Plasticity in root symbioses following shifts in soil nutrient availability during long-term ecosystem development

TESTE, FRANÇOIS P.; LALIBERTÉ, ETIENNE

JOURNAL OF ECOLOGY (PRINT)

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2019 vol. 107 p. 633 - 649

0022-0477

1. The vast majority of terrestrial plants form root symbioses with arbuscular mycorrhizal(AM) fungi to enhance nutrient (particularly phosphorus, P) acquisition.However, some plant species also form dual symbioses involving ectomycorrhizal(ECM) fungi, with a subset of those also forming triple symbioses also involvingdinitrogen (N2)‐fixing bacteria. It has been suggested that these plants show plasticityin root symbioses to optimise nutrient acquisition depending on the typeand strength of soil nutrient limitation (e.g., N vs. P), yet empirical evidence remainslimited. Alternatively, the degree of investment or ?preference? in particularroot symbioses might simply reflect differences in inoculum potential among soilsof contrasting nutrient availability, reflecting adaptations of root symbionts to differentedaphic conditions.2. Here, we grew two co‐occurring plant species forming triple (AM/ECM/N2‐fixing;Acacia rostellifera) or dual (AM/ECM; Melaleuca systena) symbioses in soils of increasingage and contrasting nutrient availability from an Australian long‐term soilchronosequence to disentangle the relative importance of abiotic factors (e.g., soilnutrient availability and stoichiometry) and biotic factors (e.g., soil inoculum potential)in determining root colonisation patterns and functional outcomes ofthese multiple root symbioses.3. For both plant species, we found clear hump‐shaped plant growth patterns alongthe pedogenesis‐driven gradient in soil nutrient availability, with peak growth inintermediate‐aged soils, while high levels of mycorrhizal colonisation by the ?preferred?root symbionts were maintained across all soils. We found large increases(540%) in foliar manganese concentrations with increasing soil age and declining Pavailability, suggesting that plants may be relying on the release of carboxylates tohelp acquire P in the most P‐impoverished soils. Finally, we found that soil abioticproperties, such as strong differences in soil nutrient availability, are generallymore important than soil inoculum potential in explaining these shifts in our plantand root responses.4. Synthesis. Our study suggests that plants capable of forming multiple root symbiosesshow plasticity in their nutrient‐acquisition strategies following shifts in soilnutrients during long‐term ecosystem development, yet maintain a preference forcertain root symbionts despite changes in soil microbial inoculum.