Soil Legacy Phosphorus Transformation in Long-term Fertilized Phaeozems Soil under Maize/Soybean Intercropping

Abstract

Root exudate could improve crop productivity and phosphorus (P) acquisition in maize/soybean intercrops. However, the synergistic effects between intercropped plants, the regulation of soil phosphatase activity, and P transformation corresponding to it remain elusive. Three kinds of root separation treatments, solid barrier (SB), mesh barrier (MB), and no barrier (NB), using pot experiment, were conducted to quantify the effects of plants, rhizosphere exudates exchange and the complete root interaction. Sequential extraction and 31P-NMR spectroscopic analysis methods complement each other, which can better explain the combination forms of P elements. This work suggests that maize under NB stimulated a decrease in NH4F-inorganic P (Pi, 7.91%) and occluded Pi (7.46%) compared to those under SB. In the presence of maize signaling chemicals (MB treatment), the percentage of mononucleotides was enriched, while neo-inositol hexakisphosphate, β-glycerophosphate, and phosphocholine declined in the soybean rhizosphere compared to SB. Under both two plants, phosphodiesterase (PDE) activity was negatively correlated with pyrophosphate. The activity of alkaline phosphatase (ALP) was the highest in the MB treatment of maize and soybean, which increased from 33.80 to 44.5 and 41.92 (ug g− 1 h− 1) compared with bulk soil. Maize under monocropping mainly mobilizes acid phosphatase (ACP), but it is converted to ALP and PDE when intercropping with soybean. Knowledge of P species in P-rich soils helps assess P potential transfer and provides new evidence for the value of cereal-legume intercrops in reducing fertilizer input.