DOI: 10.5061/dryad.tb2rbp033
title: Leaf flammbility and volatiles of Ginkgo, Agathis, and Dicksonia

description: The Triassic-Jurassic Boundary marks the third largest mass extinction
 event in the Phanerozoic, characterised by a rise in CO2-concentrations
 from ~600 ppm to ~2100 – 2400ppm, coupled with a ~3.0 – 4.0°C temperature
 rise. This is hypothesized to have induced major floral turnover, altering
 vegetation structure, composition and leaf morphology, which in turn are
 hypothesized to have driven changes in wildfire. However, the effects of
 elevated CO2 on fuel properties, such as chemical composition of leaves,
 are also important in influencing fire behaviour, but yet have not been
 considered. We test this by selecting three Triassic analogue species
 grown experimentally in different atmospheric compositions, and analyse
 variations in leaf chemistry, and leaf level flammability. These data were
 used to inform a fire behaviour model. We find that all three species
 tested showed a reduction in their volatile component, leading to lower
 flammability. Accounting for these variations in a model, our results
 suggest that leaf intrinsic flammability has a measurable impact on
 modelled fire behaviour. If scaled up to ecosystem level, periods of
 elevated CO2 may therefore be capable of inducing both biochemical and
 morphological changes in fuel properties, and thus may be capable of
 influencing fire behaviour.
description: Plants (Ginkgo biloba, Agathis australis, and Dicksonia
 antarctica) were grown in ambient or high CO<sub>2</sub>
 growth chambers for 18 months, then new-growth leaves were selected for
 analysis. Intrinisic leaf flammbility data was
 collected using a Federal Aviation Administration Microcalorimeter (Fire
 Testing Technology, East Grinstead, UK), using 10-15 mg of dried leaf
 tissue for each sample and were exposed to a heating program that ramped
 up to 750°C at a rate of 3°C per second. Two leaves per plant from two
 plants were analysed each in duplicate. The peak heat release (pHRR: the
 most intense flux of heat during the combustion of the leaf material,
 indicates the maximum decomposition rate of the leaves which is related to
 the volatile gas flux of the material), heat capacity (HRC: the maximum
 capability of the leaf material to release combustion heat per degree of
 temperature during pyrolysis; this measure provides an indication of the
 resistance of the leaves to thermal degradation) and total heat release
 (THR: the total energy released by the leaf during combustion) was
 determined for each leaf on a g−1 dry mass basis.
 Lignin content was determined as follows: Protein-free cell wall
 preparations were obtained for 2 leaves per plant from 2 plants by
 sequential washing in pH 7 potassium phosphate buffer (0.1 M), 1 M NaCl
 solution, 1% (v/v) Triton-X100 and acetone. Acid-soluble lignin was
 assayed using the acetyl bromide method (Moreira-Vilar et al 2014), and
 the absorbance measured at 280 nm. Leaf volatile
 compounds were determined as follows: Volatiles were
 extracted from dried leaves (2 leaves per plant from 2 plants) ground in
 glass pestle and mortar under liquid nitrogen (0.01 g (dry weight) in 1 ml
 hexane with 10 µM butylated hydroxytoluene (BHT; as an internal standard)
 by sonication and subsequent overnight incubation. Samples were analysed
 using an Agilent 7200 series accurate mass Q-TOF mass spectrometer coupled
 to a 7890A GC system (Agilent Technologies, Santa Clara, USA), equipped
 with an EI (electron ionisation) ion source. 5 μl of each sample was
 injected into a non-deactivated, baffled glass liner with a 12:1 split
 ratio (14.448 ml min-1 split flow) and the inlet temperature was
 maintained at 250°C.   A Zebron semi-volatiles (Phenomenex, Torrance, USA)
 column (30 m x 250 μm x 0.25 μm) coupled with a 10 m guard column, was
 maintained at a constant helium flow of 1.2 ml min-1. The temperature of
 the column was ramped up at a rate of 15°C min-1, from 70°C to 310°C over
 16 min, and then held at 310°C for a further 6 minutes. The EI source
 emission current and voltage were held at 35 μA and 70 eV respectively. 
 The mass range was set from 50 to 600 m/z, with an acquisition rate of 5
 spectra s-1, and a solvent delay of 4 min. Data were analysed using
 Agilent MassHunter Qualitative Analysis software (version B.07.00) and
 compounds identified where possible by comparison with standards and NIST
 (NIST 11 Mass Spectral Library) and Golm libraries (Hummel et al,
 2007).