Does herbivory really suppress mycorrhiza? A meta‐analysis

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Abstract
Summary: 1. aged and natural ecosystems, herbivory can have a major impact on plant growth. Defoliation and shoot removal reduce the photosynthetic capacity of plants and are also thought to reduce allocation of carbon to roots and mycorrhizal fungi. However, evidence supporting this assumption remains equivocal. 2. ducted a meta‐analysis of 99 experiments, from 33 publications, measuring arbuscular and ectomycorrhizal colonization of roots after real or simulated herbivory removed leaves or shoots. We also explored how effects were moderated by the type of mycorrhiza, fertilization, experimental setting (laboratory or field), treatment (real herbivory of shoots, real herbivory of leaves, simulated herbivory of shoots, simulated herbivory of leaves), type of host plant, duration of the experiment and year of publication. 3. Overall, herbivory reduced mycorrhizal colonization by about 3 percentage points. Treatment, host plant type and year of publication were the only significant moderators, with real or simulated herbivory of leaves and real herbivory of shoots suppressing colonization, while simulated removal of shoots tended to increase colonization. Herbivory reduced colonization of perennial grasses and deciduous trees by about 4 and 8 percentage points, respectively. Mycorrhizal colonization of annual crops was reduced by about 12 percentage points, although this was not significantly different from zero. Mycorrhizal colonization of perennial forbs and evergreen trees was also unaffected by herbivory, and colonization of mixtures of perennial grasses and forbs increased by about 15 percentage points following herbivory. Effect size increased with year of publication, likely due to shifts in experimental designs towards systems more likely to show positive effects of herbivory on mycorrhiza. 4. Synthesis. Our results challenge the carbon‐limitation hypothesis and suggest that herbivory, real or simulated, reduces mycorrhizal colonization by biologically meaningful amounts only in a limited subset of systems.

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