Variability of BVOC emissions from a Mediterranean mixed forest in southern France with a focus on <i>Quercus pubescens</i>

Abstract

Abstract. We aimed at quantifying biogenic volatile organic compound (BVOC) emissions in June from three Mediterranean species located at the O 3 HP site (southern France): Quercus pubescens, Acer monspessulanum and C. coggygria (for isoprene only). As Q. pubescens was shown to be the main BVOC emitter with isoprene representing ≈ 99 % of the carbon emitted as BVOC, we mainly focused on this species. C. coggygria was found to be a non-isoprene emitter (no other BVOCs were investigated).To fully understand both the canopy effect on Q. pubescens isoprene emissions and the inter-individual variability (tree to tree and within canopy), diurnal variations of isoprene were investigated from nine branches (seven branches located to the top of canopy at ≈ 4 m above ground level (a.g.l.), and two inside the canopy at ≈ 2 m a.g.l.).The Q. pubescens daily mean isoprene emission rate (ER d ) fluctuated between 23 and 98 µgC g −1 DM h −1 . Q. pubescens daily mean net assimilation (Pn) ranged between 5.4 and 13.8, and 2.8 and 6.4 µmol CO 2 m −2 s −1 for sunlit and shaded branches respectively. Both ER d and isoprene emission factors (Is), assessed according to Guenther et al. (1993) algorithm, varied by a factor of 4.3 among the sunlit branches. While sunlit branches ER d was clearly higher than for shaded branches, there was a non-significant variability of Is (59 to 77 µgC g −1 DM h −1 ). Diurnal variations of isoprene emission rates (ERs) for sunlit branches were also investigated. ERs were detected at dawn 2 h after Pn became positive and were mostly exponentially dependent on Pn. Diurnal variations of ERs were not equally well described throughout the day by temperature (C T ) and light (C L ) parameters according to G93 algorithm. Temperature had more impact than photosynthetically active radiation (PAR) on the morning emissions increase, and ER was no longer correlated to C L × C T between solar noon (maximum ER) and mid-afternoon, possibly due to thermal stress of the plant. A comparison between measured and calculated emissions using two isoprene algorithms (G93 and MEGAN -Model of Emissions of Gases and Aerosols from Nature) highlighted the importance of isoprene emission factor Is value used, and some weakness in assessing isoprene emissions under Mediterranean climate conditions (drought) with current isoprene models.

The Tree Drought Emission MONitor (Tree DEMON), an innovative system for assessing biogenic volatile organic compounds emission from plants

“…The reported technical solutions range from simple branch bags [35, 43] to environmentally controlled inert chambers [36, 44–48]. Most studies use either commercial leaf chamber systems [32, 49, 50] or self-build chambers [44], yet multiple parallel (N > 2) chamber designs are rarely presented [51, 52].…”

Mediterranean forests, land use and climate change: a social-ecological perspective

“…Holm oak at Puechabon (Limousin et al 2008(Limousin et al , 2009(Limousin et al , 2012, Aleppo pine at Font Blanche (Gea-Izquierdo et al 2015) and downy oak at O 3 HP (Santonja et al 2015b) are concerned. Results show that changing rainfall pattern will affect (1) directly litter production and decomposition, and (2) volatile organic compounds emissions (Staudt et al 2002(Staudt et al , 2003Genard et al 2015). The idea is to develop around the Mediterranean basin a network of experimental stations with simpler and less expensive devices to monitor the effects of climate change in other important forest ecosystems and so under other bioclimates.…”

Resistance of native oak to recurrent drought conditions simulating predicted climatic changes in the Mediterranean region

“…Two identical dynamic branch enclosures were used for sampling CO 2 and H 2 O exchange as well as isoprene emission (see below). The enclosures are fully described in Genard-Zielinski et al (2015), and only slight modifications were made as described in Saunier et al (2017).…”