Biochar and Arbuscular Mycorrhizal Fungi Play Different Roles in Enabling Maize to Uptake Phosphorus

The addition of biochar alters soil habitats and has an active effect on the symbiotic relationship between plants and mycorrhizal fungi. However, it is still unclear whether this effect alters the strategy of phosphorus uptake by plants. Therefore, pot experiments were conducted in order to investigate the effects of mycorrhizal colonization and biochar addition on plant growth, phosphorus absorption, and rhizosphere Olsen-P supply in maize under two moisture conditions—60% field water capacity (FWC) and 40% FWC. It was found that the addition of biochar increased the colonization rate of arbuscular mycorrhizal fungi (AMF), and all the addition treatments significantly improved maize biomass, peroxidase (POD) activity, chlorophyll content, photosynthetic rate (Pn), plant height, leaf area, shoot phosphorus content, and phosphorus uptake by maize under the two moisture conditions. In addition, biochar had significant effects on root morphology under both water conditions, whereas AMF only showed significant effects under water stress. In contrast, phosphatase activity and microbial activity were higher in the AMF inoculation treatment than in the biochar addition treatment, and the trend was more significant under water stress. Principal component analysis (PCA) showed that root morphology, rhizosphere microbial activity, phosphatase activity, available phosphorus content, and shoot phosphorus content had significant positive correlations. It was concluded that biochar aids plant uptake of phosphorus mainly by regulating root morphology and plant phosphorus content, whereas the large mycelium of AMF enhances microbial activity and phosphatase activity, thereby enabling more efficient phosphorus uptake by maize, especially under conditions of water stress.