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Boreal forests are ecosystems with low nitrogen N availability that store globally significant amounts of carbon C , mainly in plant biomass and soil organic matter SOM. Although crucial for future climate change predictions, the mechanisms controlling boreal C and N pools are not well understood. Here, using a three-year field experiment, we compare SOM decomposition and stabilization in the presence of roots, with exclusion of roots but presence of fungal hyphae and with exclusion of both roots and fungal hyphae.
Roots accelerate SOM decomposition compared to the root exclusion treatments, but also promote a different soil N economy with higher concentrations of organic soil N compared to inorganic soil N accompanied with the build-up of stable SOM-N. In contrast, root exclusion leads to an inorganic soil N economy i. Based on our findings, we provide a framework on how plant roots affect SOM decomposition and stabilization.
Boreal forests are key components of the global carbon C cycle due to their high C storage and enormous potential for C sequestration into soil organic matter SOM 1. Nevertheless, with climate change SOM decomposition might increase shifting boreal forests from C sinks to C sources, thereby accelerating global warming 1.
The mechanisms behind accumulation and stabilization of SOM in boreal forest soils are poorly understood but essential for predicting C stocks in a future climate 2. The boreal forest C storage is tightly linked to the nitrogen N cycle 3 , which is characterized by the binding or complexation of a large fraction of soil N to other soil compounds such as minerals and polyphenols, resulting in low N availability 4 , 5 , 6 , 7 , 8.
