Revisiting root morphological responses to arbuscular mycorrhizal fungal inoculation (AMF): a global meta-analysis

Arbuscular mycorrhizal fungi (AMF) contribute to plant resource acquisition and stress tolerance. Although individual studies suggest AMF can modify root morphology, it remains unclear whether these effects are consistent across species. Previous meta-analyses have focused on the impact of AMF inoculation on plant biomass, nutrient uptake/concentration, or stress alleviation, but root response has remained unclear. To address this, we conducted a global meta-analysis of 269 trials from 61 studies to quantify AMF inoculation effects on fine root morphological traits in non-woody plants and evaluated seven moderator variables spanning host plant (family, functional type), fungal (guild, inoculation type), environmental (stress conditions), and experimental (setting, duration) contexts. Overall, AMF inoculation significantly increased root surface area (40%), root length (30%), average root diameter (10%), root dry weight (59%), root fresh weight (48%), and root branching (18%), whereas root tissue density (RTD), specific root area (SRA), and specific root length (SRL) showed no significant response. Root responses were context-dependent, with host plant families as the primary driver. SRL declined in Asteraceae and Fabaceae but increased strongly in Malvaceae, while root surface area and root length increased in Asteraceae, and Fabaceae showed a weaker response. Furthermore, stress and experimental duration influenced root dry weight, root surface area, and root length, whilst plant functional type, AMF inoculum type, and AMF guild were not strong moderators. These findings highlight that AMF generally promote root system expansion without altering root construction strategies, highlighting host taxonomic identity as the dominant factor shaping root trait responses.