Effects of Nitrogen Deposition on Nitrous Oxide Emissions from the Forest Floor

Abstract

Increasing nitrogen deposition due to human activity might have a serious impact on ecosystem functions such as the nitrogen transformations conducted by microbes. We therefore focused on nitrous oxide (N₂O) production as an indicator of soil microbial activity. The rates of N₂O emission from the forest floor were measured every two weeks in two forest stands in the central part of Japan: a red pine stand at Kannondai and a deciduous stand at Yasato. Nitrogen deposition rates by throughfall were 30.6 kg N ha⁻¹ y⁻¹ at Kannondai and 15.7 at Yasato. The rates of N₂O emission ranged from 0.5 to 14.2 µg N m⁻² h⁻¹ (mean 4.5) at Kannondai and from 0.2 to 7.0 µg N m⁻² h⁻¹ (mean 2.3) at Yasato. The N₂O emission rate showed significant positive relationships with soil temperature and nitrogen deposition during the preceding two weeks. The annual emission rates of N₂O were 0.38 kg N ha⁻¹ y⁻¹ at Kannondai and 0.20 at Yasato. As a the annual nitrogen deposition, these rates were 1.23% at Kannondai and 1.27% at Yasato.