The divergent role of straw return in soil O2 dynamics elucidates its confounding effect on soil N2O emission

The divergent effects of straw returns on nitrous oxide (N2O) 2 O) emissions from soil require elucidation of the underlying mechanisms and factors that explain the inconsistency in in-situ conditions. We conducted a field experiment based on a long-term trial under different regimes of nitrogen (N) fertilization and straw management, complemented by laboratory incubation experiments involving visualized O2 2 dynamics imaging. In the field trial, we performed hourly basis high-time-resolution measurements of soil matrix oxygen (O2), 2 ), N2O 2 O concentrations and fluxes during N2O 2 O "hot moment" events. We found that straw return increased cumulative N2O 2 O emissions by 32.7% under conventional high N input (Ncon), con ), but showed no effect on N2O 2 O emission under optimized N input (Nopt). opt ). In situ O2 2 content and further microcosm experiments with visualized O2 2 spatiotemporal distribution suggested that long-term straw return increases porosity and soil O2 2 content, which reduced N2O 2 O emission under low N substrate conditions by improving soil pore structure and aeration during "hot moment" events. By contrast, straw return increased N2O 2 O emission via creating short-term O2 2 depletion zone and triggering denitrification in anoxic microsites when excess N substrate was available. Although straw return showed inconsistent effects on N2O 2 O emission under different N application rates, it consistently decreased N2O 2 O concentration in the soil matrix during the "hot moment" events, suggesting that straw return increases the transport of the produced N2O 2 O in soil matrix to the soil surface. Our study underscores the multifaceted role of straw return in soil O2 2 dynamics, i.e., stimulating O2 2 consumption in a short-term microscale of soil, but increasing soil porosity in a long-term mesoscale of soil. This explains the confounding effects of straw management on the production and transportation of soil N2O 2 O in situ and emphasizes the importance of optimized N fertilization for reducing the "hot moment" N2O 2 O emissions when straw is incorporated.