Methane and Nitrous Oxide Fluxes From Urban Soils to the Atmosphere

Land‐use change is an important driver of soil–atmosphere gas exchange, but current greenhouse‐gas budgets lack data from urban lands. Field comparisons of urban and non‐urban ecosystems are required to predict the consequences of global urban‐land expansion for greenhouse‐gas budgets. In a rapidly urbanizing region of the U.S. Great Plains, we measured soil–atmosphere exchange of methane (CH 4 ) and nitrous oxide (N 2 O) for one year in replicated ( n = 3) urban lawn, native shortgrass steppe, dryland wheat– fallow, and flood‐irrigated corn ecosystems. All soils were net sinks for atmospheric CH 4 , but uptake by urban, corn, and wheat–fallow soils was half that of native grasslands (−0.30 ± 0.04 g C·m −2 ·yr −1 mean ± 1 se ). Urban (0.24 ± 0.03 g N·m −2 ·yr −1 ) and corn (0.20 ± 0.02 g N·m −2 ·yr −1 ) soils emitted 10 times more N 2 O to the atmosphere than native grassland and wheat‐fallow soils. Using remotely sensed land‐cover data we calculated an upper bound for the contribution of lawns to regional soil–atmosphere gas fluxes. Urban lawns occupied 6.4% of a 1578‐km 2 study region, but contribute up to 5% and 30% of the regional soil CH 4 consumption and N 2 O emission, respectively, from land‐use types that we sampled. Lawns that cover small portions of the landscape may contribute significantly to regional soil–atmosphere gas exchange.