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

Abstract

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.

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

“…Acacia rostellifera foliar Mn increased with soil age in all soil treatments, and this trend was particularly strong in the “field soil” as soil P declined. Increase in foliar Mn is consistent with greater reliance on carboxylates for P acquisition in P‐poor soils (Abrahão, Ryan, Laliberté, Oliveira, & Lambers, ; Lambers et al., ; Pang et al., ). Interestingly, this trend remained in the average and specific inoculum soil treatments suggesting that specific fungi may have led to increased carboxylate exudation.…”

Xylomelum occidentale (Proteaceae) accesses relatively mobile soil organic phosphorus without releasing carboxylates

“…There are exceptions in some Mn hyperaccumulators with putative mycorrhizal associations, but their Mn‐uptake mechanisms have not been investigated (Lambers, Hayes, et al, 2015) and at least some of these release carboxylates (Canton et al., 2016). The intermediate leaf [Mn] of Hibbertia hypericoides (Dilleniaceae), which belongs to a family known to comprise species that do not release carboxylates likely results from being in the vicinity of carboxylate‐releasing plants, for example, Banksia species (Abrahão, Ryan, Laliberté, Oliveira, & Lambers, 2018; Muler, Oliveira, Lambers, & Veneklaas, 2014; Yu, Li, et al, 2020; Yu, Zhang, et al, 2020). When searching for roots of Hibbertia hypericoides , we invariably found them associated with cluster roots of neighbouring banksias in this study.…”

Biotic and abiotic plant–soil feedback depends on nitrogen‐acquisition strategy and shifts during long‐term ecosystem development

“…This is because differences in other abiotic and/or biotic factors along the chronosequence not considered in our study might also influence PSF. However, this chronosequence and its soils have been extensively studied (e.g., Abrahão, Ryan, Laliberté, Oliveira, & Lambers, ; Albornoz et al, ; Hayes et al, ; Laliberté et al, , ; Teste, Veneklaas, Dixon, & Lambers, ; Turner & Laliberté, ; Zemunik et al, , ), enabling us to adopt a sampling design that maximises variation in soil age (i.e., soil chemistry; in particular, soil fertility, N and P availability) while minimising variation in other factors (e.g., climate, topography). Therefore, to further advance our understanding of PSF during long‐term ecosystem development, future studies should focus on PSF experiments involving soil nutrient manipulation, or test PSF responses along other long‐term soil chronosequences.…”