Subcellular distribution and chemical form of phosphorus involved in alleviating phosphorus toxicity of the phosphorus-accumulator Polygonum hydropiper.

Polygonum hydropiper is a dominant plant species in Shifang phosphorus (P) mine area and is a promising P-accumulator used for P-phytoextraction. To date, little information is available on the physiological response involved in alleviating P toxicity of P. hydropiper under high P. A pot experiment was carried out to investigate growth, P subcellular distribution, chemical forms in two ecotypes of P. hydropiper under high levels (1, 4, and 8 mmol P L-1 ) of inorganic P (Pi) and organic P (Po), supplied as KH2 PO4 and myo-inositol hexaphosphoric acid dodecasodium salt, respectively. The mining ecotype (ME) showed a greater ability to tolerate high P than the non-mining ecotype (NME), as shown by its superior growth with undamaged leaf anatomical structure. The ME showed 1.3-2.2 times greater shoot P accumulation than the NME. More than 93% of P accumulated in tissue cell wall and soluble fraction. The increasing P treatments increased all tissue P forms, especially Pi form. The ME showed significantly higher ester P, nucleic P and insoluble P in tissues than the NME at 8 mmol L-1 ; however, it demonstrated lower Pi, expect for roots at 5 weeks. The percentages of Pi and nucleic P in roots of the ME were higher than other P forms, and the percentages of nucleic P dominated in the leaves. Probably, the combination of preferential distribution of P in cell wall and soluble fraction in tissues and storage of P in low activity as nucleic P in leaves allows the ME to adapt high P.