Grazing-induced manure input promoted the aerobic biodegradation of upland peat organic carbon in Zoige

Peatland degradation caused by grazing activities in Zoige gains increasing concern. This study investigated the impact of grazing-induced manure input on peat organic carbon (OC) degradation. Over 100 soil samples were collected from wetland, grassland, and forest (representing 94 % of the landscape in Zoige region). Microcosm incubation experiments were conducted with cattle manure application to soils. Emissions of CO₂ and CH₄ were analyzed, composition of OC were investigated using ¹³C solid-state nuclear magnetic resonance (¹³C NMR) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS), and bacterial community were studied using 16S rRNA. Manure addition significantly (p < 0.05) enhanced total gas fluxes in grassland (1.06 to 1.67-2.45 × 10¹² t C/(m²·yr)) and forest (1.38 to 2.44-3.00 × 10¹² t C/(m²·yr)) with a major contribution by CO₂ (95.7 %-99.9 %), and the higher manure addition showed stronger effect. Little influence was observed in wetland. Manure addition promoted the abundances of degraders of phenolics (Sphingomonas, Xanthomonas, and Stenotrophomonas) and complex carbohydrates (Luteitalea and Chitinophaga). Moreover, manure addition changed the composition of upland OC by reducing aromaticity fa (phenolic-C % and aromatic-C %) and increasing nominal oxidation state of carbon (NOSC). The results suggested that grassland and forest are sensitive to manure input compared to wetland. Specific efforts should be taken to protect grassland and forest from OC loss in grazing activities.