Continuous Measurements Of Net CO2 Exchange By Vegetation And Soils In A Suburban Landscape

In a suburban neighborhood of Minneapolis–Saint Paul, Minnesota, USA, we simultaneously measured net CO₂ exchange of trees using sap flow and leaf gas exchange measurements, net CO₂exchange of a turfgrass lawn using eddy covariance from a portable tower, and total surface-atmosphere CO₂ fluxes (F_C) using an eddy covariance system on a tall tower. Two years of continuous measurements showed that net CO₂exchange varied among vegetation types, with the largest growing-season (Apr–Nov) net CO₂ uptake on a per cover area basis from evergreen needleleaf trees (−603 g C m⁻²), followed by deciduous broadleaf trees (−216 g C m⁻²), irrigated turfgrass (−211 g C m⁻²), and non-irrigated turfgrass (−115 g C m⁻²). Vegetation types showed seasonal patterns of CO₂exchange similar to those observed in natural ecosystems. Scaled-up net CO₂ exchange from vegetation and soils (F_C(VegSoil)) agreed closely with landscape F_Cmeasurements from the tall tower at times when fossil fuel emissions were at a minimum. Although F_C(VegSoil) did not offset fossil fuel emissions on an annual basis, the temporal pattern of F_C(VegSoil) did significantly alter the seasonality of F_C. Total growing season F_C(VegSoil)in recreational land-use areas averaged −165 g C m⁻² and was dominated by turfgrass CO₂ exchange (representing 77% of the total), whereas F_C(VegSoil) in residential areas averaged −124 g C m⁻² and was dominated by trees (representing 78% of the total). Our results suggest urban vegetation types can capture much of the variability required to predict seasonal patterns and differences in F_C(VegSoil) that could result from changes in land use or vegetation composition in temperate cities.