Assessing Environmental Stress in Forests Using Cellular Markers

Minocha, Rakesh

USDA Forest Service Northeastern Research Station

Our focus is to identify metabolites or “cellular markers” that predict the impact of environmental pollution as well as biotic factors on health of forests by examining the foliage of visually asymptomatic trees. Our goal is to relate these markers to long term forest productivity. Environmental issues of concern include acidic deposition (especially N deposition) and heavy metals. Atmospheric deposition of nitrogen (N) may cause forest decline or enhance forest productivity depending on the initial N status of soils, and the rate and duration of N deposition. Heavy metals (Hg, Cd, Zn, Pb, and Cu) are toxic to plants and may decrease productivity when accumulated beyond threshold levels in soils. Our research has identified useful markers like putrescine (an aliphatic diamine), arginine (a common amino acid), and phytochelatins (metabolites produced by cells in response to heavy metal exposure) as cellular indicators. Foliar putrescine is a reliable and easily measurable marker of stress in visually healthy trees. It has also been shown to ameliorate some of the effects of soil Ca deficiency as its concentrations increase in response to decreasing soil Ca. Foliar putrescine was shown to be present in higher levels in hemlock trees that were resistant to hemlock wooly adelgid compared to the susceptible trees.  Free amino acids, especially arginine, also increase in response to chronic N input at several hardwood and conifer sites and can indicate too much N availability or N saturation.  In a study on the Harvard Forest Long Term Ecological Research (LTER) site, these changes were also accompanied by lower site productivity in red pine. In another project with red spruce, we observed that phytochelatins and their precursor accumulate in response to heavy metal exposure.

Land Session - Wednesday Afternoon

corresponding author:

Northeastern Research Station
P. O. Box 640
271 Mast Road
Durham, NH 03824 USA
603-868-7622
rminocha@fs.fed.us