Carbon dioxide dynamics in a residential lawn of a tropical city.

Turfgrass is an important component of the urban landscape frequently considered as an alternative land cover to offset anthropogenic CO emissions. However, quantitative information of the potential to directly remove CO from the atmosphere by turfgrass systems is lacking, especially in the tropics. Most assessments have considered the carbon accumulated by grass shoots and soil, but not the release of CO to the atmosphere by soil respiration (i.e., soil CO efflux). Here, we measured at high-temporal resolution (30-min) soil CO efflux, production, and storage rate for nearly three years in a residential lawn of Singapore. Furthermore, we quantified the carbon capture related to biomass production and CO emissions from fossil fuel consumption associated with maintenance activities (e.g., mowing equipment). Warm and humid conditions resulted in relatively constant rates of soil CO efflux, CO storage in soil, and aboveground biomass production (3370, 652, 1671 Mg CO km yr; respectively), while the systematic use of mowing machinery emitted 27 Mg CO km yr. Soil CO efflux and CO mowing emissions represent carbon losses to the atmosphere, while CO storage in soil and biomass productivity represent gains of carbon into the ecosystem. Under a steady state in which soil CO losses are only compensated by atmospheric CO uptake by photosynthesis, an ideal clipping waste disposal management, in which no CO molecule returns to the atmosphere (i.e., clippings are not burnt), and a 3-week mowing regime, this site can act as a sink of 2296 Mg CO km yr. In the scenario of incinerating all clippings, the lawn acts as an emission source of 1046 Mg CO km yr. Thus, management practices that reduce mowing frequency together with clipping disposal practices that minimize greenhouse gas emissions are needed to make urban lawns a potential natural solution to mitigate global environmental change.