title: Elevated CO2increases belowground respiration in California grasslands.
abstract: This study was designed to identify potential effects of elevated CO2on belowground respiration (the sum of root and heterotrophic respiration) in field and microcosm ecosystems and on the annual carbon budget. We made three sets of respiration measurements in two CO2treatments, i.e., (1) monthly in the sandstone grassland and in microcosms from November 1993 to June 1994; (2) at the annual peak of live biomass (March and April) in the serpentine and sandstone grasslands in 1993 and 1994; and (3) at peak biomass in the microcosms with monocultures of seven species in 1993. To help understand ecosystem carbon cycling, we also made supplementary measurements of belowground respiration monthly in sandstone and serpentine grasslands located within 500 m of the CO2experiment site. The seasonal average respiration rate in the sandstone grassland was 2.12 μmol m-2s-1in elevated CO2, which was 42% higher than the 1.49 μmol m-2s-1measured in ambient CO2(P=0.007). Studies of seven individual species in the microcosms indicated that respiration was positively correlated with plant biomass and increased, on average, by 70% with CO2. Monthly measurements revealed a strong seasonality in belowground respiration, being low (0-0.5 μmol CO2m-2s-1in the two grasslands adjacent to the CO2site) in the summer dry season and high (2-4 μmol CO2m-2s-1in the sandstone grassland and 2-7 μmol CO2m-2s-1in the microcosms) during the growing season from the onset of fall rains in November to early spring in April and May. Estimated annual carbon effluxes from the soil were 323 and 440 g C m-2year-1for the sandstone grasslands in ambient and elevated CO2. That CO2-stimulated increase in annual soil carbon efflux is more than twice as big as the increase in aboveground net primary productivity (NPPa) and approximately 60% of NPPain this grassland in the current CO2environment. The results of this study suggest that below-ground respiration can dissipate most of the increase in photosynthesis stimulated by elevated CO2.
authors.affiliation: Department of Biological Sciences, Stanford University, 94305, Stanford, CA, USA. yluo@maxey.dri.edu.
authors.forename: Yiqi
authors.initials: Y
authors.lastname: Luo
authors.affiliation: Department of Biological Sciences, Stanford University, 94305, Stanford, CA, USA.
authors.forename: Robert B
authors.initials: RB
authors.lastname: Jackson
authors.affiliation: Department of Plant Biology, Carnegie Institution of Washington, 94305, Stanford, CA, USA.
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Field
authors.affiliation: Department of Biological Sciences, Stanford University, 94305, Stanford, CA, USA.
authors.forename: Harold A
authors.initials: HA
authors.lastname: Mooney
keywords: Carbon cycle; Ecosystem; Global change; Respiration