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Canopy gas exchange and growth of upland pasture swards in elevated CO 2
Author(s) -
WOLFENDEN J.,
DIGGLE P. J.
Publication year - 1995
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1995.tb01831.x
Subject(s) - grassland , photosynthesis , growing season , canopy , agronomy , pasture , productivity , biomass (ecology) , respiration , environmental science , nitrogen , zoology , chemistry , botany , biology , organic chemistry , economics , macroeconomics
summary Vegetation monoliths (450 × 450 mm) from two contrasting upland grassland communities were grown in Solardomes in either ambient air or ambient air enriched with 250 ppm CO 2 During the first two growing seasons measurements of canopy gas exchange showed that rates of photosynthesis of limestone swards were enhanced by growth in elevated CO 2 , by approx. 50% during spring and early summer. Although canopy respiration was also greater in elevated CO 2 the overall effect was an average increase of 33% in net CO 2 assimilation. Enhanced respiration rates persisted into the autumn, whereas the effect on photosynthesis diminished through the growing season, so that in September swards growing in high CO 2 had net photosynthesis rates similar to, or even lower than those in ambient air. This response varied between swards of differing species composition. In acidic grassland no significant effects of CO 2 on respiration or net CO 2 uptake rates were detected at any time. The above ground productivity of limestone grassland was measured in several harvests throughout both seasons, and was not affected by CO 2 concentration at any time. Similarly, the acidic grassland, harvested at the end of the second season, showed no significant effect of CO 2 on above‐ground biomass. The results suggest that increasing atmospheric CO 2 concentration is unlikely to cause large changes in net primary productivity in these grasslands.