Dynamics of soil N2O fluxes and hot-moments typification: How are they related to environmental characteristics?

To date, extensive field measurements of nitrogen oxide (N2O) exchanges in soils across diverse terrestrial ecosystems, complemented by controlled laboratory incubation studies, have unveiled considerable variability in N2O soil fluxes. This variability arises from the intricate interplay of various factors. Notably, soil N2O emissions display significant spatiotemporal fluctuations, including extreme events. The primary objective of this study is to enhance our understanding of the environmental factors influencing soil N2O fluxes and to characterize instances of pronounced N2O emissions, hereafter termed "hot-moments." Our investigation encompassed six distinct sites of the Integrated Carbon Observation System (ICOS) network including agricultural systems, sylvicultural systems, and unmanaged forests spanning the northern hemisphere. To identify and categorize hot-moments events, we standardized N2O values and considered events greater than or equal to 4, or -4-fold standard deviations from the mean of each site. We then conducted wavelet coherence analyses to delve into the patterns of N2O fluxes. In the biwavelet plots, our variable of interest was juxtaposed with each soil environmental variable, illustrating the distribution of correlations in the time-frequency domain of our signals. Employing this advanced approach, we explored N2O patterns and their variability in relation to specific environmental characteristics (soil water content, soil temperature, and CO2 flux) within the six temporal series (different soil types). Our analyses revealed a recurring pattern across all time series, with a frequency of approximately 24 hours for the N2O vs. CO2 plots, indicating a daily correlation between the emissions of both gases. This correlation may be linked to seasonality in certain sites. Soil temperature emerged as a leading factor in shaping the daily patterns of N2O fluxes in most sites, exhibiting also a 24-hour pattern. Although the periodicities related to soil water content were less clear, a discernible pattern persisted with variations within sites. However, we will deepen into the discussion of these results and their implications in our EGU presentation.   Key words: N2O fluxes, hot-moments, soil environmental variables, temporal series, wavelet coherence analysis