Seasonal shifts in isoprenoid emission compositions from three
hyperdominant tree species in central Amazonia
Abstract
Volatile isoprenoids regulate plant performance and atmospheric
processes, and Amazon forests comprise the dominant source to the global
atmosphere. Still, there is a poor understanding of how isoprenoid
emission capacities vary in response to ecophysiological and
environmental controls in Amazonian ecosystems. We measured isoprenoid
emission capacities of Amazonian hyperdominant tree species—Protium
hebetatum, Eschweilera grandiflora, Eschweilera coriacea — across
seasons and along a topographic and edaphic environmental gradient in
the central Amazon. From wet to dry season, both photosynthesis and
isoprene emission capacities strongly declined, while emissions
increased among the heavier isoprenoids—monoterpenes and
sesquiterpenes. Plasticity across habitats was most evident in P.
hebetatum, which emitted sesquiterpenes only in the dry season, at rates
that significantly increased along the hydro-topographic gradient from
white sands (shallow root water access) to upland (deep water table). We
suggest that emission composition shifts are part of a plastic response
to increasing abiotic stress (e.g., heat and drought) and reduced
photosynthetic supply of substrates for isoprenoid synthesis. Our
comprehensive measurements suggest that more emphasis should be placed
on other isoprenoids besides isoprene in the context of abiotic stress
responses. Shifting emission compositions have implications for
atmospheric responses due to the strong variation in reactivity among
isoprenoid compounds.