Effect Of Organic P Sources On Characteristics Of P Assimilation And Accumulation In Polygonum Hydropiper

Excess phosphorus (P) in soils raises water eutrophication process due to its surface runoff or leaching. Plant-assisted approaches are proven to be a promising strategy for extracting excess P from P enriched soil, surface runoff or wastewater. Water-soluble P primarily existed as organic P (Po), and Po in large amounts in water environments. Therefore, Po might be a potential threat to water body. So, how to effectively and quickly remove excess Po from soil and water is particularly important. Experiments were carried out to investigate the effect of Po sources on rhizosphere process, root physiological adaptations, and P accumulation characteristics in a mining ecotype (ME) of P. hydropiper screened as P accumulator earlier, with a non-mining ecotype (NME) as contrast. The relationship between root physiological mechanisms and the ability of P accumulation of P. hydropiper from Po were also elucidated in this study. The following is a summary of the primary results:1) Maximum biomass was noticed in soil amended with 100 g kg-1.Tissue P content increased apparently with increasing manure levels. A 1.14- and 1.11-fold P content in stem and leaf was observed in the ME compared to the NME, respectively. The ME demonstrated higher bioaccumulation coefficient (BCF) and translocation ratio than that of the NME. Shoot P accumulation reached its peak value at 100 g kg-1 and varied from 25.79 to 65.94 mg plant-1 for the ME, from 16.16 to 56.86 mg plant-1 for the NME. A lower value of rhizosphere AP and pH in theME were noticedrelativeto the NME. Substantial conversion of swine manure P was the fractions of H2O-P and NaHCO3-Pi in rhizosphere of both ecotypes after swine manure addition. Rhizosphere H2O-P concentration of both ecotypes depleted, however, HCl-P and residual-P had no significant depletion in the rhizosphere of both ME and NME regardless of swine manure treatments. Increases in rhizosphere NaHCO3-Pi and NaOH-Pi of the ME were observed compared to the corresponding bulk soil except for 200 g kg-1 while the two P fractions decreased in rhizosphere of the NME. Significant depletions of NaHCO3- and NaOH-Po were observed in the rhizosphere of the ME compared to the NME. Soil acid phosphatase and alkaline phosphatase activities increased steadily in response to increasing concentrations of swine manure application. The ME displayed significantly greater rhizosphere acid phosphatase and alkaline phosphatase relative to the NME under 25,50, 100, and 200 g kg-1.2) A significant decrease in shoot biomass was observed in media with 8 mmol L-1 for the ME and 4 mmol L-1 for the NME. The ME showed significantly higher biomass in both shoots and roots compared to the NME at 4,6, and 8 mmol L-1. Shoot P content of the ME and NME increased up to 4 mmol L-1 and root P content reached the maximum of 20.24 g kg-1 for the ME and 9.39 g kg-1 for the NME. The ME displayed higher BCF and lower translocation factor (TF) than the NME. Shoot P accumulation reached the maximum of 11.32 mg plant-1 in the ME and it decreased with the increasing Po levels for the NME. Root P accumulation of the ME significantly increased in response to the increasing Po concentrations, which was 2.06 and 4.78 times higher than that of the NME grown under 6 and 8 mmol L-1, respectively. Root surface area, specific root length and root volume of the ME increased until the Po concentration reached 4 mmol L-1 in the nutrient media. In addition, root length evidently decreased with Po concentration up to 6 mmol L-1 for the ME while a continued decrease in each root morphological parameter was observed in the NME grown in the increasing Po concentrations. Furthermore, the ME showed higher total root length, specific root length, root volume, root surface area compared to the NME, indicating that fine root morphology provided the basic conditions to enhance P uptake of the ME from high Po media.3) Biomass of the ME significantly increased with the growth period prolonged and it was significantly higher that the NME at 7 weeks. Tissue P content of the ME ranged from 5.08 g kg-1 to 10.62 g kg-1 while it varied between 4.26 g kg-1 and 8.74 g kg-1. A highest P accumulation rate in shoot and whole plant was noticed in the ME when grown at 7 weeks, which was 1.23 and 1.39 times higher than that in the NME, suggesting that the ME had the greatest ability of P accumulation at 7 weeks. P mainly distributed in stems of both ecotypes. Shoot P accumulation inthe ME seedlings increased in response to the prolonged growth period and it reached 47.17 and 56.43 mg plant-1 at 7 and 9 weeks, respectively, and it was 139% and 125% higher than the NME. Total root length, surface area, and volume significantly increased with the growth period prolonged and they were notablely higher in the ME compared to the NME. Significant increases in root acid phosphatase (Apase) and phytase activities were observed in both ecotypes with growth period prolonged while a peak value was noticed in root phytase of both ecotypes grown at 7 weeks. Both enzyme activities were higher in the ME than the NME.4) Biomass and P content in stem and leaf of both ecotypes fed with IHP and Pi were significantly greater than those supplied with G1P, AMP and ATP. Shoot P accumulation of both ecotypes was in the order of Pi>IHP>G1P>AMP>ATP. Shoot P accumulation in the ME, ranging from 11.62 mg plant-1 to40.02 mg plant-1, was significantly higher compared to NME seedlings. Maximum total root length, root surface area and root volumewas observed in both ecotypes treated with Pi, followed by IHP. Greater total root length, root surface area and root volumewas observed inthin rootwith diameter ≤0.48 mm of the ME compared to the NME, indicating that development and allocation of fine root might contribute to P assimilation of the ME from Po media. Higher Apase activity in root extracts was observed in the ME grown under IHP and Pi while the minimum phytase activity in root extracts was noticed in ATP compared to the other P sources. The ME showed higher secreted Apase and phytase activities under all Po sources relative to Pi.Higher secreted Apase and phytase activities were detected in the ME treated with different P sources relative to the NME, suggesting that enhanced root productions and secretions of Apase and phytase may be responsible for increased mineralization of various Po to release available P for ME seedlings growth and P uptake.