Root morphology and phosphorus requirements of twelve tropical pasture species grown in a controlled environment

Jonathan McLachlan; Richard Flavel; Christopher Guppy

Just Accepted

This article has been peer reviewed and accepted for publication. It is in production and has not been edited, so may differ from the final published form.

Root morphology and phosphorus requirements of twelve tropical pasture species grown in a controlled environment

Jonathan McLachlan , Richard Flavel, Christopher Guppy

Abstract

Context Tropical pasture species are often established in phosphorus (P)-deficient soils that can limit plant productivity and persistence. Little is known about the root traits and critical P requirements of many tropical grasses and legumes. Characterisation of these traits would allow P-efficient species to be used when soil fertility is poor and agricultural inputs are limited, or for important root traits to be considered if selecting for P efficiency. Aims To assess the shoot yield, root morphology, P acquisition and critical P requirements of a range of commonly grown tropical pasture species. Methods Five tropical grasses and seven tropical legumes were grown in pots containing a light-textured, low-P soil to investigate shoot growth and root traits in response to applied P (0–120 mg P kg–1 soil). Key Results The shoot yield of each species increased in response to applied P, yet there were differences in maximum shoot yield (1.7–9.8 g DM pot–1) and critical external P requirements (12.8–38.0 mg P kg–1 soil) among the species. The acquisition of P was associated to varying degrees with the development of root length when plants were grown in soil that enabled near-maximum growth (e.g. R2 = 0.71–0.77 for the grasses and R2 = 0.14–0.43 for the legumes in the 15–30 mg P kg–1 soil treatments). Conclusions Longer roots were associated with higher shoot yields and better P-acquisition efficiency, and the grasses generally had comparable or lower critical P requirements than the legumes. Implications Phosphorus-efficient species should be used when soils are known to be P deficient, or where P fertilisation is not an option, and grasses and legumes could be paired based on their P requirements.

CP25049 Accepted 21 August 2025