Sulfur biogeochemical dynamics of grassland soils in northern China transect along an aridity gradient

• Identifying two key aridity index (AI) thresholds that determine sulfur process dynamics along the NCT. • A notable shift from abiotic to biotic sulfur processes occurs at an AI of 0.12. • Sulfur cycling undergoes a transition from microbial to plant process dominance at an AI of 0.32. • Sulfate-reducing bacteria exhibit broader environmental adaptability, even thriving in arid and oxygen-rich conditions. As an essential nutrient element for biological growth and metabolism, sulfur is closely interlinked with the carbon and nitrogen cycles, and it is one of the limiting elements for grassland productivity. Here we investigated the spatial distribution of sulfur contents and 34 S stable isotope along the North China Transect (NCT), with the aim to explore the shaping role of the aridity index (AI) gradient on sulfur cycling dynamic in arid and semi-arid grasslands. In the area with AI < 0.12, soil sulfur contents and sulfur isotopic compositions (δ 34 S) showed no correlation with AI, indicating that abiotic processes predominantly govern the sulfur cycle in this area. In the area where 0.12 ≤ AI < 0.32, both sulfur contents and δ 34 S values increased with rising AI, with microbial-mediated reduction being the primary sulfur cycling process. In the area with 0.32 ≤ AI < 0.60, soil sulfur contents continued to increase with higher AI, but δ 34 S significantly decreased as AI increased, suggesting plant uptake as the dominant sulfur cycling process in this area. This study demonstrated the significant impact of AI on sulfur dynamics, providing insights into the different drivers of sulfur cycling along the aridity gradient, and offering guidance for developing targeted strategies under global climate change.