Highly Reactive Light-Dependent Amazonian Monoterpenes

Source: Jeff Chambers, Kolby Jardine, and Dan Hawkes

Despite their orders-of-magnitude differences in atmospheric reactivity and their great diversity in biological functioning, little is known about tropical monoterpenes—volatile organic compounds that are emitted by trees into the atmosphere and that may be involved in insect-plant and microbe-plant interactions, as well as playing anti-oxidant roles to assist photosynthesis during abiotic stresses at times of environmental extremes.

In a recently published study in Geophysical Research Letters, a group of climate scientists headed by ESD’s Kolby Jardine and Jeff Chambers, together with Brazilian collaborators Antonio Manzi, Niro Higuchi, and graduate student Angela Jardine, sought to identify and quantify monoterpenes in both ambient forest air and as emissions from leaves in relation to photosynthesis in the Amazon Forest. As a part of the DOE Terrestrial Ecosystem Science (TES) supported GoAmazon 2014/15 project, the team investigated monoterpene light-dependent leaf emissions from a variety of tropical trees at a central Amazon field site, by developing a new field-portable photosynthesis and monoterpene emission auto-sampling system. They determined their atmospheric concentrations within and above a primary rainforest canopy, using a new rapid vertical-profiling technique. They found light-dependent leaf emissions of highly reactive monoterpenes from a number of abundant tree species, with emissions representing up to 2% of photosynthesis. Moreover, for the first time, they observed the buildup of these highly reactive monoterpenes in the ambient air within the tropical forest canopy.

Their results suggest that the emissions of highly reactive monoterpenes from plants protect photosynthesis during stress by acting as powerful anti-oxidants. Similar oxidation chemistry occurs in the atmosphere through monoterpene atmospheric oxidation, which generates low volatility oxidation products that can serve as secondary organic aerosol precursors. Thus, their discovery of highly reactive monoterpenes at the ecosystem scale represent a new uncharacterized local source of secondary organic aerosols, which play critical roles in climate through their interactions with radiation and clouds. The team suggested that Amazon trees able to produce highly reactive monoterpenes may have an advantage over isoprene-producing trees in future climate and land-use change scenarios. The research is expected to stimulate a large number of studies in plant biochemistry and physiology, atmospheric chemistry and climate, and land-use change in the tropics.

Citation:

Jardine, A.B., K.J. Jardine, J.D. Fuentes, S.T. Martin, G. Martins, F. Durgante, V. Carneiro, N. Higuchi, A.O. Manzi, and J.Q. Chambers (2015), Highly reactive light-dependent monoterpenes in the Amazon.  Geophysical Research Letters, DOI: 10.1002/2014GL062573.

Funding: BER Terrestrial Ecosystem Science