Natural 15 N abundance of ammonium and nitrate in soil profiles: New insights into forest ecosystem nitrogen saturation

作者：Geshere Abdisa Gurmesa, Erik A. Hobbie, Shasha Zhang, Ang Wang, Feifei Zhu, Weixing Zhu, Keisuke Koba, Muneoki Yoh, Chuankuan Wang, Qiuliang Zhang, Yunting Fang · 发表于：Ecosphere · 年份：2022 · DOI：10.1002/ecs2.3998 · 被引用次数：29 · 研究领域：Soil Carbon and Nitrogen Dynamics、Soil and Water Nutrient Dynamics、Peatlands and Wetlands Ecology

Abstract Assessment of nitrogen (N) saturation of forests is critical to the evaluation of the manner in which ecosystems will respond to current and future global changes such as N deposition. However, quantifying N saturation remains a challenge. We developed a conceptual model of N saturation stages in forest ecosystems based on (1) a hypothetical relative rate of ammonification, nitrification, and denitrification, (2) concentrations of ammonium and nitrate in the soil, and (3) 15 N enrichment pattern of bulk soil N, ammonium, and nitrate in the soil profile. We tested the hypotheses using data from forests located at five sites across eastern Asia. The fraction of nitrate in total inorganic N indicated that the sites represent an N saturation gradient with one boreal forest at stage 1 (least saturated), three temperate forests at stage 2, and one tropical forest at stage 3 (most saturated). The δ 15 N of bulk soil N increased from topsoil to subsoil more sharply at N‐limited sites than at the N‐rich sites along the N deposition gradient. We also found distinct 15 N enrichment patterns of bulk soil N, ammonium, and nitrate in the soil profile across the study sites. At stage 1, nitrate was more 15 N‐depleted than ammonium only in the organic soil horizon, indicating limited nitrification, while the 15 N depletion of nitrate to ammonium was observed in the deeper mineral soil at stages 2 and 3. Furthermore, ammonium was more 15 N‐depleted than bulk soil N at stages 1 and 2 ...