TY  - JOUR
AU  - Chen, Youchao
AU  - Liu, Qinxi
AU  - Chen, Xinli
AU  - Chen, Ji
AU  - Zhu, Biao
AU  - Fu, Shenglei
AU  - Chang, Scott X.
AU  - Cai, Yanjiang
PY  - 2026
TI  - Canopy and understory nitrogen additions differentially regulate soil organic carbon fractions via litter–microbe–mineral interactions
JO  - Forest Ecosystems
SN  - 2095-6355
VL  - 15
IS  - 1
AB  - 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 (NH4NO3) 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 Ca2+ concentration, microbial carbon use efficiency, and bacterial necromass C, as well as the release of litter water-soluble compounds, thereby inhibiting MAOC. Moreover, nitrogen forms (organic vs. inorganic) had no effect on SOC fractions. Our findings underscore that canopy and understory N addition approaches differentially regulate SOC fractions by altering litter decomposition–microbial–mineral interactions, and the understory approach may overestimate soil POC gain and MAOC loss driven by atmospheric N deposition.
UR  - https://doi.org/10.1016/j.fecs.2025.100410
DO  - 10.1016/j.fecs.2025.100410