Does vapor pressure deficit drive the seasonality of δ13C of the net land‐atmosphere CO2exchange across the United States?

• DOI: 10.1002/2017jg003795
• Publication Date: 2017-07-22T21:26:35Z
• Authors: B. Raczka; S. C. Biraud; J. R. Ehleringer; C.‐T. Lai; J. B. Miller; D. E. Pataki; S. R. Saleska; M. S. Torn; B. H. Vaughn; R. Wehr; D. R. Bowling
• Keywords: Seasonality; Mixing ratio; Stomatal Conductance

Abstract The seasonal pattern of the carbon isotope content (δ 13 C) atmospheric CO 2 depends on local and nonlocal land‐atmosphere exchange transport. Previous studies suggested that δ C net flux ( source ) varies seasonally as stomatal conductance plants responds to vapor pressure deficit air (VPD). We studied variation at seven sites across United States representing forests, grasslands, an urban center. Using a two‐part mixing model, we calculated for each site after removing background influence and, when possible, sources. Compared previous analyses, found reduced (March–September) in forest (0.5‰ variation). did not find consistent relationship between VPD (or other) sites, providing evidence response was cause global, coherent . In contrast grassland had larger (5‰) dominated by transitions 3 /C 4 grass productivity fossil fuel emissions, respectively. Our findings were sensitive location used account within model method determined Special consideration should be given depending whether intent is understand level dynamics or regional scale impacts exchange. amplitude varied land cover types driven changes deficit. largest amplitudes Mixing approaches may incorrectly calculate observations are remote and/or prone anthropogenic influence.