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Net grassland carbon flux over a subambient to superambient CO 2 gradient
Author(s) -
Mielnick P. C.,
Dugas W. A.,
Johnson H. B.,
Polley H. W.,
Sanabria J.
Publication year - 2001
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1046/j.1354-1013.2001.00445.x
Subject(s) - flux (metallurgy) , growing season , ecosystem respiration , biomass (ecology) , zoology , grassland , daytime , photosynthesis , atmospheric sciences , environmental science , carbon flux , ecosystem , respiration , hydrology (agriculture) , horticulture , primary production , chemistry , botany , agronomy , ecology , biology , physics , geotechnical engineering , organic chemistry , engineering
Increasing atmospheric CO 2 concentrations may have a profound effect on the structure and function of plant communities. A previously grazed, central Texas grassland was exposed to a 200‐µmol mol −1 to 550 µmol mol −1 CO 2 gradient from March to mid‐December in 1998 and 1999 using two, 60‐m long, polyethylene‐ covered chambers built directly onto the site. One chamber was operated at subambient CO 2 concentrations (200–360 µmol mol −1 daytime) and the other was regulated at superambient concentrations (360–550 µmol mol −1 ). Continuous CO 2 gradients were maintained in each chamber by photosynthesis during the day and respiration at night. Net ecosystem CO 2 flux and end‐of‐year biomass were measured in each of 10, 5‐m long sections in each chamber. Net CO 2 fluxes were maximal in late May ( c. day 150) in 1998 and in late August in 1999 ( c. day 240). In both years, fluxes were near zero and similar in both chambers at the beginning and end of the growing season. Average daily CO 2 flux in 1998 was 13 g CO 2 m −2 day −1 in the subambient chamber and 20 g CO 2 m −2 day −1 in the superambient chamber; comparable averages were 15 and 26 g CO 2 m −2 day −1 in 1999. Flux was positively and linearly correlated with end‐of‐year above‐ground biomass but flux was not linearly correlated with CO 2 concentration; a finding likely to be explained by inherent differences in vegetation. Because C 3 plants were the dominant functional group, we adjusted average daily flux in each section by dividing the flux by the average percentage C 3 cover. Adjusted fluxes were better correlated with CO 2 concentration, although scatter remained. Our results indicate that after accounting for vegetation differences, CO 2 flux increased linearly with CO 2 concentration. This trend was more evident at subambient than superambient CO 2 concentrations.