Objectives Appropriate nitrogen (N) application can improve phosphorus (P) accumulation in plants. The effect were testified using phosphorous hyper accumulator plants in this paper, which would provide practical support for effective remediation in environmental P pollution and the non-point source pollution of P.
Methods Taking mining ecotype (ME) of Polygonum hydropiper as tested materials and non-mining ecotype (NME) as control, a pot experiment was conducted in a greenhouse under natural light at Sichuan Agricultural University, Sichuan Province, China in 2015. The used soil, calcareous alluvial soil, was applied 800 mg/kg of P and then designed N levels (0, 25, 50, 100 and 200 mg/kg soil) after standing for 4 weeks for stabilizing. The soil available P concentration became 425 mg/kg afterwards. Total 6 kg of the treated soils, 2.5 kg was loaded inside the root bags with 38 µm of pores in the central of pots and 3.5 kg outside the bags. 2 plants at age of three leaves and one sprout were transplanted inside the root bags for each pot, and the soil moisture was kept 75% of the field capacity. After growing for 10 weeks, the plants were harvested, the biomass were weighed and the P concentrations were determined. The soil samples both inside and outside the root bags were raped off the top 2 cm surface, and the available P concentrations were analyzed separately.
Results 1) The biomass, P concentration and P accumulation in shoots of ME reached the maximum under the N application rate of 100 mg/kg, which were 4.57, 1.33 and 6.10 times of those in the control plants. The P accumulation in shoots was increased to 228 mg/plant. The P concentration and P accumulation in shoots of ME were significantly higher than those in NME under N application rate of 50, 100 and 200 mg/kg, respectively, which were 1.14, 1.08, 1.03 and 1.25, 1.11, 1.09 times of NME. 2) The biomass, P concentration and P accumulation in roots of ME were increased with increasing N application. ME presented lower P concentration and P accumulation in roots, the P accumulation in roots were only 39.5% - 84.2% of NME. 3) Under the condition of N application, both bioaccumulation coefficient and translocation factor of P in ME were larger than 1, and reached the maximum under 100 mg/kg N application, which were 12.5 and 1.33, respectively. The bioaccumulation coefficient and translocation factor of P in ME were significantly higher than those in NME, which were 1.08 and 1.53 times of NME under 100 mg/kg N application, respectively. This indicated that the higher P transportation from roots to shoots in ME than the NME. 4) The N application improved P availability in rhizosphere soils of ME, which was more pronounced at 50, 100 and 200 mg/kg. In addition, it was higher than the corresponding bulk soil at any N treatments, thus promoting its P accumulation.
Conclusions N application could effectively improve the up transportation and accumulation of P in the shoot of mining ecotype of Polygonum hydropiper, which are obtained by increasing the shoot biomass and the availability of soil P under high P condition. The optimal N application was 100 mg/kg in the pot experimental condition, and further experiment is needed for the practice of the remediation of P pollution in large scale.
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