Microbial enzyme-driven carbon-nitrogen cycling processes of greenhouse gases in sandy sediments of river-oasis systems in arid regions

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Arid inland rivers are important components of the land–water–ocean continuum, yet the linkages among sediment texture, microbial-mediated processes, and greenhouse gas (GHG) production remain poorly understood in sandy systems. Here, we investigated surface (0–5 cm) and subsurface (5–10 cm) sediments from the Niya River Basin, a desert–oasis agricultural river in northwestern China, by integrating sediment particle-size characterization, physicochemical measurements, extracellular enzyme assays, GHG production experiments, and multivariate analyses. We examined how sediment texture and carbon–nitrogen substrate availability regulate enzyme activities and CO₂, CH₄, and N₂O production potentials. Sediments were dominated by sand (>78%) but exhibited pronounced spatial heterogeneity in enzyme activities and GHG production. Localized hotspots of enzyme activities and CH₄/N₂O production were associated with enriched TOC, TN, and NH₄ + . Multivariate analyses revealed depth-dependent environmental associations: surface processes were primarily linked to TOC and pH, whereas very coarse sand showed increased relative importance in subsurface sediments, particularly for GHG production. These findings demonstrate that sandy sediments in arid inland rivers are not inert environments; rather, carbon–nitrogen substrate availability and particle-size heterogeneity jointly shape microbial enzyme-mediated transformation processes and spatially variable GHG production potentials.