LOSS AND UPTAKE OF15N-AMMONIUM IN SUBMERGED SOILS OF A CATTAIL MARSH

The uptake, distribution, and recovery of nitrogen by field populations of T. latifolia L. (cattails) were determined using (¹⁵NH₄)₂SO₄. The results show that 75.3% (53.6% in the plant and 21.7% in the soil) of the isotopically labeled nitrogen added to sampling cylinders containing a single cattail plant could be recovered at the end of one growing season, whereas only 34.6% could be recovered from control cylinders. The increased recovery of ¹⁵NH₄⁺-nitrogen in cylinders containing actively growing T. latifolia compared to cylinders not containing plants suggests that T. latifolia rapidly assimilates labeled nitrogen before it is lost via denitrification or uptake by free-living soil microorganisms. Measurements of redox potentials in a 60-cm-deep field core planted or not planted with T. latifolia showed that only the top 2 and 5 cm of the water column was oxidized (greater than 200 mv at pH 7), respectively. The remaining 58 and 55 cm of the column, including the soil-water interface, was reduced (less than 200 mv at pH 7). The presence or absence of actively growing T. latifolia plants in the soil cores did not appear to alter significantly the redox profile. The presence of an oxidized zone overlying a reduced zone in cores collected from the field indicates that a portion of the ¹⁵NH₄⁺-nitrogen added to cylinders during the field experiment may have been lost through nitrification-denitrification reactions.