Effects of fertilization and three years of throughfall reduction on leaf physiology of loblolly pine

Climate models project decreased soil water availability in the southeastern United States, which may impact loblolly pine (Pinus taeda L.) productivity. In conjunction with an interdisciplinary project known as PINEMAP, the objective of this study was to investigate the interactive effects of fertilization and a 30 percent reduction in throughfall on physiological characteristics that affect forest productivity. Stand growth, leaf area index (LAI) and leaf physiology were monitored over three years of treatment. Only the most recent preliminary results are presented here for June 2014. The study is a factorial combination of throughfall reduction (30 percent versus ambient) and fertilization (fertilized versus non-fertilized) treatments in a now 9-year-old loblolly pine plantation located in Georgia. No interactive effects of treatment were significant for any variable. Fertilization increased basal area by 19 percent, basal area increment by 27 percent, and peak LAI by 29 percent. Throughfall reduction reduced peak LAI by 17 percent. Fertilization decreased stomatal conductance, likely in response to higher LAI and increased water use combined with low ambient precipitation. These results indicate fertilization can increase growth and LAI but increased LAI may lead to short-term leaf physiological sensitivity to drought.