Isoprene emissions from plants are mediated by atmospheric CO₂ concentrations

• Published in: Global change biology Vol. 17; no. 4; pp. 1595 - 1610
• Main Authors: POSSELL, MALCOLM, HEWITT, C. NICHOLAS
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.04.2011; Wiley-Blackwell
• Subjects: Acacia; Acacia nigrescens; algorithms; Animal and plant ecology; Animal, plant and microbial ecology; Atmospheric chemistry; Biological and medical sciences; biomass; Carbon dioxide; elevated CO2; Emission measurements; emission modeling; Emissions; Fundamental and applied biological sciences. Psychology; General aspects; General aspects. Techniques; Growth chambers; Isoprene; leaf area; Leaves; Methods and techniques (sampling, tagging, trapping, modelling...); Plant biology; Plant species; subambient CO2; Trees; isoprene; Carbon dioxide; Emission; Increase; Woody plant; emission modeling; Modeling; Acacia nigrescens; Concentration measurement; atmospheric chemistry elevated CO; Medium enrichment; Leguminosae; Dicotyledones; Atmosphere; Angiospermae; Acacia; Spermatophyta; subambient CO
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/j.1365-2486.2010.02306.x

The tropical African tree species Acacia nigrescens Oliv. was grown in environmentally controlled growth chambers at three CO₂ concentrations representative of the Last Glacial Maximum (∼180 ppmv), the present day (∼380 ppmv), and likely mid-21st century (∼600 ppmv) CO₂ concentrations. Isoprene (C₅H₈) emissions, per unit leaf area, were greater at lower-than-current CO₂ levels and lower at higher-than-current CO₂ levels relative to controls grown at 380 ppmv CO₂. Changes in substrate availability and isoprene synthase (IspS) activity were identified as the mechanisms behind the observed leaf-level emission response. In contrast, canopy-scale emissions remained unaltered between the treatments as changes in leaf-level emissions were offset by changes in biomass and leaf area. Substrate concentration and IspS activity-CO₂ responses were used in a biochemical model, coupled to existing isoprene emission algorithms, to model isoprene emissions from A. nigrescens grown for over 2 years at three different CO₂ concentrations. The addition of the biochemical model allowed for the use of emission factors measured under present day CO₂ concentrations across all three CO₂ treatments. When isoprene emissions were measured from A. nigrescens in response to instantaneous changes in CO₂ concentration, the biochemical model satisfactorily represented the observed response. Therefore, the effect of changes in atmospheric CO₂ concentration on isoprene emission at any timescale can be modelled and predicted.