Drought effect on isoprene production and consumption in Biosphere 2 tropical rainforest

Abstract

Isoprene is the most abundant of the hydrocarbon compounds emitted from vegetation and plays a major role in tropospheric chemistry. Models predict that future climate change scenarios may lead to an increase in global isoprene emissions as a consequence of higher temperatures and extended drought periods. Tropical rainforests are responsible for more than 80% of global isoprene emissions, so it is important to obtain experimental data on isoprene production and consumption in these ecosystems under control of environmental variables. We explored isoprene emission and consumption in the tropical rainforest model ecosystem of Biosphere 2 laboratory during a mild water stress, and the relationship with light and temperature. Gross isoprene production (GIP) was not significantly affected by mild water stress in this experiment because the isoprene emitters were mainly distributed among the large, canopy layer trees with deep roots in the lower soil profile where water content decreased much less than the top 30 cm. However, as found in previous leaf level and whole canopy studies, the ecosystem gross primary production was reduced by (32%) during drought, and as a consequence the percentage of fixed C lost as isoprene tended to increase during drought, from ca. 1% in wet conditions to ca. 2% when soil water content reached its minimum. GIP correlated very well with both light and temperature. Notably, soil isoprene uptake decreased dramatically during the drought, leading to a large increase in daytime net isoprene fluxes.

Isoprene emission from terrestrial ecosystems in response to global change: minding the gap between models and observations

“…Past studies have revealed that I s is less sensitive to water stress than A, and that I s tends to remain stable, or is modestly enhanced during periods of acute water stress (e.g. Fang et al 1996;Bruggemann & Schnitzler 2002;Pegoraro et al 2005Pegoraro et al , 2006. In one comprehensive analysis, drought was shown to have resulted in a significant decrease in I s in a red oak forest in the northeastern United States (Funk et al 2005).…”

Leaf level emissions of volatile organic compounds (VOC) from some Amazonian and Mediterranean plants

“…Several screening projects of VOC emissions from tropical African (Harley et al, 2003), Asian (Klinger et al, 2002;Geron et al, 2006b;Oku et al, 2008;Llusia et al, 2013), or South American including Amazonia (Lerdau and Keller, 1997;Throop, 1999, 2000;Harley et al, 2004;Pegoraro et al, 2006) have been performed reporting on isoprene emissions. A few plant species were identified as monoterpene emitters, among them Hevea brasiliensis (Klinger et al, 2002;Baker et al 2005;Geron et al, 2006b;Wang et al, 2007).…”

“…isoprene (Lerdau and Keller, 1997;Throop, 1999, 2000;Harley et al, 2004;Pegoraro et al, 2006;Oku et al, 2008;Ferreira et al, 2010;Misztal et al, 2010). Because of the heterogeneity of ecoregions, species diversity, inaccessibility, and logistical and methodological difficulties, the number of investigations made in tropical regions is limited (Geron et al, 2002;Kesselmeier et al, 2002Kesselmeier et al, , 2009Kuhn et al, 2002aKuhn et al, , b, 2004Kuhn et al, , 2007Harley et al, 2004).…”

Simulating atmospheric composition over a South-East Asian tropical rainforest: performance of a chemistry box model

“…In another modelling study over tropical rainforest Ganzeveld et al (2008) calculate that about 90% of their modelled isoprene flux exits the rainforest canopy. The missing 10% is not all reacted, with soil uptake also playing a role (Cleveland and Yavitt, 1997;Pegoraro et al, 2006). Given that oxidation products themselves may be deposited before exiting the canopy, the above canopy-flux of oxidation products will be a relatively small proportion of the whole.…”