Soil cores of 8cm diameter and depth were collected from each plot near the base of Calluna vulgaris on the 1st April 2015, then transported back to Bangor at 4°C. Cores were cut from the top into 1 cm deep subsections. Each subsection was soaked and agitated to break up the root/soil clumps. Roots confidently identified as C. vulgaris were removed by hand and thoroughly washed in tap water. Necrotic or rotting roots were discarded. WinRHIZO version 3.2 was used to measure the length and diameter of cleaned subsection roots on a flatbed scanner. Roots were positioned without overlapping, submerged in 5 mm tap water to improve scanning accuracy. Acquisition parameters were set using the TWAIN interface in professional mode: positive film, 24 bit and 300 dpi. Post scanning, ten of the finest roots were manually selected from each subsection for microscopic investigation. The remaining roots were oven dried at 70°C for 24 hours, producing dry weight data for those < and > 2mm in diameter. All core fragments for microscopic assessment were soaked over 20 hours in 10% Potassium hydroxide (KOH). Roots were thoroughly rinsed in deionised water and heated in a water bath at 90°C for 15 minutes in 5% vinegar-ink solution. Roots were rinsed in three changes of tap water, acidified and de-stained by soaking in tap water with a few drops of vinegar for a further 20 minutes. A compound microscope was used to estimate proportional colonisation using the magnified intersection technique, with a scale bar cuticle instead of cross-hair and at a 40x magnification. Roots were cut approximately 1-2 cm in length, with 2 mm passes made along each root length. All cortical cells were examined for Ericoid mycorrhizae (ErM) and dark septate endophyte (DSE), working through the plane of focus. Each interval was categorised based upon ErM colonisation into 0 %, < 1 %, < 10 %, < 50 %, > 50 % and > 90 % colonisation. Data were transferred into an Excel spreadsheet. Data were exported as a comma separated value file for ingestion into the EIDC.

This dataset contains root length, biomass and fungal colonisation data for Calluna vulgaris from control, drought and warming treated soils from the long term climate change experiment in Clocaenog forest. Soil samples were collected from the climate change experiment in Northeast Wales during April 2015. Roots were separated from the soil, their length and biomass measured and then analysed using microscopy for Ericoid mycorrhizae (ErM) and dark septate endophyte (DSE) colonisation of Calluna vulgaris. The experimental field site consists of three untreated control plots, three plots where the plant canopy air is artificially warmed during night time hours and three plots where rainfall is excluded from the plots at least during the plants growing season (March to September). The Climoor field experiment intends to answer questions regarding the effects of warming and drought on ecosystem processes and has been running since 1999. The root length and fungal colonisation data aims to understand how changes in soil hydrological and chemical properties have influenced Calluna vulgaris rooting behaviour and interactions with the soil microbiome. This work was supported by the Natural Environment Research Council award number NE/R016429/1 as part of the UK-SCAPE programme delivering National Capability.