Data from: Stoichiometric N:P flexibility and mycorrhizal symbiosis favor plant resistance against drought

1. Drought induces changes in the nitrogen (N) and phosphorus (P) cycle
but most plant species have limited flexibility to take up nutrients under
such variable or unbalanced N and P availability. Both the degree of
flexibility in plant N:P ratio and of root symbiosis with arbuscular
mycorrhizal (AM) fungi might control plant resistance to drought-induced
changes in nutrient availability, but this has not been directly tested.
2. Here, we examined the role of plant N:P stoichiometric status and
mycorrhizal symbiosis in the drought-resistance of dominant and
subordinate species in a semi-natural grassland. 3. We reduced water
availability using rainout shelters (control vs drought) and measured how
plant biomass responded for the dominant and subordinate species. We then
selected a dominant (Paspalum dilatatum) and a subordinate species
(Cynodon dactylon), for which we investigated the N:P stoichiometric
status, mycorrhizal root colonization and water-use efficiency. 4. The
biomass of all dominant plant species, but not subordinate species,
decreased under drought. Drought increased soil available nitrogen, and
thus increased soil N:P ratio, due to decreasing plant N uptake. The
dominant Paspalum dilatatum showed a high degree of plant N:P homeostasis
and a considerable reduction in biomass under drought. At the opposite,
the more flexible subordinate species Cynodon dactylon increased its N
uptake and water-use efficiency, apparently due to stronger symbiosis with
mycorrhizae, and maintained its biomass. 5. Synthesis. We conclude that
the maintenance of N:P homeostasis in dominant species, possibly because
of a large root nutrient foraging capacity, becomes inefficient when water
stress limits N mobility in the soil. By contrast, we demonstrate that
higher stoichiometric N:P flexibility coupled with stronger mutualistic
association with mycorrhizae allow subordinate species to better withstand
drought perturbations. Using a stoichiometric approach in a field
experiment, our study provides for the first time clear and novel
understandings of the mechanisms involved in drought-resistance within the
plant-mycorrhizae-soil system.