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Large Drought-Induced Variations in Oak Leaf Volatile Organic Compound Emissions during PINOT NOIR 2012
Citation:
Geron, Chris, R. Daly, P. Harley, R. Rasmussen, R. Seco, A. Guenther, T. Karl, AND L. Gu. Large Drought-Induced Variations in Oak Leaf Volatile Organic Compound Emissions during PINOT NOIR 2012. CHEMOSPHERE. Elsevier Science Ltd, New York, NY, 146:8-21, (2016).
Impact/Purpose:
The data presented here demonstrate that drought had a significant effect on IL and ML basal emission rates as well as temperature and light response. These effects should be incorporated into air quality modeling systems. Drought effects varied significantly between species, and it is important to note that such effects cannot be detected from whole-canopy flux studies. Even within an oak canopy classification, variation in species composition could result in significant differences in response to drought and high temperatures. For instance, a forest stand composed of Quercus stellata, Q. muehlenbergii, and Q. macrocarpa could produce dramatically different isoprene fluxes during dry, hot conditions compared to a forest dominated by Q. alba, Q. rubra, and Q. velutina. Taken together, however, the drought responses of the individual species at MOFLUX are generally consistent with canopy fluxes of isoprene given the Quercus species composition near the tower. The leaf level data are also consistent with laboratory effects of drought on IL documented in previous studies, suggesting a drought-induced breakdown of the dependence of IL on TL particularly within the Erythrobalanus subgenus of Quercus. Low levels of leaf monoterpene emissions measured before and during the drought of 2012 suggest that non-oak sources of these compounds may be controlling above canopy fluxes. Additional leaf-level studies are needed in the field for both IL and ML during drought-affected growing seasons. Screening of other species with thermal and drought stress tolerance similar to Q. stellata, which are adapted to the semi-arid eastern deciduous forest-prairie Great Plains interface, is also warranted. Quantitative soil to leaf water relationships and their impacts on BVOC emissions are needed to improve BVOC emission model performance under drought stress conditions.
Description:
Leaf-level isoprene and monoterpene emissions were collected and analyzed from five of the most abundant oak (Quercus) species in Central Missouri’s Ozarks Region in 2012 during PINOT NOIR (Particle Investigations at a Northern Ozarks Tower ‐ NOx, Oxidants, Isoprene Research). June measurements, prior to the onset of severe drought, showed isoprene emission rates and leaf temperature responses similar to those previously reported in the literature and used in Biogenic Volatile Organic Compound (BVOC) emission models. During the peak of the drought in August, isoprene emission rates were substantially reduced, and response to temperature was dramatically altered, especially for the species in the red oak subgenus (Erythrobalanus). Quercus stellata (in the white oak subgenus Leucobalanus), on the other hand, increased its isoprene emission rate during August, and showed no decline at high temperatures during June or August, consistent with its high tolerance to drought and adaptation to xeric sites at the prairie-deciduous forest interface. Mid-late October measurements were conducted after soil moisture recharge, but were affected by senescence and cooler temperatures. Isoprene emission rates were considerably lower from all species compared to June and August data. The large differences between the oaks in response to drought emphasizes the need to consider BVOC emissions at the species level instead of just the whole canopy. Monoterpene emissions from Quercus rubra in limited data were highest among the oaks studied, while monoterpene emissions from the other oak species were 80 to 95% lower and less than assumed in current BVOC emission models. Major monoterpenes from Q. rubra (and in ambient air) were p-cymene, α-pinene, β-pinene, d-limonene, γ-terpinene, β-ocimene (predominantly1,3,7-trans-β-ocimene, but also 1,3,6-trans-β-ocimene), tricyclene, α-terpinene, sabinene, terpinolene, and myrcene. Results are discussed in the context of canopy flux studies conducted at the site during PINOT NOIR, which are described elsewhere. The leaf isoprene emissions before and during the drought were consistent with above canopy fluxes, while leaf and branch monoterpene emissions were an order of magnitude lower than the observed above canopy fluxes, implying that other sources may be contributing substantially to monoterpene fluxes at this site. This strongly demonstrates the need for further simultaneous canopy and enclosure BVOC emission studies.
