MYCOLab Ai Logo - gold and army green

Root anatomy governs bi-directional resource transfer in mycorrhizal symbiosis

Summary

Researchers developed a new theory explaining how plant roots and fungi work together to exchange nutrients and carbon. The theory shows that thicker roots are less efficient at absorbing nutrients on their own, but mycorrhizal fungi help by positioning themselves in the inner layers of roots to reduce the energy cost of nutrient transport. This partnership between roots and fungi becomes increasingly important for thicker roots, explaining why many plants with thick roots depend more heavily on fungal partners for survival.

Background

Plants form mycorrhizal symbioses to enhance nutrient acquisition, but the biophysical principles governing carbon and nutrient exchange remain unclear. Root anatomical allometry—where tissues outside the stele (ToS) increase more steeply than stele radius with increasing root diameter—is a globally occurring phenomenon fundamental to understanding root form and function.

Objective

To develop a biophysical theory integrating root anatomy, energetic costs, and mycorrhizal positioning to explain bi-directional carbon-nutrient transfer in mycorrhizal symbiosis and understand how mycorrhizal fungi mitigate constraints of nutrient uptake efficiency in thicker roots.

Results

Nutrient uptake per unit carbon investment declines with increasing root diameter due to higher carbon demands across thicker cortical tissues in both mycorrhizal and non-mycorrhizal roots. Mycorrhizal fungi achieve constant nutrient benefit per unit carbon investment (k_ncf) regardless of root radius. Positioning arbuscules in inner cortical layers minimizes carbon cost of nutrient transport to the stele, with greater energy savings in thicker roots.

Conclusion

Root anatomical allometry provides structural basis for energy-efficient bi-directional resource exchange between roots and mycorrhizal fungi. This framework reconciles anatomical variation with functional efficiency and offers new understanding of coevolution between roots and mycorrhizal fungi in response to environmental changes including atmospheric CO2 decline.
  • Published in:Nature Communications,
  • Study Type:Theoretical Framework Study,
  • Source: 10.1038/s41467-025-64553-1, PMID: 41027965
Scroll to Top