Effects of suitable nitrogen application on soil phosphorus fractions and phosphatase activities in rhizosphere microdomain of Pilea sinofasciata

Objectives Suitable nitrogen (N) application can improve the remediation efficiency of phosphorus (P) accumulating plants in soil with excess P. Clarifying the changes of P fractions in the rhizosphere microdomain of P-accumulating plants under suitable N application is beneficial for extracting excess P from soil.

Methods A multi-compartment root box experiment was carried out. And mining ecotype (ME) of Pilea sinofasciata was used as the tested materials, with the non-mining ecotype (NME) being the control. P treatment concentration was 800 mg/kg and N treatment concentration was 0 (CK) and 140 mg/kg. The differences of P accumulation, soil P fractions and phosphatase activities were compared between the two ecotypes of Pilea sinofasciata.

Results 1) The biomass and P accumulation of the two ecotypes significantly increased under suitable N application condition, the shoot biomass and P accumulation of the ME were 1.28 times and 1.45 times than that of the NME, respectively. 2) With suitable N application, the concentration of H₂O-P and NaHCO₃-Pi increased in rhizosphere soil of the two ecotypes. The concentration of H₂O-P and NaHCO₃-Pi were significantly higher in the range of 4 mm away from rhizosphere in the ME, and significantly higher in the range of 4 mm and 2 mm away from rhizosphere in the NME than those in the bulk soil. The concentration of NaHCO₃-Po and NaOH-Pi, NaOH-Po in soil were significantly lower than those in the bulk soil in 6 mm away from the rhizosphere of the two ecotypes. There was no significant difference of soil HCl-Pi, HCl-Po and residual-P between rhizosphere microdomain and bulk soil. The concentration of NaHCO₃-Pi in rhizosphere microdomain of ME was significantly lower than that of NME under the treatment of no N application and suitable N application, and the utilization ability of soil NaHCO₃-Pi of the ME was stronger. 3) Under suitable N application treatment, the activities of phosphatase in rhizosphere soil of two ecotypes of Pilea sinofasciata were higher than that without N application. The activities of soil acid phosphatase and alkaline phosphatase were significantly higher in the microdomain 4 mm and 2 mm away from the rhizosphere than those in the bulk soil, and the phytase activity in the microdomain 8 mm away from the rhizosphere was significantly higher than that in the bulk soil. The soil phosphatase activity in the rhizosphere microdomain of the ME were higher under the treatments of no N application and suitable N application.

Conclusions Under high P condition, suitable N application increased the activities of soil phosphatase in the rhizosphere microdomain of both two ecotypes of Pilea sinofasciata, and the activities of soil phosphatase in the rhizosphere microdomain of the ME were higher, which was conducive to the transformation of soil P in the rhizosphere microdomain from low-availability fractions to high-availability fractions, and promoted plant growth and P accumulation.