The Influence of Nitrogen Deposition on Root Lifespan in Northeastern Temperate Forests

MS in Ecology, 2011

Collaborators: Dali Guo, Zhengquan Wang, Erica Smithwick, Lindsey Rustad, Richard Bowden, Gary Lovett, Charlie Driscoll

The effect of N deposition on fine root life span in five temperate forest stands at three sites, Bear Brook Watershed in Maine, Mt. Ascutney, and Harvard Forest, was investigated in Northeastern US. Whole-plot or watershed-level N fertilization (15.4 - 150 kg ha-1yr-1 N) at the three sites was started in 1988 or 1989. Minirhizotron images were collected monthly over the growing season from 2003 through 2004 to record and analyze for fine root dynamics. The effect of N fertilization on root lifespan, as well as the interaction of N with soil depth, root diameter, and birth season of roots, was investigated. Nitrogen addition severely decreased root lifespan in three softwood forests, while moderately increased root lifespan in two hardwood forests. However, not all root cohorts were equally affected by N addition. The hypothesis that surface roots, thinner roots, and summer born roots are most negatively affected by N addition, in terms of root lifespan, was only true for certain roots cohorts in certain forests. The inconsistency in the influence of N deposition on root lifespan reflects the complex nature of belowground demographic dynamics. Utilizing survival analysis tools enhanced the ability to quantify interactions, which serves as a first step towards better understanding the effects of N deposition on root lifespan in temperate forests. To explain the variation in root lifespan change under N addition, soil chemistry, root N concentration, and root oxidative stress were examined in a suite of long-term N addition experiments including the three northeastern sites. However, root oxidative stress could not explain the change of root lifespan under N addition.


Du, Quanying. 2011. The influence of nitrogen deposition on root lifespan in Northeastern temperate forests. M.S. Thesis. The Pennsylvania State University.