Straw-mulching rather than plastic-mulching strengthens ammonia-oxidizing archaea in driving nitrification in a nitrogen-fertilized calcareous soil

Abstract

Ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) are essential in driving soil ammonia oxidation, thus regulating NO₃⁻ leaching losses in terrestrial ecosystems. However, the potential nitrification activity (PNA), AOA, and AOB, and their intrarelationships and potential drivers in concurrent mulching and N fertilization remain elusive. To address these issues, we collected soil samples from a field experiment treated with mulching (CT, no mulch; RF, plastic-mulched ridges and straw-mulched furrows; SM, straw mulch) and N fertilization (0, 120, and 240 kg N ha⁻¹) for 16-years. The results showed that PNA was ranked as SM > RF ≈ CT and significantly increased with increasing N. Mulching had a stronger influence than N rate on the abundance, Shannon index, and beta diversity of AOA and AOB, but the N rate had more significant impacts on the phylogeny of AOA and AOB. Microbial nutrient limitation, soil organic carbon, and available potassium (AK) were vital determinants regulating the abundance, Shannon index, and beta diversity of AOA, while these parameters were mediated by pH, total N, and NO₃⁻ for AOB. PNA was linearly dependent on AOA and AOB abundance, and significantly correlated with Nitrososphaera cluster 4 (AOA) and Nitrosospira clusters 2, 3b, and 11 (AOB). Partial least squares path modeling further illustrated that mulching significantly affected PNA through mediating AOA in CT–SM rather than CT–RF, although the AOB-induced contribution to PNA exceeded that of AOA, suggesting an essential role of straw-mulching retention in enhancing the AOA contribution to ammonia oxidization. The N rate had greater impacts than mulching on PNA, and pH and AK were the two most important edaphic variables influencing PNA through mediating AOA and AOB. Collectively, these results provide evidence that AOB dominates nitrification in concurrent mulching and N-fertilized calcareous soils and highlight the capacity of straw mulching to strengthen the contribution of AOA to PNA.