![]() ![]() According to the most recent report released by the Inter-Governmental Panel on Climate Change (IPCC, 2013), global atmospheric CO 2 levels have increased from the pre-industrial level of 280 ppm to the present level of nearly 410 ppm and the growth rate of CO 2 concentration is projected to be accelerated with an unprecedented pace of ∼1.0 ppm/yr. It is widely evident that global atmospheric carbon dioxide (CO 2) concentration has dramatically increased since the nineteenth century industrial revolution, elevating by about 1.6 ppm/yr. The limiting effects of excessively high CO 2 concentrations may not only associate with changes in the biochemical and photochemical processes of photosynthesis, but also attribute to the declines in stomatal conductance and nitrogen availability. By contrast, the weaker CO 2 fertilization effect on the growth of perennial ryegrass and Kentucky bluegrass was sustained for a longer period due to their higher optimal CO 2 concentrations than tall fescue. The optimal CO 2 concentration for the growth of tall fescue was lower than those of perennial ryegrass and Kentucky bluegrass, and thus the CO 2 fertilization effect on tall fescue disappeared earlier than the other two species. Initial increases in atmospheric CO 2 concentration substantially enhanced the plant biomass of the three perennial grasses through the CO 2 fertilization effect, but this CO 2 fertilization effect was dramatically compromised with further rising atmospheric CO 2 concentration beyond the optimum. All three perennial grasses featured an apparent optimal CO 2 concentration for growth. ![]()
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