Changes in soil pH and nutrient stoichiometry alter the effects of litter addition on soil nitrogen transformations and nitrous oxide emissions

Background and aims

Chinese-fir (Cunninghamia lanceolata) clonal varieties are used to establish fast-growing plantations in subtropical China and produce litters of varying quality. Litter serves as primary sources of carbon (C) and nitrogen (N) inputs to soils in forests and plays an important role in regulating soil N transformations, including N losses via nitrous oxide (N₂O) emissions. However, little is known about the effects of litter addition from different Chinese-fir clones on soil N dynamics.

Methods

We conducted an aerobic incubation experiment to investigate net rates of N mineralization (NMR) and nitrification (NNR) and N₂O emissions in soils from seven forests planted with different Chinese-fir clones as affected by litter addition at the rates of 0, 0.3%, 0.6%, and 0.9% of dry soil weight.

Results

Both NMR and NNR decreased linearly with increasing litter addition rate, while soil respiration and N₂O emissions exhibited the opposite, regardless of the clonal treatment. In addition, NMR and NNR, expressed as mg N per g carbon (C) applied, either decreased or increased logarithmically with increasing soil pH and C to phosphorus (P) ratio, respectively. Structural equation modeling showed that litter properties (i.e., C/N and total P content) drive NMR and NNR by influencing soil respiration, pH, and nutrient stoichiometry. However, the response of N₂O emissions to litter addition is not associated with either soil or litter properties.

Conclusions

Our findings indicate that effects of adding litter from Chinese-fir clones on soil N transformations are dependent on edaphic factors, which are primarily influenced by litter quality.