Soil moisture determines nitrous oxide emission and uptake.

Soils are major sources and sinks of nitrous oxide (NO). The main pathway of NO emission is performed through soil denitrification; however, the uptake phenomenon in denitrification is overlooked, leading to an underestimation of NO production. Soil moisture strongly influences denitrification rates, but exact quantifications coupled with nosZ, nirK, and nirS gene analysis remain inadequately unaccounted for. In this study, a N-NO pool dilution (NOPD) method was used to measure NO production rates under different soil moisture levels. Therefore, 20%, 40%, 60%, 80% and 100% soil water holding capacity (WHC) were used. The results revealed that NO uptake rates increased proportionally with soil moisture content and peaked at 80% WHC with 4.17 ± 2.74 μg N kg soil h. The NO production and net emission rates similarly peaked at 80% WHC, reading at 32.50 ± 4.86 and 27.63 ± 3.09 μg N kg soil h during the incubation period (18 days). Soil moisture content increased the gene copy number of the nosZ, NH content, and denitrification potential in soil. NO uptake at WHC 80-100% was significantly greater than that at WHC 20-60%. It was attributed to a decrease in O and the high NO concentration inhibition (> 50 mg N kg of soil NO-N content). Principal components analysis (PCA) indicated that the number of nosZ genes was the major driver of NO uptake, especially nosZ clade II. Thus, the results of this study deepen our understanding of the mechanisms underpinning NO sources and sinks in soils and provide a useful gene-based indicator to estimate NO uptake.