Legume crops use a phosphorus-mobilising strategy to adapt to low plant-available phosphorus in acidic soil in southwest China

Phosphorus (P) deficiency significantly affects crop productivity, especially legume crops. Therefore, it is important to understand the P-acquisition strategies of different leguminous crops. In this study, we undertook a pot experiment with 11 legume crops (soybean, faba bean, pea, cowpea, common bean, lentil, adzuki bean, chickpea, grass pea, red kidney bean and common vetch) to investigate P-acquisition strategies related to root morphology, organic acid and acid phosphatase exudations, and arbuscular mycorrhizal fungi (AMF) colonisation under low (4.4 mg/kg) and optimal (40 mg/kg) P conditions. The results revealed that P deficiency significantly decreased bio-mass and P accumulation, root length (10.5%), and root surface area (7.9%), increased organic acid exudation (80.2%) and acid phosphatase activity (16.8%), and did not affect root diameter or root AMF colonisation rate. Principal component analysis revealed a positive correlation between organic acid exudation and acid phosphatase activity, while root length and root surface area negatively correlated with organic acid exudation, acid phosphatase activity and root AMF colonisation rate. P accumulation positively correlated with root length, surface area, and diameter but negatively correlated with organic acid exudation, acid phosphatase activity, and AMF colonisation rate. These findings confirmed the following: (1) legume crops use a P-mobilisation strategy related to organic acid exudation and acid phosphatase activity to acquire P under low soil P conditions; (2) organic acid exudation coincided with acid phosphatase activity to mobilise soil inorganic and organic P, improving P accumulation; (3) a trade-off exists between the P-scavenging strategy related to root morphology traits and mobilisation strategy.