Strong growing season soil methane uptake observed in a restored prairie-savanna

Humid tallgrass prairies in the Upper Midwest have been largely converted to agriculture, creating large regional sources of greenhouse gases through soil oxidation and nutrient enrichment. Although prairie restoration is expanding, greenhouse gas fluxes from restored ecosystems remain poorly quantified. We measured growing season soil carbon dioxide, methane, and nitrous oxide fluxes across restored oak woodland, open tallgrass prairie, and wet prairie at Nachusa Grasslands, Illinois, and tested how fluxes were controlled by soil temperature, moisture, cover type, and elevation, and associations with surface soil microbial communities. Across all cover types, soils were consistent carbon dioxide sources (median 2.29 μmol m-2 s-1), methane sinks (median −0.36 nmol m-2 s-1), and neutral for nitrous oxide. Woodland soils were exceptionally strong methane sinks, while open prairie was often near neutral. Notably, net methane emission was absent even in wet prairie. Decision tree models explained 50%–70% of variability in carbon dioxide and methane fluxes, with soil temperature as the dominant control on carbon dioxide and cover type plus soil moisture most important for methane uptake. Inferred microbial community composition was dominated by putative aerobic taxa, including decomposers, nitrogen cyclers, and methane oxidizers. These results indicate that restored Midwest prairie-savanna ecosystems likely function as net greenhouse gas sinks, with particularly high rates of methane uptake in woodlands. Future work should incorporate non-growing season fluxes and vegetation fluxes to develop full ecosystem greenhouse gas budgets and better quantify the climate mitigation potential of prairie restoration.