Aims Phosphorus (P) limits crop yield and P-fertilisers are frequently applied to agricultural soils. However, supplies of quality rock phosphate are diminishing. Plants have evolved mechanisms to ...improve Pacquisition and understanding these could improve the long-term sustainability of agriculture. Here we examined interactions between root hairs and arbuscular mycorrhizal (AM) colonisation in barley (Hordeum vulgare L.). Methods Barley mutants exhibiting different root hair phenotypes, wild type barley and narrowleaf plantain (Plantago lanceolata L.) were grown in the glasshouse in P-sufficient and P-deflcient treatments and allowed to develop AM colonization from the natural soil community. Plants were harvested after 6 weeks growth and root hair length, AM-fungal colonisation, shoot biomass and P-accumulation measured. Results Under P-deflcient conditions, root hair length and AM colonisation were negatively related suggesting that resources are allocated to root hairs rather than to AM fungi in response to P-deficiency. There was evidence that barley and narrowleaf plantain employed different strategies to increase P-acquisition under identical conditions, but root hairs were more effective. Conclusions This research suggests future barley breeding programmes should focus on maintaining or improving root hair phenotypes and that pursuing enhancements to AM associations under the prevalent agricultural conditions tested here would be ineffectual.
