Arbuscular mycorrhizal fungal genotype and nuclear organization as driving factors in host plant nutrient acquisition and stable carbon storage

Summary

• Arbuscular mycorrhizal fungi (AMF) are obligate root symbionts of most plants that improve plant growth by transferring nutrients into plant roots through networks of soil hyphae. These hyphal networks represent a carbon sink in soil; thus, it has been suggested that these fungi can also boost atmospheric carbon storage, highlighting their potential role in managing greenhouse emissions. In this study, we aimed to determine whether certain AMF genotypes and nuclear organizations (homokaryons vs heterokaryons) are associated with higher rates of host plant yield and carbon storage.

• We compared Sudan-grass (Sorghum × drummondii) AMF inoculation across eight strains of Rhizophagus irregularis: four homokaryotic and four heterokaryotic strains. Sudan-grass was grown in a growth chamber, which included ¹³C-CO₂ pulse labeling to track plant carbon into AMF.

• AMF inoculation increased total and belowground biomass, as well as phosphorous, magnesium, and manganese uptake in the host. Heterokaryons led to greater belowground biomass, as well as less variable increases in shoot phosphorous. Mycorrhizal inputs to soil mineral-associated organic carbon − a highly persistent carbon pool with slow turnover − were overall greater in heterokaryons than in homokaryons but varied significantly among strains.

• This indicates that the potential for carbon storage by mycorrhizal carbon inputs varies based on fungal genomic identity and nuclear organization. Overall, inoculation improved the yield of Sudan-grass and resulted in significant inter-strain variation in persistent carbon contributions to the soil. This work highlights the importance of considering genotype and nuclear identity in assessments of AMF as bio-stimulants and drivers of carbon storage.