Maize root and shoot litter quality controls short-term $ and $ 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 $ emissions, studies on root litter effects are scarce. This study aimed (1) to evaluate how fresh maize root litter affects $ emissions compared to fresh maize shoot litter, (2) to assess whether $ 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 $ 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 $ and $ 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 16S rRNA gene sequencing. Maize litter quality controlled ^−_3$ and WEOC availability and decomposition-related $ emissions. Emissions induced by maize root litter remained low, while high bioavailability of maize shoot litter strongly increased $ and $ emissions when both root and shoot litter were added. We identified a strong positive correlation between cumulative $ and $ 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 ^−_3$ and WEOC concentration resulting in much higher $ emissions, when both ^−_3$ and WEOC were available. A significant correlation was observed between total $ and $ emissions, the soil bacterial community composition, and the litter level, showing a clear separation of root + shoot samples of all remaining samples. Bacterial diversity 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 $ and $ emissions from crop residues, especially when soil mineral N is limited.