EXPLAINING COEXISTENCE OF NITROGEN FIXING AND NON-FIXING RHIZOBIA IN LEGUME-RHIZOBIA MUTUALISM USING MATHEMATICAL MODELING

GABRIEL MOYANO; DIANA E. MARCO; DAMIAN KNOPOFF; GERMAN TORRES; CRISTINA TURNER

MATHEMATICAL BIOSCIENCES

ELSEVIER SCIENCE INC

Lugar: Amsterdam; Año: 2017

0025-5564

In the mutualism established between legumes and soil bacteria known asrhizobia, bacteria from soil infect plants roots and reproduce inside root nod-ules where they x atmospheric N2 for plant nutrition, receiving carbohydratesin exchange. Host-plant sanctions against non N2 xing, cheating bacterialsymbionts have been proposed to act in the legume-Rhizobium symbiosis, topreserve the mutualistic relationship. Sanctions include decreased rhizobial survival in nodules occupied by cheating rhizobia. Previously, a simple population model experimentally based showed that the coexistence of xing and cheating rhizobia strains commonly found in eld conditions is possible, and that the inclusion of sanctions leads to the extinction of cheating strains in soil. Here, we extend the previous model to include other factors that could complicate the sanction scenario, like horizontal transmission of symbiotic plasmids, turning non-nodulating strains into nodulating rhizobia, and competition between fixing and cheating strains for nodulation. In agreement with previous results, we show that plant populations persist even in the presence of cheating rhizobia without incorporating any sanction against the cheater populations in the model, under the realistic assumption that plants can at least get some amount of fixed N2 from the eectively mutualistic rhizobia occupying some nodules. Inclusion of plant sanctions leads to the unrealistic extinction of cheater strains in soil. Our results agree with increasing experimental evidence and theoretical work showing that mutualisms can persist in presence of cheating partners.