School of Earth System Science, Tianjin University, Tianjin 300072, China.
School of Earth System Science, Tianjin University, Tianjin 300072, China.
Sci Total Environ. 2022 Sep 10;838(Pt 3):156405. doi: 10.1016/j.scitotenv.2022.156405. Epub 2022 Jun 2.
To examine the perturbation of atmospheric nitrogen (N) deposition on soil N status and the biogeochemical cycle is meaningful for understanding forest function evolution with environmental changes. However, levels of soil bioavailable N and their environmental controls in forests receiving high atmospheric N deposition remain less investigated, which hinders evaluating the effects of enhanced anthropogenic N loading on forest N availability and N losses. This study analyzed concentrations of soil extractable N, microbial biomass N, net rates of N mineralization and nitrification, and their relationships with environmental factors among 26 temperate forests under the N deposition rates between 28.7 and 69.0 kg N ha yr in the Beijing-Tianjin-Hebei (BTH) region of northern China. Compared with other forests globally, forests in the BTH region showed higher levels of soil bioavailable N (NH, 27.1 ± 0.8 mg N kg; NO, 7.0 ± 0.8 mg N kg) but lower net rates of N mineralization and nitrification (0.5 ± 0.1 mg N kg d and 0.4 ± 0.1 mg N kg d, respectively). Increasing N deposition levels increased soil nitrification and NO concentrations but did not increase microbial biomass N and N mineralization among the study forests. Soil moisture and C availability were found as dominant factors influencing microbial N mineralization and bioavailable N. In addition, by budgeting the differences in soil total N densities between the 2000s and 2010s, atmospheric N inputs to the forests were more retained in soils than lost proportionally (84% vs. 16%). We concluded that the high N deposition enriched soil N without stimulating microbial N mineralization among the study forests. These results clarified soil N status and the major controlling factors under high anthropogenic N loading, which is helpful for evaluating the fates and ecological effects of atmospheric N pollution.
为了探究大气氮（N）沉降对土壤 N 状况和生物地球化学循环的干扰，理解森林功能随环境变化的演变具有重要意义。然而，在受到高大气 N 沉降的森林中，土壤生物可利用 N 的水平及其环境控制因素仍研究较少，这阻碍了评估人为 N 加载增强对森林 N 有效性和 N 损失的影响。本研究分析了中国北方京津冀地区 N 沉降率为 28.7-69.0 kg N ha yr 之间的 26 个温带森林中土壤可提取 N、微生物生物量 N、净氮矿化和硝化速率及其与环境因子的关系。与全球其他森林相比，京津冀地区的森林具有更高的土壤生物可利用 N（NH，27.1±0.8 mg N kg；NO，7.0±0.8 mg N kg），但净氮矿化和硝化速率较低（0.5±0.1 mg N kg d 和 0.4±0.1 mg N kg d）。增加 N 沉降水平会增加土壤硝化作用和 NO 浓度，但不会增加研究森林中的微生物生物量 N 和氮矿化作用。土壤水分和 C 供应被认为是影响微生物氮矿化和生物可利用 N 的主要因素。此外，通过预算 2000 年代和 2010 年代土壤总 N 密度之间的差异，大气 N 输入到森林的量比损失的量更多地保留在土壤中（84%比 16%）。我们的结论是，高 N 沉降在研究森林中增加了土壤 N 而没有刺激微生物氮矿化。这些结果阐明了在高人为 N 加载下土壤 N 状况和主要控制因素，有助于评估大气 N 污染的命运和生态效应。
