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A winning proposal for the Innovative Research Program, 2009:
Soil Emissions of Volatile Organic Compounds in Response to Pine Beetle Attacks
Investigators: Russ Monson (Ecosystems Division), Joost deGouw (Environmental Chemistry Division) and Noah Fierer (Ecosystems Division)
Objectives:
We aim to study the types and origins of volatile organic compound (VOC) emissions from a subalpine forest in Colorado that is in the incipient stages of a pine beetle attack. We hypothesize that the death of lodgepole pine trees and deposition of their needles to the soil will shift the source of VOC emissions from live to decomposing foliage with concomitant production of novel VOCs. We propose to conduct a three-month measurement campaign at the Niwot Ridge AmeriFlux site during the summer of 2009, focusing on the analytical characterization of VOC emissions from the soil on plots with pine trees that have been girdled (simulating a pine beetle attack) at different times in the past seven years. We will also collect data on the VOC composition of air collected at different heights from the Niwot Ridge flux tower at weekly intervals to provide a high resolution picture of VOC production in a forest not yet subject to intense pine beetle attack. From these observations we will evaluate the potential for the current beetle epidemic that has devastated many forests in the Western U.S. and Canada to alter local-to-regional atmospheric chemistry and air quality. The research will permit us develop a full proposal to be submitted to an appropriate program for federal funding, and it will catalyze the collaboration among three active research groups in CIRES with interdisciplinary representation in two research divisions.
Background and Importance
The Western U.S. and Canada have been devastated by a pine beetle epidemic that has destroyed 9 million hectares of forest in Canada and 600,000 hectares of forest in Colorado. Recently, all lodgepole pine forests in Colorado have been rated as among the most susceptible to catastrophic beetle damage in the Western U.S. and state foresters in Colorado have estimated that all lodgepole pine stands in the Colorado Rockies will be dead within 3-5 years (New York Times, November 18, 2008). Past studies of atmospheric chemistry dynamics above the montane forests near Niwot Ridge, Colorado have shown that air from the Denver metropolitan corridor is progressively processed as it moves upslope, almost daily, during summer mountain-valley flow episodes (Fehsenfeld et al. 1983, Parrish et al. 1986, 1990). This processing often results in near-surface O3 concentrations at the Niwot Ridge site (at 3050 m elevation) that are higher than in Boulder (Fehsenfeld et al. 1983). During its upslope ascent, air containing nitrogen oxides (NOx) has the opportunity to mix with air containing forest-emitted VOCs, causing the photochemical production of O3 and aerosol. Thus, forest VOC emissions may contribute to this unique air quality problem, and the recent trend toward increased beetle attacks may change the types and amounts of VOCs emitted from the forest. The decomposition of needles and trees following a beetle attack is likely to be slow, occurring over several years. We aim to take advantage of a unique opportunity to study forest plots that were treated with simulated beetle kill, beginning seven years ago. We propose to use these plots to gain information on how beetle attacks are likely to affect soil VOC emissions. Within this context, we propose to test the following specific hypothesis: Does the beetle-induced death of lodgepole pine trees cause the soil beneath them to emit different types of VOCs and in different amounts over a seven-year response period?
What Makes this Innovative?
Most past studies of VOC emissions from landscapes have focused on the role of vegetation; few have focused on soils. Our preliminary studies conducted in the laboratory suggest that VOC emissions from soils could be significant in their quantity and atmospheric reactivity, particularly when those soils receive needle and root litter inputs. Furthermore, the pine beetle devastation of Western U.S. forests caught most people 'off guard'. The extent of the devastation was not anticipated and we did not have time to establish observation sites and platforms that could effectively track the environmental impacts caused by the epidemic. The availability of the forest plots we propose to use provides a unique opportunity to examine the likely influence of beetle outbreaks on atmospheric chemistry – a nexus that has not been explored in the field of surface-atmosphere interactions.
Expected Outcome and Impact
We expect the decomposition of needles and roots to accelerate the production of unique VOC compounds emitted from the soil. We expect the soil emissions to not be reflected in the VOC types and quantities present in natural canopy air at this site. In other words, if the cause of these unique soil emissions is from beetle-killed trees, then they should be rare in the air sampled from this forest, which is only in the initial stages of beetle attack.
Research Plan
We have a unique opportunity to take advantage of forest plots that were inadvertently treated for simulated beetle kill over the past seven years, and thus provide us with a time-series from which we can evaluate our central hypothesis. In 2002, 2003, 2004 and 2008 graduate students in Monson's lab set up replicated 10 x 10 m plots, each containing 2-3 lodgepole pine trees, and either girdled all the trees in the plot or left them ungirdled (for controls). Our aim in setting up this original experiment was to explore the role of tree sugar transport (from needles to roots) on the rate of CO2 loss from soil respiration. Serendipitously, this type of girdling treatment, with its associated uncoupling of roots from needles, imposes the same stress that kills beetle-attacked trees. Thus, we now have a time series of plots with girdled pine trees (and appropriate untreated controls) ranging back seven years. On the oldest plots (2002, 2003), the trees are clearly dead (death typically occurs 2-3 years after girdling) and their needles and roots have been decomposing in the soil for several years; on the youngest plots (2008), the trees should just begin to show signs of needle death this summer, though our measurements of soil respiration indicate that root and associated mycorrhizal fungus death was already beginning last summer. In all, we have 6 different girdled plots and 6 different control (ungirdled) plots for each year.
We propose to make measurements of soil VOC emissions from all plots and from different heights on the flux tower during the summer of 2009. We will use a stainless steel soil chamber coupled to a proton transfer reaction mass spectrometer (PTR-MS) to conduct the soil emissions measurements. Teflon tubing with an intervening flow meter allows air to be pushed through the chamber at a known flow rate. A pressure outlet maintains the chamber air at near ambient pressure. The outlet line from the chamber is sampled with the PTR-MS to provide near-real time estimates of all major VOCs. In order to make observations of natural forest air, we will connect the PTR-MS to the existing vertical profiling system (6 inlets) on the Niwot Ridge AmeriFlux tower and obtain a complete diurnal pattern of VOC concentrations at all inlet heights. We estimate that we can sample four plots per day. We also estimate that we can sample 12 plots at a time without moving the PTR-MS among plots. We will work three days per week to sample 12 plots. The fourth day of the week, we will run sample lines from the tower inlets to the PTR-MS to make the vertical profile observations. The fifth day of the week we will move the PTR-MS to a new set of plots in preparation for the next week's measurements. With this design we estimate that we can sample all 48 plots plus four days of vertical profile measurements per month. Thus, we can return to the plots three times during the three-month summer campaign.
Personnel
Five scientists will work on the project. Russ Monson and Noah Fierer will work with graduate student Chris Gray and post-doc Dolores Asensio (visiting from Spain) to conduct soil emissions sampling from the plots. Russ Monson will work with Dolores Asensio to conduct vertical profile measurements. Joost deGouw will work with all participants to set up the analytical analyses on the PTR-MS, including calibration procedures and to follow-up our identification of unknown VOCs using coupled gas-chromatography mass spectrometry.
References
1Fehsenfeld, F.C., Bollinger, M.J., Liu, S.C., Parrish, D.D., et al. (1983) A study of ozone in the Colorado mountains. J. Atmos. Chem. 1: 87-105.
2Parrish, D.D., Fahey, D.W., Williams, E.J., Liu, S.C., et al. (1986) Background ozone and anthropogenic ozone enhancement at Niwot Ridge, Colorado. J. Atmos. Chem. 4: 63-80.
3Parrish, D.D., Hahn, C.H., Fahey, D.W., Williams, E.J., et al. (1990) Systematic variations in the concentration of NOx (NO plus NO2) at Niwot Ridge, Colorado. J. Geophys. Res. 95: 1817-1836.
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216 UCB