Main content area

Microbial denitrification dominates nitrate losses from forest ecosystems

Fang, Yunting, Koba, Keisuke, Makabe, Akiko, Takahashi, Chieko, Zhu, Weixing, Hayashi, Takahiro, Hokari, Azusa A., Urakawa, Rieko, Bai, Edith, Houlton, Benjamin Z., Xi, Dan, Zhang, Shasha, Matsushita, Kayo, Tu, Ying, Liu, Dongwei, Zhu, Feifei, Wang, Zhenyu, Zhou, Guoyi, Chen, Dexiang, Makita, Tomoko, Toda, Hiroto, Liu, Xueyan, Chen, Quansheng, Zhang, Deqiang, Li, Yide, Yoh, Muneoki
Proceedings of the National Academy of Sciences of the United States of America 2015 v.112 no.5 pp. 1470-1474
denitrification, drainage water, eutrophication, forest ecosystems, greenhouse gases, hypoxia, isotopes, leaching, nitrates, nitrogen, soil
Denitrification removes fixed nitrogen (N) from the biosphere, thereby restricting the availability of this key limiting nutrient for terrestrial plant productivity. This microbially driven process has been exceedingly difficult to measure, however, given the large background of nitrogen gas (N ₂) in the atmosphere and vexing scaling issues associated with heterogeneous soil systems. Here, we use natural abundance of N and oxygen isotopes in nitrate (NO ₃⁻) to examine dentrification rates across six forest sites in southern China and central Japan, which span temperate to tropical climates, as well as various stand ages and N deposition regimes. Our multiple stable isotope approach across soil to watershed scales shows that traditional techniques underestimate terrestrial denitrification fluxes by up to 98%, with annual losses of 5.6–30.1 kg of N per hectare via this gaseous pathway. These N export fluxes are up to sixfold higher than NO ₃⁻ leaching, pointing to widespread dominance of denitrification in removing NO ₃⁻ from forest ecosystems across a range of conditions. Further, we report that the loss of NO ₃⁻ to denitrification decreased in comparison to leaching pathways in sites with the highest rates of anthropogenic N deposition.