Root positioning and trait shifts in Hibbertia racemosa as dependent on its neighbour's nutrient-acquisition strategy.

Nutrient-poor ecosystems globally exhibit high plant diversity. One mechanism enabling species coexistence in such ecosystems is facilitation among plants with contrasting nutrient-acquisition strategies. The ecophysiological processes underlying these interactions remain poorly understood. We hypothesised that root positioning plays a role between sympatric species in nutrient-poor vegetation. We investigated how growth traits of the focal mycorrhizal non-cluster rooted Hibbertia racemosa change when grown in proximity of non-mycorrhizal Banksia attenuata, which produces cluster roots that increase nutrient availability, compared with growth with conspecifics. Focal plants were placed in the centre of rhizoboxes, and we assessed biomass allocation, root system architecture, specific root length and leaf nutrient concentration. When grown with B. attenuata, focal plants decreased root investment, increased root growth towards B. attenuata, and positioned their roots near B. attenuata cluster roots. Specific root length was greater, and the degree of localised root investment correlated positively with B. attenuata cluster-root biomass. Total nutrient contents in the focal individuals were greater when grown with B. attenuata. Focal plants directed their root growth towards the putatively facilitating neighbour's cluster roots, modifying root traits and investment. Preferential root positioning and root morphological traits play important roles in positive plant-plant interactions. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.