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

1. The vast majority of terrestrial plants form root symbioses with
arbuscular mycorrhizal (AM) fungi to enhance nutrient (particularly
phosphorus, P) acquisition, but some plant species also form dual
symbioses involving ectomycorrhizal (ECM) fungi, with a subset of those
also forming triple symbioses also involving dinitrogen (N2)-fixing
bacteria. Whether these plants show plasticity in root symbioses to
optimise nutrient acquisition depending on the type and strength of soil
nutrient limitation (e.g., N vs. P) has been suggested, yet empirical
evidence remains limited. Alternatively, the degree of investment or
‘preference’ in particular root symbioses might simply reflect differences
in inoculum potential among soils of contrasting nutrient availability,
reflecting adaptations of root symbionts to different edaphic 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 increasing age and contrasting nutrient availability
from an Australian long-term soil chronosequence to disentangle the
relative importance of abiotic factors (e.g., soil nutrient availability
and stoichiometry) and biotic factors (e.g., soil inoculum potential) in
determining root colonisation patterns and functional outcomes of these
multiple root symbioses. 3. For both plant species, we found clear
hump-shaped plant growth patterns along the pedogenesis-driven gradient in
soil nutrient availability, with peak growth in intermediate-aged soils,
while high levels of mycorrhizal colonisation by the ‘preferred’ root
symbionts was maintained. We found large increases (540%) in foliar
manganese concentrations with increasing soil age and declining P
availability, suggesting that plants are also relying on the release of
carboxylates to help acquire P in the most impoverished soils. Finally, we
found that soil abiotic properties, such as strong differences in soil
nutrient availabilities, are generally more important than soil inoculum
potential in explaining these shifts in our plant and root responses. 4.
Synthesis. Our study suggests that plants capable of forming multiple root
symbioses show plasticity in their nutrient-acquisition strategies
following shifts in soil nutrients during long-term ecosystem development,
yet maintain a preference for certain root symbionts despite changes in
soil microbial inoculum.