Soil nitrification increases with elevated phosphorus or soil pH in an acidic mixed mesophytic deciduous forest

The role of phosphorus (P) mediating nitrogen (N) transformation processes is poorly understood which raises an important question: Does P, like soil pH, have a strong control in altering the cycling of soil N? From 2010 to 2018, pH and/or P availability was elevated with lime and P fertilizer in three mixed mesophytic deciduous forests on the unglaciated portion of the Allegheny Plateau, southeast Ohio, USA. We hypothesized that in addition to soil pH, P addition can influence the cycling of soil N because both can change N dynamics, which can alter nitrification rates. Increasing soil pH increased nitrification and nitrate pools by 30 and 4 times, respectively during the growing season. Furthermore, elevating P also stimulated nitrification and increased soil nitrate pools by 10 and 2 times, respectively. However, the influence of raising soil pH on nitrification was diminished when combined with P addition. Results suggest that N biogeochemical processes are sensitive to P availability, but the mechanistic nature of this relationship appears complex with unclear feedback systems regulating nitrification rates from these deciduous forests.