Organic nitrogen utilisation by an arbuscular mycorrhizal fungus is mediated by specific soil bacteria and a protist

Abstract

Arbuscular mycorrhizal (AM) fungi lack efficient exoenzymes to access organic nutrients directly. Nevertheless, the fungi often obtain and further channel to their host plants a significant share of nitrogen (N) and/or phosphorus from such resources, presumably via cooperation with other soil microorganisms. Because it is challenging to disentangle individual microbial players and processes in complex soil, we took a synthetic approach here to study 15N-labelled chitin (an organic N source) recycling via microbial loop in AM fungal hyphosphere. To this end, we employed a compartmented in vitro cultivation system and monoxenic culture of Rhizophagus irregularis associated with Cichorium intybus roots, various soil bacteria, and the protist Polysphondylium pallidum. We showed that upon presence of Paenibacillus sp. in its hyphosphere, the AM fungus (and associated plant roots) obtained several-fold larger quantities of N from the chitin than it did with any other bacteria, whether chitinolytic or not. Moreover, we demonstrated that adding P. pallidum to the hyphosphere with Paenibacillus sp. further increased by at least 65% the gain of N from the chitin by the AM fungus compared to the hyphosphere without protists. We thus directly demonstrate microbial interplay possibly involved in efficient organic N utilisation by AM fungal hyphae.

Arbuscular Mycorrhiza and Nitrification: Disentangling Processes and Players by Using Synthetic Nitrification Inhibitors

“…Interestingly, SNI application did not show a significant effect on the acquisition of 15 N by mycorrhizal plants from the organic amendment. This indirectly supports the previous hypothesis that AM fungal hyphae effectively take up ammonium ions from the soil solution shortly after organic N mineralization, preventing this N from entering the nitrification pathway ( 16 , 40 , 41 ). Alternatively, it is possible that AM fungal hyphae themselves produced and excreted metabolites that inhibited the activity of ammonium oxidizing microorganisms by acting as biological nitrification inhibitors (BNI).…”

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

“…Therefore, similar to the area affected by roots (i.e. the rhizosphere), a ‘hyphosphere’ of AMF can be a zone of increased bacterial abundance, and a site of localised biochemical activity (Rozmos et al ., 2021 ).…”

Ensuring future food security and resource sustainability: insights into the rhizosphere

“…The gain of N by the AMF from the organic N source increased by at least 65% with the addition of Paenibacillus sp. and a protist Polysphondylium pallidum to the hyphosphere (Rozmo s et al, 2022). Plants integrate AMF and their extraradical hyphae and hyphosphere microbiome to exploit nutrient resources in soil efficiently, greatly expanding the foraging capacity of roots.…”