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Phosphorus‐ and nitrogen‐acquisition strategies in two Bossiaea species (Fabaceae) along retrogressive soil chronosequences in south‐western Australia

Abrahão, Anna, Ryan, Megan H., Laliberté, Etienne, Oliveira, Rafael S., Lambers, Hans
Physiologia plantarum 2018 v.163 no.3 pp. 323-343
Bossiaea, carboxylic acids, chronosequences, coasts, ecosystems, exudation, greenhouses, intraspecific variation, leaves, legumes, manganese, mycorrhizae, nitrogen, nitrogen fixation, nodulation, nutrient availability, nutrient uptake, phosphorus, plant exudates, plant nutrition, soil, soil formation, soil nutrients, Western Australia
During long‐term ecosystem development and its associated decline in soil phosphorus (P) availability, the abundance of mycorrhizal plant species declines at the expense of non‐mycorrhizal species with root specialisations for P‐acquisition, such as massive exudation of carboxylates. Leaf manganese (Mn) concentration has been suggested as a proxy for such a strategy, Mn concentration being higher in non‐mycorrhizal plants that release carboxylates than in mycorrhizal plants. Shifts in nitrogen (N)‐acquisition strategies also occur; nodulation in legumes is expected at low N availability, when sufficient P is available. We investigated whether two congeneric legume species (Bossiaea linophylla and Bossiaea eriocarpa) occurring along two long‐term chronosequences on the south‐western Australian coast and grown in a glasshouse at varying N and P supply exhibited plasticity in nutrient‐acquisition strategies. We hypothesised that the shifts in nutrient limitation and nutrient‐acquisition strategies at the community level would also be found at the species level. Leaf N: P ratios and the responses to nutrient availability suggested that growth of both species exhibited P‐limitation in all treatments, due to the very high leaf [N] of legumes afforded by symbiotic N‐fixation. Mycorrhizal colonisation was not greater at higher P supply, and root exudation of carboxylates was not stimulated at low P supply; both were unrelated to leaf [Mn]. However, nodule production declined with increasing N supply. We conclude that intraspecific variation in nutrient‐acquisition and use is low in these species, and that the variation at the community level, observed in previous studies, is likely driven by high‐species turnover.