# Divergent Phosphorus‐Mining Strategies in Simple and Compound Cluster Roots in Extremely Phosphorus‐Impoverished Soils in Southwest Australia

## TL;DR

Plants in southwest Australia use different root strategies to absorb phosphorus from very poor soils, either by growing more roots or by being more efficient with fewer roots.

## Contribution

This study reveals two distinct phosphorus-mining strategies in cluster roots of Proteaceae and Fabaceae species in phosphorus-poor soils.

## Key findings

- Banksia species produce compound cluster roots with greater biomass and higher phosphorus absorption.
- Hakea and Grevillea species use simple cluster roots with higher phosphorus-acquisition efficiency per root weight.
- Both strategies access similar phosphorus compounds, including those not extracted by NaOH-EDTA solutions.

## Abstract

Most Proteaceae and some Fabaceae species produce specialised cluster roots (CRs), and are abundant in severely phosphorus (P)‐impoverished soils in southwest Australia. Two types of CRs, compound and simple, have been identified. However, the difference in their P‐mining strategies remains unclear. Therefore, we conducted glasshouse and field experiments to compare the P‐acquisition strategies among 18 CR‐producing species in Proteaceae and Fabaceae. Proteaceae produced a significantly larger mass of CRs than Fabaceae. Particularly, Banksia species produced the largest mass of compound CRs and exhibited the greatest net plant‐absorbed P in pots and consistently higher mature leaf manganese concentration in the field. In contrast, Hakea and Grevillea species produced less mass of simple CRs but three times as much soil adhered to their CRs per CR dry weight, resulting in greater absorbed P per CR weight. All plants depleted similar P compounds from soil and accessed c. 52% of P that was not extracted by a NaOH‐EDTA solution, suggesting that both CRs shared a common physiological function for mining scarcely available P. This study highlights two divergent P‐acquisition strategies: greater biomass investment in compound CRs versus greater P‐acquisition efficiency in simple CRs.

Divergent phosphorus‐mining strategies that native plants have evolved as adaptations to severely phosphorus‐impoverished soils in southwest Australia: greater biomass investment in compound cluster roots versus greater phosphorus‐acquisition efficiency in simple cluster roots.