Abstract:

To investigate the effects of continuous cultivation on soil nitrification in desert oasis farmland， this study was conducted in typical oasis fields of the Hexi Corridor， including an uncultivated sandy land （USL）， a young oasis field （YOF， 24 years） and a old oasis field （OOF， 54 years of cultivation）. Soil physicochemical properties， inorganic nitrogen dynamics， potential nitrification rate （PNR）， net nitrification rate （NNR）， potential ammonia oxidation （PAO）， N₂O emission rates， and the abundance of ammonia-oxidizing bacteria （AOB） and archaea （AOA） were systematically analyzed. The relative contributions of AOA and AOB to PAO and N₂O emissions were assessed using selective inhibitor assays. Results showed that continuous cultivation decreased bulk density and sand content， shifted soil texture from sandy to loamy， and significantly increased NH{}_{\mathrm{4}}^{+}-N， NO{}_{\mathrm{3}}^{-}-N， total nitrogen， soil organic matter， and dissolved organic carbon. Prolonged cultivation enhanced inorganic nitrogen mineralization and nitrification， with OOF showing the highest NH{}_{\mathrm{4}}^{+}-N and NO{}_{\mathrm{3}}^{-}-N concentrations and emission rates （P<0.05）. Both PNR and NNR increased significantly with cultivation duration， with OOF being 7.4- and 3.9-fold higher than USL， respectively. PAO also increased with cultivation， with AOA-driven PAO contributing more than AOB. N₂O emission rates were highest in OOF and dominated by AOB. qPCR analysis indicated that continuous cultivation significantly increased the abundance of both AOA and AOB （P=0.001）， with AOA gene copy numbers being 1-2 orders of magnitude higher than AOB. Partial least squares path modeling （PLS-PM） revealed that the abundance of nitrification functional genes had the strongest positive effect on PNR （0.575）， followed by PAO （0.274）， while soil physical properties exerted a negative effect （-0.516）. Overall， continuous cultivation significantly enhanced the soil nitrification potential by improving soil structure， increasing nitrogen accumulation， and stimulating ammonia-oxidizing microbial activity.

Key words: oasis farmland, potential ammonia oxidation, potential nitrification rate, N₂O emissions, inorganic nitrogen