PARENT SESSION
Oral Session # 24: Photosynthesis and Respiration.
Presiding: A Leakey
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 203.

Interactive effects of UV radiation and N availability on the growth of Quercus rubra seedlings.

Manish, Chintamani^*,1, Peterjohn, William¹, ¹ West Virginia University, Morgantown, West Virginia

ABSTRACT- A 4 month, 3-way factorial experiment was conducted in a greenhouse to test whether the sensitivity of Quercus rubra seedlings to UV-B radiation was affected by N availability and/or the level of UV irradiation. Seedlings were exposed to 4 levels of UV radiation (UV-A or UV-A+B) in a split plot design. The 4 levels of irradiation represented a predicted UV-B_BE dose for 2010 (7.02 KJ/m²/day), current levels 6.31 KJ/m²/day), and 2 sub-ambient levels (5.70 KJ/m²/day, and 0.63 KJ/m²/day). Plants were grown in sand and watered daily with equal amounts of nutrient solutions. The N concentrations of the nutrient solutions varied (400, 1600, and 4000 M) to provide three levels of N addition. UV-B stimulated total biomass production only at the highest level of N addition (p=0.038), and this response is attributable primarily to a stimulation of root biomass (p=0.016). Growth of above-ground tissues was not affected by UV-B. However, the effect of UV dose, regardless of type (UV-A or UV-A+B), on stem growth depended on N availability. Plant height (p=0.013) and stem mass (p=0.042) decreased with increasing irradiance levels but only for plants receiving the highest level of N addition. This overall irradiance effect on stem growth may be attributable to increased levels of UV-A since it is a component of both light treatments. The production of UV-B absorbing compounds in leaves was consistently stimulated by UV-B (p<0.001) but we found a trend towards greater production at the lowest level of N addition (p=0.087). Since the sensitivity of red oak seedlings to UV-B (primarily root growth) and the level of UV-A (stem growth) were apparent only at the highest level of N availability, this suggests that the response of seedlings to altered light conditions in a regenerating forest may be significantly altered by changes in N availability.

Key words: UV-B, Nitrogen, Ultraviolet radiation, Quercus rubra