Effects of acute ozone exposure and methyl jasmonate treatment on white pine monoterpene and sesquiterpene emission rates

Biogenic volatile organic compounds (BVOCs) are produced by plants and include monoterpenes, sesquiterpenes, and their oxygenated derivatives. These BVOCs are one of the principal factors influencing the oxidative capacity of the atmosphere in forested regions, and impact both ozone concentration and secondary organic aerosol formation. Under normal conditions, the release of BVOCs to the atmosphere is primarily controlled by the vapor pressure of the relevant compounds within the plant tissue, which is in turn dependent on temperature as well as complex biochemical production processes. However, various natural and anthropogenic stressors can alter both the quantity and composition of the BVOCs emitted by plants. The impacts of most stressors on BVOC emissions have not been well characterized, particularly in a field setting. This study investigated the effects of two stressors on monoterpene and sesquiterpene emission rates at a field study site in northern Michigan: acute ozone exposure and treatment with methyl jasmonate, an herbivory proxy. The study included six repetitions of the same experiment, each time using a new set of sub-canopy White Pine specimens. For each experiment, dynamic branch enclosures were simultaneously used on three specimens: one ozone treatment tree, one methyl jasmonate treatment tree, and one control tree. The ozone treatment was performed by dosing the branch with 200 ppb ozone for two hours, and the methyl jasmonate treatment was performed by placing a cotton tip with approximately 200 µL of dilute methyl jasmonate solution into the enclosure for 24 hours. Similarly, cotton tips with just ethanol were placed into control enclosures for 24 hours. Sampling lines were placed in each enclosure and VOCs were collected onto cartridges packed with Tenax GR adsorbent. Samples were collected several times per day for at least two days before treatment and for five days after treatment. Cartridges were then transported back to WSU's Pullman campus, where they were analyzed via thermodesorption with an Agilent GC/MS/FID. This analysis allows the identification and quantification of several monoterpenes and sesquiterpenes in the samples. Preliminary results indicate that methyl jasmonate may initiate the expression of inducible terpenes not normally expressed under unstressed conditions. Further analysis of results is ongoing. Ultimately, the results of this study will enable improved estimates of the changes in BVOC emissions from white pine forests resulting from the predicted increases in tropospheric ozone and plant herbivory expected to accompany climate change.