Ammonia emissions from a poultry farm drive changes in soil biogeochemistry and microbial communities along a treebelt in northern England

Agriculture is responsible for 87 % of ammonia (NH₃) emissions in the UK, mostly from concentrated point sources, contributing to the exceedance of critical nitrogen deposition concentrations. Treebelts (also known as shelterbelts) can be planted around emission sources to intercept NH₃ and reduce its drift. This study examined how atmospheric NH₃ concentration affects soil biogeochemistry, and the composition and richness of fungal and bacterial communities beneath a 13-year-old treebelt on a poultry farm in Cumbria, UK. We measured tree growth and analysed soil samples collected at varying distances from the poultry housing to evaluate the effect of NH₃ concentration. Under the highest NH₃ concentration, soil pH decreased by 13 % (p < 0.001), six out of the nine nutrients we examined decreased significantly (p < 0.05), while soil organic carbon was 29 % higher under the greatest NH₃ concentration within the treebelt (p < 0.05). The community composition of soil fungi and bacteria (based on ITS, LSU, and 16S amplicon sequencing) changed significantly with NH₃ concentration (p < 0.001), driven mainly by soil pH, phosphate, C/N ratio and ammonium (plus nitrate for bacteria). Genus richness of arbuscular mycorrhizal fungi, saprotrophic fungi, and bacteria were 80 %, 9 %, and 13 % lower respectively under the highest NH₃ concentration (p < 0.05). Overall, higher NH₃ concentrations closer to the poultry housing significantly altered soil chemistry and microbial community composition, and reduced richness, highlighting the importance of understanding NH₃ impacts on soil ecology when using treebelts to capture emissions.