| dc.description.abstract | The effects of elevated atmospheric CO2 concentrations on plant polyphenolic concentration, tannin concentration and chemical composition were investigated in leaves of sub-tropical grass species and fynbos shrubs. The working hypothesis was based on predictions that carbon based secondary compounds (polyphenolics and tannins) would increase when carbon in excess of growth requirements accumulate in plant leaves under nutrient imbalanced conditions. This imbalance would arise due to an increase in atmospheric CO2 level.
Furthermore, empirical evidence suggests that nutrient paucity would enhance carbon-based secondary compound production. This hypothesis was tested in two different systems involving plants with differential photosynthetic mechanisms and growth strategies.
. Polyphenolics, tannins and chemical composition (N, P, C and TNC) were quantified in grass species from a natural, C+ dominated, sub-tropical grassland in KwaZulu/Natal. Three plots were subjected to different freeair CO2 enrichment treatments, i.e. elevated (550-800 ppm), intermediate (no more than 400 ppm) and ambient CO2 (currently at 365 ppm). One of the seven grass species, Alloteropsis semialafa, had Cs photosynthetic mechanism. o Polyphenolics, tannins and chemical composition (N, P, C and TNC) were quantified in three fynbos species grown in open-top chambers under controlled greenhouse conditions. The plants were grown under ambient (360 ppm) and ambient + 350 ppm CO2 in typical low nutrient acid sands of the fynbos biome. This study shows that despite some of the grasses having the capacity to
produce tannin-like substances, polyphenolics and tannins do not increase in the grass species studied. Polyphenolic and tannin concentrations were increased only in Leucadendron laureolum amongst the fynbos species. Its sister species Leucadendron xanthoconus did not show any change in phenolic or tannin concentrations. | en_US |
