You are here

Home

Harvard Forest >

Harvard Forest Symposium Abstract 2015

  • Title: Decadal trends for Pine and Oak Nitrogen Metabolism (Foliar and Sapwood) in Response to Chronic Nitrogen Amendments at the Harvard Forest, MA
  • Primary Author: Rakesh Minocha (USDA Forest Service)
  • Additional Authors: Stephanie Long (USDA Forest Service); William McDowell (University of New Hampshire - Main Campus); Subhash Minocha (University of New Hampshire); Swathi Turlapati (University of New Hampshire - Main Campus)
  • Abstract:

    We evaluated the long-term (1992 to 2008) trends in foliar and sapwood metabolism, soil solution chemistry, and tree mortality rates in response to chronic N additions to pine and hardwood stands at the Harvard Forest Long Term Ecological Research (LTER) site. Common stress-related metabolites like polyamines, free amino acids and inorganic elements were analyzed for control, low nitrogen (LN, 50 kg NH4NO3 ha-1 yr-1) and high nitrogen (HN, 150 kg NH4NO3 ha-1 yr-1) treatments. In the pine stands, partitioning of excess nitrogen into foliar polyamines and amino acids increased with both treatments until 2002 as compared to the control. In 2005 these effects declined for HN and by 2008 they could only be observed for amino acids in LN plot. Significant decline in foliar Ca and P for some years (mostly in the HN plot) accompanied metabolic changes in polyamines and amino acids but by 2008 no such changes were observed. Foliar data were generally supported by the sapwood data, which also showed an increase in Ca and Mg in the HN plot in 2008. In line with these observations, mortality data revealed a large number of dead trees in HN pine plots by 2002; the mortality rate started to decline by 2005. Oak trees in the hardwood plot did not exhibit any major changes in polyamines, amino acids, nutrients and mortality rate with LN treatment indicating that thus far this species was able to tolerate the yearly doses of LN in the form of NH4N03. However, HN trees suffered from physiological and nutritional stress along with increased mortality in 2008. In this case also, foliar data were supported by the sapwood data. Overall, both low and high nitrogen applications have resulted in greater physiological stress to the pines than the oaks. Since these metabolic data are in line with published reports on soil microbial community structure changes, soil carbon sequestration rates, and wood biomass production rates for both the sites for this site, it is reassuring to suggest that these could be suggested for long-term monitoring of health of forest trees.

  • Research Category: Large Experiments and Permanent Plot Studies
    Physiological Ecology, Population Dynamics, and Species Interactions

  • Figures:
    • Minocha et al.-Figs (1-7) .pdf