Maize root and shoot litter quality controls short-term CO₂ and N₂O emissions and bacterial community structure of arable soil

Chemical composition of root and shoot litter controls decomposition and, subsequently, C availability for biological nitrogen transformation processes in soils. While aboveground plant residues have been proven to increase N₂O emissions, studies on root litter effects are scarce. This study aimed (1) to evaluate how fresh maize root litter affects N₂O emissions compared to fresh maize shoot litter, (2) to assess whether N₂O emissions are related to the interaction of C and N mineralization from soil and litter, and (3) to analyze changes in soil microbial community structures related to litter input and N₂O emissions. To obtain root and shoot litter, maize plants (Zea mays L.) were cultivated with two N fertilizer levels in a greenhouse and harvested. A two-factorial 22 d laboratory incubation experiment was set up with soil from both N levels (N1, N2) and three litter addition treatments (control, root,root+shoot). We measured CO₂ and N₂O fluxes, analyzed soil mineral N and water-extractable organic C (WEOC) concentrations, and determined quality parameters of maize litter. Bacterial community structures were analyzed using 16SrRNA gene sequencing. Maize litter quality controlled NO⁻₃ and WEOC availability and decomposition-related CO₂ emissions. Emissions induced by maize root litter remained low, while high bioavailability of maize shoot litter strongly increased CO_<2 and N₂O emissions when both root and shoot litter were added. We identified a strong positive correlation between cumulative CO₂ and N₂O emissions, supporting our hypothesis that litter quality affects denitrification by creating plant-litter-associated anaerobic microsites. The interdependency of C and N availability was validated by analyses of regression. Moreover, there was a strong positive interaction between soil NO⁻₃ and WEOC concentration resulting in much higher N₂O emissions, when both NO⁻₃ and WEOC were available. A significant correlation was observed between total CO₂ and N₂O emissions, the soil bacterial community composition, and the litter level, showing a clear separation of root+shoot samples of all remaining samples. Bacterial di-versity decreased with higher N level and higher input of easily available C. Altogether, changes in bacterial community structure reflected degradability of maize litter with easily degradable C from maize shoot litter favoring fast-growing C-cycling and N-reducing bacteria of the phyla Actinobacteria, Chloroflexi, Firmicutes, and Proteobacteria. In conclusion, litter quality is a major driver of N₂O and CO₂ emis-sions from crop residues, especially when soil mineral N is limited.