A meta‐analysis of context‐dependency in plant response to inoculation with mycorrhizal fungi

Abstract

Mycorrhizal fungi influence plant growth, local biodiversity and ecosystem function. Effects of the symbiosis on plants span the continuum from mutualism to parasitism. We sought to understand this variation in symbiotic function using meta-analysis with information theory-based model selection to assess the relative importance of factors in five categories: (1) identity of the host plant and its functional characteristics, (2) identity and type of mycorrhizal fungi (arbuscular mycorrhizal vs. ectomycorrhizal), (3) soil fertility, (4) biotic complexity of the soil and (5) experimental location (laboratory vs. field). Across most subsets of the data, host plant functional group and N-fertilization were surprisingly much more important in predicting plant responses to mycorrhizal inoculation (Ôplant responseÕ) than other factors. Non-N-fixing forbs and woody plants and C 4 grasses responded more positively to mycorrhizal inoculation than plants with N-fixing bacterial symbionts and C 3 grasses. In laboratory studies of the arbuscular mycorrhizal symbiosis, plant response was more positive when the soil community was more complex. Univariate analyses supported the hypothesis that plant response is most positive when plants are P-limited rather than N-limited. These results emphasize that mycorrhizal function depends on both abiotic and biotic context, and have implications for plant community theory and restoration ecology.

Plant species differ in their ability to reduce allocation to non‐beneficial arbuscular mycorrhizal fungi

“…However, not all plants appear to be capable of sufficiently reducing allocation to poor mutualists; AMF can parasitize plants (Hoeksema et al 2010), especially in phosphorus-rich environments (Johnson 2010). In this study, I show that plant species differ in the degree to which they adjust allocation to non-beneficial AMF in phosphorus-rich conditions and, accordingly, whether they experience parasitism.…”

“…In this symbiosis, plant response ranges along the mutualism-parasitism continuum (Johnson et al 1997). Plants often benefit from association with arbuscular mycorrhizal fungi (AMF), especially when soil nutrients are scarce (Hoeksema et al 2010). However, when phosphorus is abundant, plants may receive little or no benefit from the symbiosis, so AMF are not plant mutualists and the interaction functions as a commensalism or a parasitism (Johnson et al 1997, Johnson 2010.…”

“…Direct measurement of carbon flux to AMF (Kiers et al 2011) is the ideal indicator of plant allocation; AMF hyphal abundance in the soil, a surrogate for AMF fitness, may also indicate AMF carbon uptake from plants because AMF have no alternative carbon source. Furthermore, reductions in allocation are insufficient to prevent parasitism; parasitism occurred in at least 15% of studies in a meta-analysis of hundreds of mycorrhizal studies (supplement to Hoeksema et al 2010). Why do reductions in carbon allocation so frequently fail to prevent parasitism by AMF?…”

Facilitation between woody and herbaceous plants that associate with arbuscular mycorrhizal fungi in temperate European forests

“…We obtained the most parsimonious model when we fitted Ellenberg N values that reflected site fertility. Both ECM and AM plants are known to be sensitive to high nutrient availability, but this effect appears to be more pronounced for ECM plants (Hoeksema et al., 2010). The positive coefficient (describing a positive relationship) with regard to Ellenberg N indicator values that we found in our most parsimonious path model could arise from the high sensitivity of ECM associations to high site fertility conditions.…”

The extent of mycorrhizal colonization of roots and its influence on plant growth and phosphorus content

“…On average, plants that are colonized by AMF grow 3.1 times larger than do uncolonized control plants (Hoeksema et al 2010). Arbuscular mycorrhizal fungi are thought to be more efficient at scavenging for soil nutrients, owing to their larger surface-to-volume ratios (Sanders and Tinker 1973).…”