Research Projects

Project at a Glance

Project Status: complete

Title: Historical-scale biochemical markers of oxidant injury & exposure in pines.

Principal Investigator / Author(s): Higashi,richard M.

Contractor: UC Davis

Contract Number: 97-309


Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Ecosystem Impacts, Impacts


Abstract:

Due to the precursor sources and transport dynamics of California, photochemical oxidant injury to forests has been of concern for over 40-years (Miller et al., 1997). Ozone acts first at the biochemical level, so that biochemical markers in foliage have utility in controlled studies, but in the field, injury is best assessed by visible foliar damage (i.e., chlorotic mottle). Unfortunately, leaves are usually lost within five years, so field assessments of ozone injury must be updated periodically. This limits injury assessment to the duration of the study and to a small number of assessment sites. On the other hand, if there were permanent, biochemical markers of ozone injury, then both restrictions could be removed. A permanent marker would ultimately mean that long-term forest injury records could be established, freeing resources to assess a larger number of sites. Such a marker, that is also biochemical in nature means that links to the mechanism(s) of injury and hence links to the photochemical oxidant species most injurious to trees, might be established under field conditions.

Analysis of wood chemical structures from annual tree rings (i.e., dendrobiochemistry; cf. Fan and Higashi, 1999), has the potential to fill this need. In a 1994-96 seed project funded by the University of California, Davis (UCD), Center for Ecological Health Research, in cooperation with Michael Arbaugh and Paul Miller of the U.S. Department of Agriculture, Forest Service in Riverside, California. We chemically analyzed tree ring segments from ponderosa pines in the San Bernardino National Forest (NF). The technique we used is an advanced wood biochemistry tool known as pyrolysis-gas chromatography / mass spectrometry (pyro-GC/MS) (Faix et al., 1987). Since this method does not require pre-choosing the analytes, it is not limited by our current knowledge (or ignorance). Briefly stated, our pyro-GC/MS survey found two markers that correlate strongly to trees growing in ozone-injury sites northeast of the Los Angeles Basin in the post-World War II period. The two markers were the ratio of H-type to G-type lignins, and moieties of phytoalexins (a class of plant defense chemicals) bound to the wood matrix. It is reasonable to conjecture that more markers will be found in these extremely information-rich datasets.

Therefore, the objective of this project was to more definitively correlate tree ring biochemical markers with ozone injury indices at established ozone impacted sites. We set out to “map,” by pyro-GC/MS analysis of tree rings, a matrix of established ozone-impact and control stands of ponderosa pines in two studies: first in the San Bernardino NF and secondly at multiple sites in the Sierra Nevada. Initial efforts focused on the newly found H:G lignin ratio and phytoalexin markers. Parallel analyses were conducted on the lignin, phytoalexin, and antioxidant biochemistry of the needles to probe possible mechanisms of injury that may result in the wood marker response.


 

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