Arbuscular mycorrhizal fungi change root morphology and nutrient use efficiency in the tree legume Mimosa scabrella

Mimosa scabrella is a leguminous tree native to southern Brazil with high economic potential as a source of timber and biomass. This plant interacts simultaneously with multiple microbial partners in symbiosis, including arbuscular mycorrhizal fungi (AMF). However, the extent of the fungal role and the impact of different AMF species on growth and nutrition remain unclear. This study aimed to evaluate the effects of three AMF species on the growth, nutrient uptake, and root traits of M. scabrella seedlings under varying phosphorus (P) levels. Seedlings were cultivated in a greenhouse for 60 days in sterile sand-soil inoculated with Acaulospora colombiana (AC), A. morrowiae (AM), and Rhizophagus clarus (RC) across five P levels (0; 20; 40; 80; or 160 mg dm⁻³). AMF inoculation strongly enhanced plant growth and nutrient acquisition across P levels, with high levels of mycorrhizal colonization observed even at the highest P concentrations. Biomass production varied among AMF species: AC and RC increased growth 11.6x and 11.7x, respectively, while A. morrowiae promoted a 5.1x increase. Inoculated plants showed reduced specific root length and greater average root diameter (except at 160 mg P dm⁻³), suggesting a potential shift in resource allocation. Concentrations of N, P, and K, as well as nutrient use efficiency (NUE), were consistently elevated in inoculated seedlings, though increases in NUE may partly reflect overall plant size. Despite all AMF species yielding positive results, AC and RC were notably more effective than AM. These findings highlight the importance of considering AMF host preference and local soil conditions in optimizing plant-AMF symbioses. Such optimizations are crucial for enhancing practices in forestry, agriculture, and environmental reclamation. While our results indicate high mycorrhizal responsiveness, the co-inoculation with Burkholderia spp. necessitates caution in inferring true mycorrhizal dependence, and the functional significance of high colonization at elevated P requires further investigation.