads to inhibition of saprotrophic mineralization, with context-dependent effects. Greater understanding of organic nutrient utilization differences may be key to improving incorporation of mycorrhizas in ecosystem ecology.

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Ecosystem process rates typically increase after plant invasion, but the extent to which this is driven by (i) changes in productivity, (ii) exotic species’ traits, or (iii) novel (non-coevolved) biotic interactions has never been quantified. We created communities varying in exotic plant dominance, plant traits, soil biota, and invertebrate herbivores and measured indicators of carbon cycling. Interactions with soil biota and herbivores were the strongest drivers of exotic plant effects, particularly on measures of soil carbon turnover. Moreover, plant traits related to growth and nutrient acquisition explained differences in the ways that exotic plants interacted with novel biota compared with natives. We conclude that novel biological interactions with exotic species are a more important driver of ecosystem transformation than was previously recognized.

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