Tree decline is a global concern, often with unknown primary causes. This study investigated the complex interactions between nitrogen (N) fluctuations, acidifying compounds, and soil microorganisms in relation to oak tree health. High-throughput sequencing and qPCR were used to analyze ammonia-oxidizing bacteria (AOB), archaea (AOA), and denitrifying communities in soils from declining and healthy oak trees. Results showed a higher AOB abundance in healthy trees, positively correlated with soil pH. AOA abundance was linked to lower NH₄⁺ concentrations. Denitrifier abundance was primarily influenced by the soil C:N ratio and correlated with AOB abundance regardless of tree health. The findings suggest that mitigating soil acidification by balancing C:N ratios could improve AOB abundance, influencing N transformations and potentially reducing stress on declining oak trees.

K. Scarlett, S. Denman, D. R. Clark, J. Forster, E. Vanguelova, N. Brown, C. Whitby