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C 3 –C 4 composition and prior carbon dioxide treatment regulate the response of grassland carbon and water fluxes to carbon dioxide
Author(s) -
POLLEY H. W.,
DUGAS W. A.,
MIELNICK P. C.,
JOHNSON H. B.
Publication year - 2007
Publication title -
functional ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.272
H-Index - 154
eISSN - 1365-2435
pISSN - 0269-8463
DOI - 10.1111/j.1365-2435.2006.01213.x
Subject(s) - carbon dioxide , grassland , transpiration , photosynthesis , zoology , carbon dioxide in earth's atmosphere , ecosystem , flux (metallurgy) , biology , growing season , botany , agronomy , ecology , chemistry , organic chemistry
Summary1 Plants usually respond to carbon dioxide (CO 2 ) enrichment by increasing photosynthesis and reducing transpiration, but these initial responses to CO 2 may not be sustained. 2 During May, July and October 2000, we measured the effects of temporarily increasing or decreasing CO 2 concentration by 150–200 µmol mol −1 on daytime net ecosystem CO 2 exchange (NEE) and water flux (evapotranspiration, ET) of C 3 –C 4 grassland in central Texas, USA that had been exposed for three growing seasons to a CO 2 gradient from 200 to 560 µmol mol −1 . Grassland grown at subambient CO 2 (< 365 µmol mol −1 ) was exposed for 2 days to an elevated CO 2 gradient (> 365 µmol mol −1 ). Grassland grown at elevated CO 2 was exposed for 2 days to a subambient gradient. Our objective was to determine whether growth CO 2 affected the amount by which grassland NEE and ET responded to CO 2 switching (sensitivity to CO 2 ). 3 The NEE per unit of leaf area was greater (16–20%) and ET was smaller (9–20%), on average, at the higher CO 2 concentration during CO 2 switching in May and July. The amount by which NEE increased at the higher CO 2 level was smaller at elevated than subambient growth concentrations on both dates, but relationships between NEE response and growth CO 2 were weak. Conversely, the effect of temporary CO 2 change on ET did not depend on growth CO 2 . 4 The ratio of NEE at high CO 2 to NEE at low CO 2 during CO 2 change in July increased from 1·0 to 1·26 as the contribution of C 3 cover to total cover increased from 26% to 96%. Conversely, in May, temporary CO 2 enrichment reduced ET more in C 4 ‐ than C 3 ‐dominated grassland. 5 For this mesic grassland, sensitivity of NEE and ET to brief change in CO 2 depended as much on the C 3 –C 4 composition of vegetation as on physiological adjustments related to prior CO 2 exposure.