ANALYSIS OF OZONE CONCENTRATION - BIOMASS RESPONSE RELATIONSHIPS AMONG OPEN-POLLINATED FAMILIES OF LOBLOLLY-PINE

Tropospheric ozone may contribute to the reported growth decline of pi nes in the southeastern United States. Ozone concentration - response relationships were quantified for open-pollinated families of loblolly pine (Pinus taeda L.) seedlings. Seedlings from 30 families were expo sed to ozone (0, 80, 160, 240, or 320 nL 03/L air) in greenhouse chamb ers for 6 h per day, 4 days per week, for 12 weeks. Top (shoot) and ro ot biomass were determined for each of 900 plants. Twelve families wer e selected for a subsequent experiment to examine consistency of resul ts (360 plants). For each response variable, statistical models consis ting of fixed and random effects were based on combined data for all f amilies and both experiments. Data were fit to both polynomial and Wei bull model types. The maximum suppression of any biomass variable (top , root, or total dry weight) predicted by a regression model for plant s exposed for 12 weeks to 320 nL/L was 25% for total dry weight (Weibu ll model based on data representing all 42 family-year combinations, t otal of 1260 plants). Families were ranked for sensitivity based on es timates of a single parameter from the models, and model type had no e ffect on the order of sensitivity rankings of the 42 family-experiment combinations. The same families represented die extremes in sensitivi ty among the 12 families that were exposed in both experiments.