Erguna Forest-Steppe Ecotone Ecosystem Research Station, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, PR China.
Erguna Forest-Steppe Ecotone Ecosystem Research Station, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, PR China; College of Environmental Science and Engineering, Yangzhou University, Yangzhou, 225127, PR China.
J Environ Manage. 2024 Jun;362:121293. doi: 10.1016/j.jenvman.2024.121293. Epub 2024 Jun 4.
Soil acidification induced by reactive nitrogen (N) inputs is a major environmental issue in grasslands, as it lowers the acid neutralizing capacity (ANC). The specific impacts of different N compound forms on ANC remain unclear. Grassland management practices like mowing and grazing can remove a considerable amount of soil N and other nutrients, potentially mitigating soil acidification by removing N from the ecosystem or aggravating it by removing base cations. However, empirical evidence regarding the joint effects of adding different forms of N compounds and mowing on ANC changes in different-sized soil aggregates is still lacking. This study aimed to address this knowledge gap by examining the effects of three N compounds (urea, ammonium nitrate, and ammonium sulfate) combined with mowing (mown vs. unmown) on soil ANC in different soil aggregate sizes (>2000 μm, 250-2000 μm, and <250 μm) through a 6-year field experiment in Inner Mongolia grasslands. We found that the average decline in soil ANC caused by ammonium sulfate (AS) addition (-78.9%) was much greater than that by urea (-25.0%) and ammonium nitrate (AN) (-52.1%) as compared to control. This decline was attributed to increased proton (H) release from nitrification and the leaching of exchangeable Ca and Mg. Mowing aggravated the adverse effects of urea and AN on ANC, primarily due to the reduction in soil organic matter (SOM) contents and the removal of exchangeable Ca, K, and Na via plant biomass harvest. This pattern was consistent across all aggregate fractions. The lack of variation in soil ANC among different soil aggregate fractions is likely due to the contrasting trend in the distribution of exchangeable Ca and Mg. Specifically, the concentration of exchangeable Ca increased with increasing aggregate size, while the opposite was true for that of exchangeable Mg. These findings underscore the importance of considering the forms of N compounds when assessing the declines of ANC induced by N inputs, which also calls for an urgent need to reduce N emissions to ensure the sustainable development of the meadow ecosystems.
由于氮（N）输入引起的土壤酸化是草原的一个主要环境问题，因为它降低了酸中和能力（ANC）。不同 N 化合物形式对 ANC 的具体影响尚不清楚。割草和放牧等草原管理措施可以去除大量土壤 N 和其他养分，通过从生态系统中去除 N 或通过去除碱基阳离子来减轻土壤酸化，从而潜在地减轻土壤酸化。然而，关于不同形式的 N 化合物和割草对不同大小土壤团聚体 ANC 变化的联合效应的实证证据仍然缺乏。本研究旨在通过在内蒙古草原进行的为期 6 年的田间试验，研究三种 N 化合物（尿素、硝酸铵和硫酸铵）与割草（割草与未割草）相结合对不同土壤团聚体大小（>2000μm、250-2000μm 和 <250μm）土壤 ANC 的影响，以填补这一知识空白。我们发现，与对照相比，添加硫酸铵（AS）导致的土壤 ANC 平均下降（-78.9%）远大于尿素（-25.0%）和硝酸铵（AN）（-52.1%）。这种下降归因于硝化作用产生的质子（H）释放和可交换 Ca 和 Mg 的淋失。割草加剧了尿素和 AN 对 ANC 的不利影响，主要是由于植物生物量收获导致土壤有机质（SOM）含量降低和可交换的 Ca、K 和 Na 的去除。这种模式在所有团聚体分数中都是一致的。不同土壤团聚体分数之间土壤 ANC 没有变化，可能是由于可交换 Ca 和 Mg 的分布趋势相反。具体而言，可交换 Ca 的浓度随团聚体尺寸的增加而增加，而可交换 Mg 的浓度则相反。这些发现强调了在评估 N 输入引起的 ANC 下降时考虑 N 化合物形式的重要性，这也迫切需要减少 N 排放以确保草地生态系统的可持续发展。
