Canopy and understory nitrogen additions differentially regulate soil organic carbon fractions via litter–microbe–mineral interactions

作者：Youchao Chen, Q. Liu, Xinli Chen, Ji Chen, Biao Zhu, Shenglei Fu, Scott X. Chang, Yanjiang Cai · 发表于：Forest Ecosystems · 年份：2025 · DOI：10.1016/j.fecs.2025.100410 · 被引用次数：5 · 研究领域：Soil Carbon and Nitrogen Dynamics、Mycorrhizal Fungi and Plant Interactions、Biocrusts and Microbial Ecology

The effects of nitrogen (N) deposition on forest soil organic carbon (SOC) are largely unclear, likely due to the divergent responses of particulate (POC) and mineral-associated carbon (MAOC). Conventional understory inorganic N (UIN) additions neglect canopy processes and the impacts of organic N, potentially misevaluating N deposition effects. This study was conducted in a long-term N addition experiment established in a Moso bamboo forest, which included six treatments combining canopy and understory N additions with organic (urea + glycine) and inorganic (NH 4 NO 3 ) forms at a rate of 50 kg·N·ha −1 ·yr −1 . Litterbags were installed for a two-year decomposition experiment and collected at quarterly intervals, together with concurrent soil sampling under litterbags at 0–10 cm depth. We aimed to examine the effects of canopy vs. understory N addition and organic vs. inorganic N form on soil POC and MAOC concentrations. Our results showed that canopy N additions significantly reduced POC (−15.9%) but did not affect MAOC ( P > 0.05). Conversely, understory N additions significantly increased POC (+30.9%) and decreased MAOC (−28.9%). Canopy N additions decreased POC by enhancing peroxidase activity and fungal diversity (FuD), while understory N additions promoted POC by inhibiting litter decomposition. Additionally, understory N addition-induced soil acidification decreased soil Ca 2+ concentration, microbial carbon use efficiency, and bacterial necromass C, as well as the re...