Non-additive effects of Chinese fir leaf litter mixtures of different ages on soil N₂O emissions in a monoculture plantation treated with N and P additions

Litter decomposition is a fundamental process of global nutrient cycling that affects soil gas emissions, such as nitrous oxide (N₂O), which is a major greenhouse gas. However, it is unclear how mixing litter of different ages experiencing different nitrogen (N) and phosphorus (P) addition treatments affects litter decomposition rates and N₂O emissions. This limits our understanding of the mechanisms whereby litter input affects soil N₂O emissions.

Here, we studied the effects of mixing litter of Chinese fir (Cunninghamia lanceolata) of different ages (1 year and 2 year) on soil N₂O emissions and the underlying microbial mechanisms with a 100-day incubation experiment.

We found that mixing litter of different ages significantly lowered decomposition rates and soil N₂O emissions under the combination of high N and P addition. N addition directly increased soil N₂O emission rates (r = 0.32) and indirectly increased them via increasing soil NO₃^--N (r = 0.12). P and high N addition slowed litter mass loss and had a negative non-additive effect on soil N₂O emissions.

This study provides new insights into the effects of mixing litter of different ages on decomposition and soil N₂O emissions. In addition, it indicates that managing amounts and ratios of N and P additions in the context of stand age structure has the potential to mitigate soil GHG emissions.