Revisiting mycorrhizal dogmas: Are mycorrhizas really functioning as they are widely believed to do?

Abstract

Since the discovery of mycorrhizas, dogmas have been developed regarding their function, ecology, and distribution. We explore if these dogmas are valid, and if there are research biases toward regions inhabited by most researchers and away from regions inhabited by most plant species. We found, first, that the mycorrhizal status is known in less than 1% of plant species, with few having proven mycorrhizal benefits for growth and development. Second, the mycorrhizal status of a plant species varies within families, even genera. Third, mycorrhizas are important for phosphorus acquisition only within a narrow phosphorus range. Fourth, mycorrhizal plants are not uniform in their response to environment; taxonomy, phylogeny and continental history strongly drive mycorrhizal diversity. For example, the center of diversification of Ericaceae and Orchidaceae is in the neotropics, rather than, as recently claimed, in cold and high-latitude climates. Understanding the importance of mycorrhizas at the family-wide and biome-wide level is therefore conflicted by a research bias toward research-intensive regions outside the phylogenetic hotspots of diversification. The current precepts on mycorrhizas provide important starting points for hypotheses to robustly test when and where mycorrhizas play a role in determining ecological trajectory. The time has come to move forward and revisit past assumptions and update the dogmas, rather than assume functional significance in terms of nutritional benefits from studies on extraneous regions and species. We conclude that non-nutritional benefits deserve far greater attention.

Improved Tolerance of Mycorrhizal Torreya grandis Seedlings to Sulfuric Acid Rain Related to Phosphorus and Zinc Contents in Shoots

“…Notably, in this study, R. irregularis was more efficient at increasing P and Zn 2+ acquisition in T. grandis shoots than other mycorrhizal fungi, which could therefore enhance the yield and nutritional quality of T. grandis nuts in SAR-impacted areas. Numerous studies have confirmed the positive effects of AMF on nutrient uptake and plant quality, which can be considered as an assurance against their deterioration caused by unfavorable factors [ 23 , 57 , 58 ].…”

Mycorrhization of Quercus mongolica seedlings by Tuber melanosporum alters root carbon exudation and rhizosphere bacterial communities

“…Moreover, our current precepts on the function of mycorrhizas are mainly based on assumptions from experimental data of studies using limited species under certain conditions, hereby researchers are encouraged to revisit mycorrhizal dogmas, especially for their non-nutritional bene ts (Albornoz et al 2021). Therefore, ECM-associated C exudation and its effects on soil bacterial structure warrant further study.…”

RUSSELL REVIEW Are plant roots only “in” soil or are they “of” it? Roots, soil formation and function

“…Human activity has had substantial effects on plant N uptake through both the selection of leguminous crops which are estimated to have increased N fixation by 32-53 Tg N/year (Galloway et al, 1995) and the intensification of production systems for food and fibre by the application of about 110 Tg N/year of fertilisers in 2020/21 (IFA, 2020). While the quantity of P fertilisers applied to plants is known (about 17.5 Tg P/year), values for the uptake of P by mycorrhiza are very uncertain because although most vascular plant families can be mycorrhizal, not all species in a family are, and not all mycorrhizal roots are active in P acquisition (Albornoz et al, 2021). In soils with high P status, suppression of AMF has been widely reported so that benefits to crops given P fertiliser are typically small or absent (Ryan & Graham, 2018).…”