The relative importance of denitrification and nitrate assimilation in midcontinental bogs

Denitrification rates measured in a Minnesota bog and a bog in western Ontario were similarly low (<0.20–2.28 µg m‒2 h‒1 as N). Nitrate addition stimulated denitrification at the Minnesota bog, but <1% of added NO3‒‐N (0.01–0.1 g m‒2) was denitrified in 24 h. In the Ontario bog, denitrification was not stimulated by NO3‒‐N application (0.08 g m‒2). Rates of NO3‒‐N uptake by Sphagnum, measured by nitrate reductase activity assays and NO3‒ disappearance from cultures, were much higher, 100–24,000 µg m‒2 h‒1 (0.57–48.7 µg g‒1 h‒1), than rates of denitrification at comparable NO3‒ loadings. Measurements of NO3‒ in pore water and moss throughfall confirm that NO3‒ disappears in the top 5–10 cm of moss. Plant uptake appears to be the dominant sink for NO3‒ in midcontinental bogs.