What was done
After four years exposure to treatment combinations of ambient (350 ppm) and elevated (650 ppm) atmospheric CO2 concentrations and ambient and elevated (ambient + 3°C) air temperatures, sugar maple (Acer saccharum) seedlings growing in open-top chambers located in Tennessee, USA, had various leaf optical properties and chlorophyll concentrations measured to determine if they were affected by elevated CO2 and temperature.

What was learned
Elevated CO2 and temperature, alone and in combination, did not significantly affect any of the leaf spectral properties measured, including reflectance, transmittance and absorbance.  Furthermore, they had no significant influence on leaf chlorophyll concentrations or the chlorophyll a/b ratio.  Nonetheless, it was noted that during an unusually hot summer two years into the experiment, leaves of seedlings growing in the elevated air temperature treatment were visibly chlorotic, while no such injury was noted in leaves of trees grown in the elevated CO2/elevated air temperature combination, suggesting that atmospheric CO2 enrichment was protecting leaf chlorophylls from high temperature degradation.

What it means
As the atmospheric CO2 concentration increases, it is likely that little change will occur in the spectral properties of sugar maple leaves, thereby allowing them to continue to absorb sufficient sunlight to support enhanced carbon fixation during the process of photosynthesis.  Moreover, it is unlikely that this phenomenon will be influenced by moderate increases in air temperature.  In fact, even if air temperatures became unseasonably high, it is likely that elevated levels of atmospheric CO2 would ameliorate any high temperature-induced stresses that might otherwise lead to the degradation of important photosynthetic pigments, including chlorophyll.