| Phosphorus runoff into surface water from a variety of diffuse sources may lead eutrophication. The wetlands which buffer the interactions between uplands and adjacent aquatic systems become a key in phosphorus removal and retention. Phosphorus uptake by aquatic plants may make a significant contribution to the reduction of dissolved phosphorus in moving water toward aquatic systems. Therefore, it is critical to understand how different plants in wetlands take up and retain phosphorus before developing any effective mitigation scheme using plants.A mini-rhizotron experiment was conducted to measure the spatial and temporal dynamics of phosphorus in the rhizosphere solution for four aquatic plants (Alternanthera philoxeroides, Typha latifolia, Sagittaria sagittifolia, Phragmites communis). Meanwhile, In Nansihu wetland (China), micro-suction cups were used to collect samples of soil solution from the rhizosphere of six aquatic plants root (Phragmites communis, Arundo donax, Typha latifolia, Scirpus validus, Zizania aquatica and Alternanthera philoxeroides), and capillary electrophoresis was used to determine the phosphate concentration of the soil solution. Root morphology, phosphorus uptake efficiency, phosphorus use efficiency and organic acids were analyzed to reveal the rhizosphere mechanism of purifying efficiencies for various plants, and to select the plant species of higher purifying efficiency for phosphorus.An obvious variation in P concentration of the soil in the rhizophere was observed. In the mini-rhizotron experiment, A. philoxeroides was the most effective aquatic plant in reducing the water-soluble P of the soil in the rhizosphere (80.5%), the second T. latifolia (41.7%), while S. sagittifolia and P. communis(less than 20%) were the least effective plants. A decreasing phosphorus concentration gradient in soil solution toward the root was observed for both A. philoxeroides and T. latifolia. The phosphorus concentration in the rhizosphere soil solution of A. philoxeroides (2.53 mg·L-1) was lower than that of T. latifolia (5.43 mg·L-1) in the forth sampling day. The field invstigation result indicated that T. latifolia was the most effective in phosphorus retention, followed by P. communis, A. donax and S. validus. Phosphorus in the rhizosphere solution (PO43-, 0.37μg·L-1) was significant lower than the bulk soil solution (PO43-, 0.47μg·L-1) for T. latifolia, but reversed for P. communis, A. donax, S. validus and A. philoxeroides; no significant difference was observed for Z. aquatica. Available phosphorus (Olsen-P) of the rhizosphere soil was fifty percent higher than the non-rhizosphere for A. philoxeroides, and seven to thirty seven percent lower than the non-rhizosphere soil for the other five aquatic plants.A. philoxeroides and T. latifolia were the most effective plants in phosphorus acquisition, but the mechanism was different. A. philoxeroides's more effective phosphorus acquisition was achieved by higher phosphorus uptake efficiency, with low phosphorus use efficiency, while T. latifolia's strong rooting system enhanced soil exploration, with higher phosphorus use efficiency. Low growth rate, weak rooting system and low phosphorus uptake efficiency were account for the low phosphorus acquisition of S. sagittifolia and P. communis.Compared to T. latifolia, A. philoxeroides released more malic acid (27.33μmol·L-1) which was more efficient in phosphorus mobilization.The mini-rhizotron exprement and field study suggested that T. latifolia was efficient in the phosphorus retention with a strong root system. Although A. philoxeroides had high phosphorus uptake efficiency, the rhizosphere acification and phosphorus mobilization were significant. In conclusion, T. latifolia had a great potential to be used to in the wetland phosphorus retention, while A. philoxeroides should be avoided.
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