Work

Nitrogen fertilisation of boreal forest soil increases soil carbon pool through elevated microbial necromass formation but also modifies tree secondary metabolism

Year: 2025

Type: article

Abstract: Forests contain significant amounts of the global carbon (C) pool with the major fraction stored belowground. Nitrogen (N) fertilisation of forest soils may increase biomass production and soil organic C pools, providing a strategy for climate change mitigation. Here we aimed to elucidate the mechanisms behind the increase in soil C due to N addition using a long–term fertilisation experiment on a Scots pine stand with a combination of chemistry, microbiology and greenhouse gas fluxes. Our results showed that N fertilisation increased C stocks, microbial biomass, necromass and the activity of extracellular enzymes, with no significant increase in greenhouse gas production. Moreover, N fertilisation decreased the production of a group of plant secondary metabolites, tannins. These profound changes were observed in the organic layer of the soil, and differences in mineral soil were less detectable. Mechanistically, N fertilisation increased the C stock via elevated litter input and higher transfer of root C to soil microorganisms increasing fungal biomass and further necromass, which was stabilised in the soil. Our study supports the view that management strategies to increase microbial necromass in persistent C pools could lead to elevated C stabilisation, though caution should be taken regarding potential changes in plant metabolism.

Source: Soil Biology and Biochemistry

DOI: 10.1016/j.soilbio.2025.109917