Global-scale studies suggest that dryland ecosystems dominate an increasing trend in the magnitude and interannual variability of the land CO2 sink. However, such analyses are poorly constrained by measured CO2 exchange in drylands. Here we address this observation gap with eddy covariance data from 25 sites in the water-limited Southwest region of North America with… More

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It is necessary to partition eddy covariance measurements of carbon dioxide exchange into its offsetting gross fluxes, canopy photosynthesis, and ecosystem respiration, to understand the biophysical controls on the net fluxes. And independent estimates of canopy photosynthesis (G) and ecosystem respiration (R) are needed to validate and parametrize carbon cycle models that are coupled with… More

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This study examined the ability of the Photochemical Reflectance Index (PRI) to track seasonal variations in carotenoid pigments and photosynthetic activity of mature evergreen chaparral shrubs. Our results confirm that PRI scales with photosystem two (PSII) photochemical efficiency across species and seasons, as demonstrated by PRI’s strong correlation with de-epoxidized (photoprotective) xanthophyll cycle pigment levels… More

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This study reports the effects of long-term elevated atmospheric CO2 on root production and microbial activity, biomass, and diversity in a chaparral ecosystem in southern California. The free air CO2 enrichment (FACE) ring was located in a stand dominated by the woody shrub Adenostoma fasciculatum. Between 1995 and 2003, the FACE ring maintained an average… More

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Carbon flux in arid and semiarid area shrublands, especially in old-growth shrub ecosystems, has been rarely studied using eddy covariance techniques. In this study, eddy covariance measurements over a 100-year old-growth chamise-dominated chaparral shrub ecosystem were conducted for 7 years from 1996 to 2003. A carbon sink, from −96 to −155 g C m−2 yr−1, was determined under normal… More

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