TY - JOUR

T1 - Canopy gas exchange and growth of upland pasture swards in elevated CO2.

AU - Wolfenden, J.

AU - Diggle, Peter J.

PY - 1995

Y1 - 1995

N2 - 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 CO2 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 CO2, by approx. 50% during spring and early summer. Although canopy respiration was also greater in elevated CO2 the overall effect was an average increase of 33% in net CO2 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 CO2 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 CO2 on respiration or net CO2 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 CO2 concentration at any time. Similarly, the acidic grassland, harvested at the end of the second season, showed no significant effect of CO2 on above-ground biomass. The results suggest that increasing atmospheric CO2 concentration is unlikely to cause large changes in net primary productivity in these grasslands.

AB - 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 CO2 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 CO2, by approx. 50% during spring and early summer. Although canopy respiration was also greater in elevated CO2 the overall effect was an average increase of 33% in net CO2 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 CO2 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 CO2 on respiration or net CO2 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 CO2 concentration at any time. Similarly, the acidic grassland, harvested at the end of the second season, showed no significant effect of CO2 on above-ground biomass. The results suggest that increasing atmospheric CO2 concentration is unlikely to cause large changes in net primary productivity in these grasslands.

KW - Canopy photosynthesis • respiration • grasslands • elevated CO2 • productivity

U2 - 10.1111/j.1469-8137.1995.tb01831.x

DO - 10.1111/j.1469-8137.1995.tb01831.x

M3 - Journal article

VL - 130

SP - 369

EP - 380

JO - New Phytologist

JF - New Phytologist

SN - 1469-8137

IS - 3

ER -