Effects of nitrogen deposition on nitrous oxide emissions from the forest floor

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 mug N m(-1)h(-1) (mean 4.5) at Kannondai and from 0.2 to 7.0 mug 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 percentage of the annual nitrogen deposition, these rates were 1.23% at Kannondai and 1.27% at Yasato.