Divergent arbuscular mycorrhizal growth responses in woody and herbaceous plants across inoculum richness

The mycorrhizal growth response (MGR), defined as the biomass difference between a mycorrhizal plant and a non-mycorrhizal plant of the same species, varies with soil nutrient availability, fungal taxa, and host plant functional group. However, how MGR reacts to changes in arbuscular mycorrhizal fungus (AMF) richness is still not well understood. To assess how AMF richness affected MGR in different organs of plants and discover how MGR varied with plant functional groups, we collected 72 published papers that concurrently studied single and mixed inocula treatments in two common plant functional groups: woody and herbaceous plants. We then compiled a dataset of mycorrhizal colonization rate (MC), MGR of root biomass (MGRr), MGR of shoot biomass (MGRs), MGR of total biomass (MGRt), and root-to-shoot ratio (MGRr/s) for single, dual, and multiple inocula at the fungus and plant species levels. Variation of MGR parameters and MC along inoculum richness generally showed similar patterns at the fungus and plant species levels in both woody and herbaceous plants, respectively. MC tended to increase from single to multiple inocula in the two plant functional groups. MGRs, MGRr, and MGRt tended to increase with increasing inoculum richness in woody plants, but not in herbaceous plants, with nearly 2-fold increments between single and multiple inocula. MGRr/s was generally stable in both woody and herbaceous plants. In general, MC and MGR parameters, except for MGRr/s, were higher in woody plants than in herbaceous plants with the same inoculum richness. The strong positive effect of inoculum richness on MGR parameters in woody plants can be explained by the close relationships between MGR and MC, and between MGR and inoculum richness. Conversely, in herbaceous plants, the associations were weak between MGR parameters and MC or inoculum richness. Our results suggest that multiple inocula generally had a stronger positive impact on MGR parameters than single and dual inocula, and this effect was more prominent in woody plants than in herbaceous plants. These findings not only deepen the understanding of the interaction between AMF richness and host plant growth but also provide insights into the application and development of AMF fertilizer in agriculture and forestry.