Analysis of ozone concentration–biomass response relationships among open-pollinated families of loblolly pine

Abstract

Tropospheric ozone may contribute to the reported growth decline of pines in the southeastern United States. Ozone concentration–response relationships were quantified for open-pollinated families of loblolly pine (Pinustaeda L.) seedlings. Seedlings from 30 families were exposed to ozone (0, 80, 160, 240, or 320 nL O3/L air) in greenhouse chambers for 6 h per day, 4 days per week, for 12 weeks. Top (shoot) and root biomass were determined for each of 900 plants. Twelve families were selected for a subsequent experiment to examine consistency of results (360 plants). For each response variable, statistical models consisting of fixed and random effects were based on combined data for all families and both experiments. Data were fit to both polynomial and Weibull model types. The maximum suppression of any biomass variable (top, root, or total dry weight) predicted by a regression model for plants exposed for 12 weeks to 320 nL/L was 25% for total dry weight (Weibull model based on data representing all 42 family–year combinations, total of 1260 plants). Families were ranked for sensitivity based on estimates of a single parameter from the models, and model type had no effect on the order of sensitivity rankings of the 42 family–experiment combinations. The same families represented the extremes in sensitivity among the 12 families that were exposed in both experiments.