Bryophytes and Lichens in the Amazonian rainforest, a significant new source and sink of BVOCs.

Abstract:

Tropical rainforests are globally the largest source of reactive isoprenoids to the atmosphere. Such compounds impact gas phase oxidant levels and particle concentrations and so are important to both atmospheric chemistry and physics. Currently, the forest canopy is considered the dominant source of these emissions. But not only the trees themselves need to be considered as emitters, but also epiphytic organisms covering major parts of the stems, branches and even the leaves of tropical trees. Here we report about bryophytes and lichens being a previously unconsidered source of isoprenoids. In the current study we collected samples of bryophyte and lichen species at a pristine Amazon rainforest field site (Amazon Tall Tower Observatory) and placed them in a cuvette flushed with ambient rainforest air. An empty cuvette was used as a control. VOC fluxes were measured by PTR-MS by alternately measuring the mixing ratios of the control and sample cuvette. Measurements were replicated several times and spanned different seasons (wet/dry) and years (2016-2018). A liverwort genus (Symbiezidium Trevis.) that commonly occurs in the Amazonian rainforest was found to emit large quantities of sesquiterpenes, rivalling those from canopy emissions when the local spatial coverage is taken into account. A similarly common lichen genus (Lepraria Ach.), on the other hand, was found to emit only minor quantities of monoterpenes and sesquiterpenes, but showed an uptake of oxidation products of isoprene. Therefore, we conclude bryophytes and lichens are likely potent, yet understudied contributors to the atmospheric chemistry of VOCs in tropical forests.