Multimodal correlative imaging and modelling of phosphorus uptake from soil by hyphae of mycorrhizal fungi

Summary

Phosphorus (P) is essential for plant growth. Arbuscular mycorrhizal fungi (AMF) aid its uptake by acquiring P from sources distant from roots in return for carbon. Little is known about how AMF colonise soil pore￢ﾀﾐspace, and models of AMF￢ﾀﾐenhanced P￢ﾀﾐuptake are poorly validated.

We used synchrotron X￢ﾀﾐray computed tomography to visualize mycorrhizas in soil and synchrotron X￢ﾀﾐray fluorescence/X￢ﾀﾐray absorption near edge structure (XRF/XANES) elemental mapping for P, sulphur (S) and aluminium (Al) in combination with modelling.

We found that AMF inoculation had a suppressive effect on colonisation by other soil fungi and identified differences in structure and growth rate between hyphae of AMF and nonmycorrhizal fungi. Our results showed that AMF co￢ﾀﾐlocate with areas of high P and low Al, and preferentially associate with organic￢ﾀﾐtype P species over Al￢ﾀﾐrich inorganic P.

We discovered that AMF avoid Al￢ﾀﾐrich areas as a source of P. Sulphur￢ﾀﾐrich regions were found to be correlated with higher hyphal density and an increased organic￢ﾀﾐassociated P￢ﾀﾐpool, whilst oxidized S￢ﾀﾐspecies were found close to AMF hyphae. Increased S oxidation close to AMF suggested the observed changes were microbiome￢ﾀﾐrelated. Our experimentally￢ﾀﾐvalidated model led to an estimate of P￢ﾀﾐuptake by AMF hyphae that is an order of magnitude lower than rates previously estimated ￢ﾀﾓ a result with significant implications for the modelling of plant￢ﾀﾓsoil￢ﾀﾓAMF interactions.