Photosynthesis and Biomass Allocation in Oak Seedlings Grown Under Shade
Abstract-Northern red oak (Quercus rubra L.) (NRO) and white oak (Q. alba L.) (WO) acorns were sown into wooden plots and grown under 30 percent shade screen (30 percent S) or 70 percent shade screen (70 percent S). Seedlings grown under full sun were the controls (C). At the end of the first year, the 30 percent S NRO had 30 percent greater seedling dry weight (DW) than C seedlings. No growth differences existed between these two treatments after 2 years. Compared to C, 70 percent S NRO had a 40 percent lower net photosynthetic rate (A), twofold less seedling DW and leaf number, and fourfold less lateral root DW after 2 years. Dry weight biomass allocation to lateral roots increased from 17 percent at the end of the first growing season to 22 percent after 2 years for both the C and 30 percent S NRO. The 70 percent S seedlings, however, allocated only 8 percent DW to lateral roots for both years. White oak seedlings responded similarly to shade as NRO seedlings. The 70 percent S WO had 30 percent lower A and fourfold less lateral root DW than the controls after 2 years. At the end of the second year, DW biomass allocation to lateral roots was 12, 7, and 5 percent, respectively, for C, 30 percent S, and 70 percent S WO seedlings. The impact of shade (reduced light intensity) on seedling growth of both oak species was discussed in terms of A, photoprotection, and DW biomass allocation.