Organic matter stability in temperate forest soils is affected by tree species identity but not by litter quality

Temperate forest soils have a great potential to store carbon (C) and mitigate climate change. However, the quality of litter inputs to the soil differs significantly between tree species, which can potentially affect the proportions of the less protected particulate organic matter (POM) and more protected mineral-associated OM (MAOM) fractions.

Here, we performed field observations of the soil OM (SOM) fraction quantities in deciduous (beech), mixed and coniferous (spruce) forest stands in the mineral top (0–10 cm) and subsoil (50–60 cm) horizons during the whole growing season and related it to leaf and root litter quality.

We found higher proportions of C and N in the POM fraction in coniferous stands and higher proportions of C and N in the MAOM fraction in deciduous stands. The differences in SOM stability were only apparent in the topsoil, with the subsoil showing generally high proportions of C and N in the MAOM regardless of the tree species. The differences in the C and N proportions in SOM fractions were, however, not related to leaf and/or root litter quality.

The results indicate that the tree species has a distinct effect on the SOM stability in the topsoil, but not in the subsoil, and that factors other than litter quality connected to the tree species identity govern OM formation in forest soils.