Indirect effects of soil warming on litter decomposition via changes in litter quality of dominant tree species in three cool-temperate forests

Background and aims

Soil warming influences decomposition not only through direct changes in the soil environment, but also by modifying litter quality. We tested the indirect effects by examining whether warming-induced changes in soil nitrogen (N) mineralization rates affect litter quality and decomposition.

Methods

Soil warming experiments were conducted in three forests characterized by differing snow depths. Soil N dynamics and leaf litter quality were measured after 5–8 years of warming. Following this warming treatment, a 2-year litter-bag experiment was performed.

Results

Soil warming affected soil N dynamics and the litter carbon-to-nitrogen (C: N) ratio, with varying effects across forests. The parameters of N dynamics during the growing season correlated with the C: N ratio of litter across the three forests; in the shallow snow forest, winter N dynamics were also related. Unlike the other two forests where the snowpack prevents soil freezing, freezing occurs in the shallow snow forest. When warming prevents freezing, ammonia production is suppressed in winer, associated with a higher C: N ratio in the litter. Additionally, in our study, soil warming decreased phenol concentrations in the shallow snow forest. Multiple regression analysis indicated that phenol concentration and C: N ratio in the litter were critical to decomposition, particularly during the early phase. Among litter traits, phenol concentration emerged as the strongest predictor of decomposition.

Conclusion

Soil warming changes litter quality, linked to changes in soil N dynamics, potentially affecting decomposition rates. This reveals indirect effects of soil warming and underscore the impacts on ecosystem processes through plant-soil interactions.