Rodent-induced grassland degradation increases annual non-CO2 greenhouse gas fluxes and NO losses despite CH4 uptake enhancement

Widespread degradation of grasslands due to human activities and climate change provides favorable habitats for subterranean rodents, whose subsequent bioturbation such as burrowing and mound building further exacerbates the ongoing degradation, thereby directly and indirectly altering biogeochemical C and N cycles. However, it remains unclear how rodent-induced degradation of grasslands affects soil CH₄, N₂O and NO fluxes. Here we report two-year field measurements of these trace-gas fluxes and associated environmental controls from different degradation treatments (unaffected or moderately affected meadow, heavily affected meadow with very severe signs of degradation) across three alpine meadow sites at different elevations on the Tibetan Plateau. Our results show that seasonal patterns of these gas fluxes were driven by the variations in soil temperature, moisture and C or N availability, and that non-growing season fluxes contributed 29 %-39 %, 29 %-93 % and 16 %-61 % to the annual CH₄, N₂O and NO budgets, respectively. Over the multiple site-years, annual CH₄ uptake ranged from 1.14–1.49 kg C ha^-1 yr^-1 for the healthy meadows to 1.42–2.85 kg C ha^-1 yr^-1 for the degraded meadows, indicating significant increases in CH₄ uptake following grassland degradation by rodents. However, the climate benefits of increased CH₄ uptake were overshadowed by a significant stimulation of annual N₂O emissions following the degradation, resulting in the net non-CO₂ greenhouse gas (GHG) fluxes of 48.1–364 kg CO₂-eq ha^-1 yr^-1. Also, grassland degradation by rodents significantly increased annual NO emissions to 0.35–1.19 kg N ha^-1 yr^-1. Based on estimates of rodent-induced degradation across the Tibetan alpine grasslands, we estimated that degradation increased soil non-CO₂ GHG emissions by 2012 Gg CO₂-eq yr^-1 and stimulated NO losses by 9.54 Gg N yr^-1. Our results highlight the important contribution of rodent-induced grassland degradation to regional or global climate change, and point to the urgent need for policy development for the sustainable use of grasslands.