Maize, wheat, and soybean root traits depend upon soil phosphorus fertility and mycorrhizal status

Strong effects of plant identity, soil nutrient availability or mycorrhizal fungi on root traits have been well documented, but their interactive influences on root traits are still poorly understood. Here, three crop species (maize, wheat and soybean) were grown under four phosphorus (P) addition levels (0, 20, 40 and 60 mg P kg^-1 dry soil), and plants were inoculated with or without five combined arbuscular mycorrhizal fungal (AMF) species. Plant biomass, nutrient contents, root traits (including total root length, average root diameter, specific root length and root tissue density) and plants' mycorrhizal responses were measured. Crop species, P level, AMF, and their interactions strongly affected plant biomass and root traits. P fertilization promoted plant growth but reduced mycorrhizal benefits on plant biomass and nutrient uptake. Root traits of maize were sensitive to P addition only under the non-mycorrhizal condition, whilst most root traits of soybean and wheat plants were responsive to mycorrhizal inoculation but not P addition. Mycorrhizal colonization reduced the root plasticity in response to P fertility for maize but not for wheat or soybean. This study highlights the importance of soil nutrient fertility and mycorrhizal symbiosis in influencing root traits.