Data for: Assessing above and belowground recovery from ammonium sulphate addition and wildfire in a lowland heath: mycorrhizal fungi as potential indicators.

Atmospheric pollution containing soil-nitrifying ammonium sulphate ((NH4)2SO4) affects semi-natural ecosystems worldwide. Long-term additions of (NH4)2SO4 to nitrogen(N)-limited habitats, including heathlands, increase climate stress affecting recovery from wildfires. Although heathland vegetation largely depends on ericoid mycorrhizal fungi (ErM) to access soil N, we lack a detailed understanding of how prolonged exposure to (NH4)2SO4 may alter ErM community composition and host plants’ reliance on fungal partners following wildfire and affect recovery. Simulation of atmospheric pollution ((NH4)2SO4) occurred bi-weekly for 5 years after a 2006 wildfire in a UK heathland. Ten years after treatments ceased, we measured vegetation structure, lichen and lichen photobiont composition, soil characteristics, ErM colonisation, ErM diversity in roots and soil, and assessed ErM potential as novel recovery indicators. Heather height and density, and moss groundcover, were greater in N-enriched plots. Lichen community indices showed significant treatment effects but without differences in photobionts. Soil pH and Mg were significantly lower in treated plots while soil cation exchange capacity was significantly higher. There were no detectable differences in ErM composition and keystone ErM taxa between control and treated plots. Soil carbon stock measures were variable. Our results indicate atmospheric pollution following fire can have significant lingering effects above- and belowground. ErM diversity and root colonization were not assessed in the original N-addition experiment; we advocate for their inclusion in future studies as an integral part of the recovery assessment toolkit. We show that mycorrhizal fungi diversity is a viable ecological tool and summarise key steps for ErM identification.

Methods
Total soil DNA was extracted in duplicates from 0.25 g of soil from each plot (two extractions per plot, n = 24, DNeasy PowerSoil Kit). The DNA extractions were processed by Macrogen (Seoul, South Korea) for library preparation and Illumina sequencing with the primer set ITS86F and ITS4 (White et al. 1990; Turenne et al. 1999) targeting the ITS2 region.