Isoprene emissions from plants are mediated by atmospheric CO₂ concentrations.

摘要

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 380ppmv 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.