SEASONAL PATTERNS OF BIOMASS ACCUMULATION AND CARBON ALLOCATION IN PINUS-TAEDA SEEDLINGS EXPOSED TO OZONE, ACIDIC PRECIPITATION, AND REDUCED SOIL MG

Seasonal patterns of biomass accumulation and carbon allocation were determined for 1-year-old loblolly pine (Pinus taeda L.) seedlings grown in soil having either 15 or 35-mu-g Mg.g-1 and exposed to subambient, ambient, or twice ambient levels of ozone (O3) and simulated rainfall at pH 3.8 or 5.2 in open-top chambers. Seedlings were harvested during the 1988 dormancy period, immediately prior to bud break in 1989, during the first and third foliar growth flushes of 1989, and at the end of the 1989 growing season. At each harvest, biomass of individual seedling components was determined for all seedlings, and C-14 allocation among components was determined on a subset of seedlings. Seedlings exposed to twice ambient O3 exhibited a delay in fine-root production at the beginning of the 1989 growing season and reduced coarse-root biomass at the end of the 1989 growing season. Acidic precipitation and soil Mg treatments did not significantly affect biomass at any harvest date, nor were any treatment interactions observed. Biomass accumulation and carbon allocation were strongly affected by plant phenological stage, with maximum root allocation immediately prior to bud break and maximum shoot allocation at the end of the growing season. Seedlings exposed to twice ambient levels of O3 exhibited increased total respirational losses, decreased foliar retention, and slightly reduced export of initial C-14 label to stem and roots compared with seedlings exposed to subambient O3; however, these trends were not statistically significant.