The relative importance of denitrification and nitrate assimilation in midcontinental bogs

Abstract

Denitrification rates measured in a Minnesota bog and a bog in western Ontario were similarly low (<0.20–2.28 µ g m ‒2 h ‒1 as N). Nitrate addition stimulated denitrification at the Minnesota bog, but <1% of added NO 3 ‒ ‐N (0.01–0.1 g m ‒2 ) was denitrified in 24 h. In the Ontario bog, denitrification was not stimulated by NO 3 ‒ ‐N application (0.08 g m ‒2 ). Rates of NO 3 ‒ ‐N uptake by Sphagnum, measured by nitrate reductase activity assays and NO 3 ‒ disappearance from cultures, were much higher, 100–24,000 µ g m ‒2 h ‒1 (0.57–48.7 µ g g ‒1 h ‒1 ), than rates of denitrification at comparable NO 3 ‒ loadings. Measurements of NO 3 ‒ in pore water and moss throughfall confirm that NO 3 ‒ disappears in the top 5–10 cm of moss. Plant uptake appears to be the dominant sink for NO 3 ‒ in midcontinental bogs.