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Root anatomy governs bi-directional resource transfer in mycorrhizal symbiosis

Summary

This research reveals how the shape and structure of plant roots influence their ability to exchange nutrients and carbon with symbiotic fungi. The study shows that thicker roots face challenges in efficiently acquiring nutrients because they require more energy to transport nutrients across their thicker outer tissues. Fortunately, mycorrhizal fungi can help overcome this limitation when they position themselves deeper within the root structure, reducing the energy cost of moving nutrients to the plant’s vascular system.

Background

Plants form mycorrhizal symbioses to enhance nutrient acquisition, yet 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 diversity and function.

Objective

To develop a theory of bi-directional carbon-nutrient transfer that integrates root anatomy, energetic costs, and mycorrhizal positioning. The study aims to reconcile anatomical variation, symbiotic structure, and functional efficiency across root types and mycorrhizal strategies.

Results

Nutrient uptake per unit carbon or energy investment declines with increasing root diameter due to higher carbon demands across thicker cortical tissues. Mycorrhizal fungi mitigate this constraint by enabling more carbon-efficient nutrient uptake, particularly when arbuscules are positioned in inner cortical layers, minimizing the carbon cost of transporting nutrients to the stele.

Conclusion

Root anatomical allometry provides a structural basis for energy-efficient bi-directional resource exchange between roots and mycorrhizal fungi. The spatial optimization of arbuscule positioning in inner cortical layers reduces energy costs and offers new insights into the coevolution between roots and mycorrhizal fungi under environmental changes.
  • Published in:Nature Communications,
  • Study Type:Theoretical Study with Mathematical Modeling,
  • Source: 10.1038/s41467-025-64553-1, PMID: 41027965
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