Interactive effects of plant litter chemistry and organic/inorganic forms of nitrogen addition on Moso bamboo (Phyllostachys edulis) soil respiration

The impact of plant litter on soil carbon (C) cycling is influenced by external nitrogen (N) deposition and plant litter chemistry. While previous research has mainly focused on inorganic N deposition and its effect on plant litter decomposition and soil C cycling, the influence of organic N remains poorly understood. In this study, we conducted a 180-day incubation experiment to investigate how different N forms (NH₄NO₃, Urea 50% + Glycine 50%) and litter chemistry (varying lignin/N ratios) affect CO₂ emissions from an acidic Moso bamboo (Phyllostachys edulis) forest soil. Our findings indicate that litter addition increased soil CO₂ emissions and the proportion of CO₂-C to Total C (considering added litter-C as a part of total C). Specifically, Moso bamboo leaf litter with a lower lignin/N ratio led to higher soil CO₂ emissions and CO₂-C/Total C ratios. The combined addition of litter and N exhibited an antagonistic effect on soil CO₂ emissions, with inorganic N having a more pronounced effect compared to organic N. This antagonistic effect was attributed to the N addition-induced soil acidification, thereby inhibiting microbial activities and reducing soil respiration promoted by litter input. This effect was confirmed by random forest analysis and partial least squares path modeling, which further identified soil dissolved organic C and pH as critical factors positively influencing soil CO₂ emissions. Overall, our study suggests that atmospheric N deposition can mitigate litter-induced soil CO₂ emissions, particularly under inorganic N forms and when leaf litters with high lignin/N ratios are introduced.