Nitrous oxide fluxes, their sources, and soil microbial communities depend more on carbon availability than long- and short-term phosphorus addition

Denitrification is the key process leading to production and loss of nitrogen gases from soils. Its main drivers are N availability and soil water content, but interactions with other elements, such as carbon and phosphorus, can also influence N₂O formation. So far, robust information on the effects of P and the historical context of P addition on N₂O sources remains limited. To address this knowledge gap, we conducted a mesocosm chamber experiment using isotopic approaches to investigate N transformations and N₂O sources following P fertilizer addition in soils with varying histories of P fertilization (low and high P). Differences in long-term fertilization affected C, N, and P availability as well as microbial community composition and nutrient cycling processes. Initially, microbes in both soils were C-limited with slightly higher C availability and microbial respiration in high P soils. Low P availability in low P soil did not restrict denitrification. In contrast, long-term P-unfertilized soil had higher N₂O losses compared to high P soil, which were further stimulated with P addition. Glucose addition alleviated C limitation and strongly promoted microbial growth and respiration, but did not affect N₂O emissions among treatments. Bacterial denitrification and nitrifier denitrification were the main N₂O forming processes, while dissimilatory nitrate reduction to ammonium (DNRA) contributed to NO₃⁻ reduction, but only slightly to N₂O formation.