Uncovering the Effects of Long‐Term Different Cropping Regimes on N ₂ O Emissions and Related Drivers in Black Soil

ABSTRACT Agricultural soils significantly contribute to global nitrous oxide (N 2 O) emissions. Different cropping regimes alter soil properties and microbial communities, influencing N 2 O emissions under nitrogen fertilization. However, the underlying mechanisms in black soil are unclear. We conducted a microcosm experiment using black soil subjected to 15 years of different cropping regimes: farmland fallow with no anthropogenic intervention (FALL), maize‐soybean rotation (MSR), continuous soybean (CSC), and continuous maize (CMC). Our results showed that N 2 O emissions were significantly higher in the FALL soil than in the other three cropping regimes, irrespective of exogenous N addition. This was mainly caused by the higher availability of C and N substrates, as well as the greater abundances of ammonia‐oxidizing archaea (AOA), ammonia‐oxidizing bacteria (AOB), and nir K genes. Furthermore, the elevated N 2 O emissions in FALL soils were also associated with shifts in microbial community composition and interaction. N 2 O emissions in FALL soils may also be linked to the enrichment of key bacterial taxa (e.g., Pseudonocardia ) within co‐occurrence networks associated with N 2 O production, and the decline in the relative abundance of key species (e.g., Gemmatimonas ) involved in N 2 O reduction. These findings highlighted that the N 2 O emissions from farmland fallow without human management represent a non‐negligible source of greenhouse gasses, particularly given the sustained microbial activity that persists even in the absence of crops and fertilizer inputs. Therefore, under scientific cropping systems and with proper nitrogen fertilizer application, the goal of reducing nitrous oxide emissions from black soil could be achieved.