Effects of elevated atmospheric CO2 and temperature on leaf optical properties in Acer saccharum

Elevated partial pressures of atmospheric carbon dioxide, similar to numero us causes of plant stress, may alter leaf pigmentation and structure and th us would be expected to alter leaf optical properties. Hypotheses that elev ated CO2 pressure and air temperature would alter leaf optical properties w ere tested for sugar maple (Acer saccharum) in the middle of its fourth gro wing season under treatment. The saplings had been growing since 1994 in op en-top chambers and partial shade at Oak Ridge, Tennessee under the followi ng treatments: (1) ambient CO2 pressure and air temperature (control); (2) CO2 pressure approximately 30 Pa above ambient; (3) air temperatures 3 degr ees C above ambient; and (4) elevated CO2 and air temperature. Under elevat ed CO2 or temperature, spectral reflectance, transmittance and absorptance in the visible spectrum (400-720 nm) tended to change in patterns that gene rally are associated with chlorosis, with maximum differences from the cont rol near 700 nm. However, these changes were not significant at P = 0.05. A lthough reflectance, transmittance and absorptance at 700 nm correlated str ongly with leaf chlorophyll concentration, variability in chlorophyll conce ntration was greater within than among treatments. The lack of treatment ef fects on pigmentation explained the non-significant change in optical prope rties in the visible spectrum. Optical properties in the near-infrared (721 -850 nm) were similarly unresponsive to treatment with the exception of an increased absorptance throughout the 739-850 nm range in leaves that develo ped under elevated air temperature alone. This response might have resulted from effects of air temperature on leaf internal structure. (C) 2000 Elsev ier Science B.V. All rights reserved.