Phosphorus Mobilization in Bald Cypress Rhizospheres Grown in Wetland Soils.

Phosphorus release is commonly observed in fertilized fields that are restored to wetlands, but the exact mechanism causing the release is unknown for soils with small amounts of reducible Fe. This study examined the effects of dissolved organic carbon (DOC) and Fe reduction on P dissolution in the soil matrix and rhizospheres of bald cypress roots. Drained, partially saturated, and flooded hydrologies were established in bench-top rhizotrons containing bald cypress saplings planted in a Leon sand (sandy, siliceous, thermic Aeric Haplaquod). Pore water and soil samples of the rhizosphere and matrix were analyzed for chemical changes over time. In a preliminary study, rhizosphere measurements in flooded treatments had DOC concentrations of approximately 200 mg L^-1. Sixty-three days after saturation, rhizosphere DOC was significantly more (p=0.004) than matrix DOC with a mean difference of 57 mg L^-1. After 120 days of saturation that difference was not significant (p=0.143) indicating the DOC had migrated from the rhizosphere into the matrix. Phosphorus concentrations showed no significant difference in rhizosphere and matrix pore water after 98 days saturation. Phosphorus samples were not taken before this sampling during the beginning stages of ponding. These results are preliminary and additional work is in progress. However, it appears that P can be released in the rhizosphere of bald cypress roots by DOC production. Such release may lead to P loss from drained agricultural fields that are restored to wetlands.