Loss and assimilation of 15N-nitrate added to a North Dakota cattail marsh

Abstract

Field 15N balance studies were conducted to determine the fate of K 15NO 3 added during summer to surface water in 0.27 m 2 plots within a North Dakota cattail (a mixture of Typha glauca Godr. and Typha angustifolia L.) marsh. In a 1989 study, 50.4 mmol 15NO 3 −-N (approximately 1.1 mmol NO 3 − 1 −1) disappeared within 8 days after a temporary build-up of NO 2 −-N. Approximately 42% of the applied 15N remained in the marsh. This residual N was found in cattail roots and rhizomes (9.5%), floating plants ( Lemna minor L. and Spirodela polyrhiza (L.) Schleiden) (8.9%), soil (8.3%), litter (6.9%), surface water (4.6%) and cattail shoots (4.1%). The missing 15N (58%) was presumably lost as a result of denitrification. In a 1991 experiment, 50.4 mmol of K 15NO 3 was added to plots which had previously received additions of deionized water or 153 mmol of unlabeled KNO 3. All the labeled NO 3 − again disappeared within 8 days. The unaccounted-for 15N was approximately 56% and 82% of the added K 15NO 3-N in plots without and with the antecedent unlabeled KNO 3 treatment, respectively. The difference in recovery (26%) was highly significant. Stimulation of dissimilatory NO 3 − and NO 2 − reductases and/or suppression of dissimilatory reduction of 15NO 3 − to 15NH 4 + are postulated as likely factors for the higher apparent denitrification loss associated with the antecedent KNO 3 treatment.