Changes in Physiological Functioning in Loblolly Pine Trees Undergoing Bark Beetle Simulated Mortality

摘要

The southeastern United States contains extensive loblolly pine (Pinus taeda L.) plantations at risk from bark beetle damage that can change ecosystem biogeochemical cycling. Functional changes in tree physiology have the potential to occur before visual evidence of mortality making them difficult to incorporate into ecosystem models. Therefore, we girdled loblolly pines to simulate bark beetle damage and measured physiological processes including sapflow rates, photosynthesis, litterfall, and needle nitrogen concentrations to determine the physiological changes occurring in trees undergoing mortality. We found that the girdling treatment took 5 months to significantly reduce sapflow rates but visual crown mortality occurred more than one year after girdling. Girdled pines had approximately 2.5 times lower water use than control pines and exhibited greater susceptibility to atmospheric water stress. Girdled and control pines had similar needle nitrogen concentrations and photosynthetic rates measured during the mortality year. However, more litterfall with higher nitrogen concentrations occurred in the mortality year than in the previous year, resulting in redistribution of carbon and nitrogen in the ecosystem. Overall, these data allow for better quantification of the effects of background disturbance levels and individual tree mortality on water, carbon, and nitrogen cycling within a loblolly pine ecosystem.