Pasture soils in the Southern Brazilian Highlands as net atmospheric methane sinks along a management intensification gradient

Soils under pasture-based livestock systems can act as atmospheric methane (CH 4 ) sinks; however, their capacity to sustain net CH 4 uptake under contrasting management intensities remains poorly quantified. This study aimed to evaluate the impact of different grazing systems on soil CH 4 fluxes across an intensification gradient in the Southern Brazilian Highlands, including natural grassland (NG), improved natural grassland (ING), perennial pasture (PP), and annual pasture (AP). CH 4 fluxes were monitored over one year alongside water-filled pore space (WFPS) and mineral nitrogen concentrations (NH 4 + -N and NO 3 − -N). Linear mixed models (LMM) were used to evaluate the relationship between CH 4 fluxes and environmental variables across the four grazing systems. All systems acted predominantly as net CH 4 sinks, with stronger and more stable uptake in NG and ING, and reduced sink strength in PP and AP. Soil moisture emerged as the dominant control of CH 4 fluxes, with maximum uptake occurring under well-aerated conditions (<60% WFPS). As WFPS increased, CH 4 uptake declined and shifted toward net emissions under near-saturation conditions, reflecting oxygen limitation and transient methanogenic activity. Short-lived emission pulses were observed following urea application and post-drought rewetting events, particularly in PP and AP; however, these were associated with concurrent increases in soil moisture rather than with nitrogen availability per se, as mineral nitrogen forms showed no significant direct effects on CH 4 fluxes under the conditions evaluated. These findings demonstrate that CH 4 dynamics in pasture soils are primarily governed by soil moisture and aeration, with management intensity modulating the magnitude and stability of the sink. Overall, maintaining soil structural integrity and aeration is critical to sustaining CH 4 uptake, highlighting the role of well-managed subtropical pastures as active components of climate change mitigation.