Nitrogen application enhanced phosphorus-phytoextraction of Polygonum hydropiper from high phosphorus soil in relation to rhizosphere phosphorus fractions

Abstract

Nitrogen (N) application provides an effective way to enhance the efficiency of phosphorus (P) -phytoextraction. However, it remains unknown how N application facilitates P accumulation of P-accumulating plant by regulating rhizosphere P fractions. We investigated the P accumulation, rhizosphere P fractions and phosphatase activities of Polygonum hydropiper (P. hydropiper), a P-accumulating herb, across four growth periods in high-P soil (800 mg P kg⁻¹) with different N applications (0 and 100 mg N kg⁻¹). N application increased shoot P accumulation of P. hydropiper compared with the control, with the greatest shoot P accumulation in mining ecotype (ME) of P. hydropiper at 12 weeks. Compared with bulk soil, the concentration of H₂O-Pi (Pi, inorganic P) and NaHCO₃-P increased but the concentration of H₂O-Po (Po, organic P) and NaOH-Po decreased in the rhizosphere after N application. Compared with the control, the stronger positive effects of NaHCO₃-Po and HCl-Po on H₂O-Pi and NaOH-Pi were observed after N application. The high activities of acid phosphomonoesterase (ACP) and alkaline phosphomonoesterase (ALP) in the rhizosphere of two ecotypes led to mineralization of Po. Overall, these results suggested that N application can enhance P-phytoextraction capability of P. hydropiper from high-P soil by increasing phosphatase activities and transforming P fractions. Our results also provided a practical optimization to extract excess P from high-P soil by P-accumulating plant.