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<p>Although the effects of nitrogen (N) and water addition on carbon (C) and nutrient dynamics have been extensively investigated in surface soils of grassland ecosystems, the responses of different fractions of soil organic matter in subsoils —the primary reservoirs of elemental storage—to N and water inputs remain poorly understood. We evaluated organic C and six mineral elements (N, K, Ca, Mg, Fe, Mn) in bulk soil, particulate organic matter (POM), and mineral-associated organic matter (MAOM) at 0–10&#xa0;cm (topsoil), 30–40&#xa0;cm (upper subsoil), and 60–80&#xa0;cm (deep subsoil) in a Eurasian steppe after long-term N and water addition. Although soil organic carbon (SOC) and total nitrogen (TN) concentrations were 3–4 times higher in POM (including free and occluded forms) than in MAOM, over 70% of total C and N stocks across the three soil depths were stored in MAOM, due to its greater mass. Similarly, total K, Ca, Mg, Fe, and Mn were predominantly stored in coarse MAOM (≥ 20&#xa0;µm), while total Mg was mainly associated with fine MAOM (&lt; 20&#xa0;μm). Additions of N and water significantly altered the distribution of SOC and mineral elements among soil fractions, with effects varying by depth. The stimulatory effects on SOC and TN were most pronounced in topsoil and upper subsoil. Greater changes in total K, Ca, Mg, Fe, and Mn concentrations or stocks occurred in fine MAOM than in coarse MAOM. Key drivers of SOC and TN distribution varied with soil depth, with soil available N and total K, Fe, Ca, and Mg concentrations in fine MAOM identified as major influencing factors. These findings highlight the critical role of mineral-associated processes, particularly in fine fractions, in shaping soil C and N dynamics in grassland ecosystems.</p> Graphical Abstract <p></p>

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Dynamics of Multiple Elements in Particulate and Mineral-Associated Organic Matter Across Varying Soil Depths Following 13 years of Nitrogen and Water Addition in an Agro-Pastoral Ecotone Grassland

  • 期刊论文

  • 发表日期：

    2026年3月19日

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  • Huiqi Ke,
  • Shilin Wang,
  • Guoxiang Niu,
  • Ruzhen Wang,
  • Yibo Li,
  • Yanan Ning,
  • Canran Yang,
  • Yinliu Wang,
  • Yong Jiang,
  • Jianhui Huang

摘要

Although the effects of nitrogen (N) and water addition on carbon (C) and nutrient dynamics have been extensively investigated in surface soils of grassland ecosystems, the responses of different fractions of soil organic matter in subsoils —the primary reservoirs of elemental storage—to N and water inputs remain poorly understood. We evaluated organic C and six mineral elements (N, K, Ca, Mg, Fe, Mn) in bulk soil, particulate organic matter (POM), and mineral-associated organic matter (MAOM) at 0–10 cm (topsoil), 30–40 cm (upper subsoil), and 60–80 cm (deep subsoil) in a Eurasian steppe after long-term N and water addition. Although soil organic carbon (SOC) and total nitrogen (TN) concentrations were 3–4 times higher in POM (including free and occluded forms) than in MAOM, over 70% of total C and N stocks across the three soil depths were stored in MAOM, due to its greater mass. Similarly, total K, Ca, Mg, Fe, and Mn were predominantly stored in coarse MAOM (≥ 20 µm), while total Mg was mainly associated with fine MAOM (< 20 μm). Additions of N and water significantly altered the distribution of SOC and mineral elements among soil fractions, with effects varying by depth. The stimulatory effects on SOC and TN were most pronounced in topsoil and upper subsoil. Greater changes in total K, Ca, Mg, Fe, and Mn concentrations or stocks occurred in fine MAOM than in coarse MAOM. Key drivers of SOC and TN distribution varied with soil depth, with soil available N and total K, Fe, Ca, and Mg concentrations in fine MAOM identified as major influencing factors. These findings highlight the critical role of mineral-associated processes, particularly in fine fractions, in shaping soil C and N dynamics in grassland ecosystems.

Graphical Abstract