Arbuscular Mycorrhizal Fungi Alter the Community Structure of Ammonia Oxidizers at High Fertility via Competition for Soil NH4+
Nitrification represents a central process in the cycling of nitrogen (N) which in high-fertility habitats can occasionally be undesirable. Here, we explore how arbuscular mycorrhiza (AM) impacts nitrification when N availability is not limiting to plant growth. We wanted to test which of the mechanisms that have been proposed in the literature best describes how AM influences nitrification. We manipulated the growth settings of Plantago lanceolata so that we could control the mycorrhizal state of our plants. AM induced no changes in the potential nitrification rates or the estimates of ammonium oxidizing (AO) bacteria. However, we could observe a moderate shift in the community of ammonia-oxidizers, which matched the shift we saw when comparing hyphosphere to rhizosphere soil samples and mirrored well changes in the availability of ammonium in soil. We interpret our results as support that it is competition for N that drives the interaction between AM and AO. Our experiment sheds light on an understudied interaction which is pertinent to typical management practices in agricultural systems.
KeywordsAmmonium oxidizers Arbuscular mycorrhiza Glomeromycota Mycorrhizal hyphosphere Nitrification potential
We thank James Prosser for giving us the cultures of the ammonia oxidizers which we used as positive controls and for providing invaluable comments on an earlier version of the manuscript, Jens Rolff for granting access to laboratory equipment and consumables and Stefan Hempel for technical support. The project was funded by the EU-framework FP7-People project: AMNitrification: “A mechanistic analysis of the impact of arbuscular mycorrhiza on ammonia oxidizing community dynamics and nitrification potential rates in N-limited soils” awarded to SDV (Grant agreement number 300298).
Conceived the study, run and harvested the experiment and assayed biochemical parameters: SDV; shared the molecular work: SDV, EV and OM; extracted hyphae from soil: IM; did the statistical analysis and bioinformatics: SDV; SDV wrote the manuscript with the help of EV, RS and MCR and everybody provided comments.
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