The data are derived from Alnus glutinosa plants grown in intact soil cores collected from beneath three co-occurring tree species. The data describe plant above and below ground biomass, coarse and fine root biomass, colonisation of roots by Frankia and ectomycorrhizal fungi, ecosystem carbon fluxes, capture of 13C from a pulse labelling process, 15N content of leaves, and soil nutrients. Full details about this nonGeographicDataset can be found at https://doi.org/10.5285/8816a55a-0e2e-4414-872f-3575170585dc

The data encompass measurements in soil and litter, including leaf litter decomposition, soil respiration, and root morphology analysis in the absence and presence of tree roots in the UK. Data were collected in two locations, Alice Holt and Thetford, UK, in October-November 2023, under three different treatments: 1. Root trenching and root ingrowth prevention: roots were severed from the tree in a 2x2 meter area, and a membrane preventing root ingrowth was inserted into the soil, resulting a free of living space. 2. Root trenching: roots were severed from the tree in a 2x2 meter area, but new roots were allowed to grow in that space. 3. Control: The soil remained undisturbed, with no intervention. Full details about this dataset can be found at https://doi.org/10.5285/a912c7d5-6f74-4ee8-b192-b414694025b4

Seedlings were grown in soil collected from an experiment at Hambleton Forest, North Yorkshire. Soils originated from plots containing either Scots pine or birch monocultures, or a mixture of both species. In the lab, pairs of seedlings of birch and Scots pine were grown as monocultures and mixtures from each of the three plot treatments. The data represent the biomass, leaf C:N ratio and mycorrhizal status determined after 20 weeks. Full details about this dataset can be found at https://doi.org/10.5285/7991871e-382f-422f-b5b2-91b4f6d8598f