Climate impact on biosphère atmosphere relationship : does water stress affect the seasonal cycle of biogenic volatile ?

Project coordinator

Elena ORMENO-LAFUENTE - elena.ormeno-lafuente (at)

 The EC2CO project entitled " Climate impact on biosphere-atmosphere relationship: does water stress affect the seasonal cycle of biogenic volatiles? “ was funded in 2012 by the national program Continental and coastal Ecosphere (EC2CO) within the theme of BIOHEFECT (biogeochemistry, hydrology and ecosystem functioning). Several research centers were involved: IMBE UMR 7263, LSCE-IPSL and OHP.

 This project features an interdisciplinary approach (atmospheric chemistry and chemical ecology) with a dual purpose. On the one hand, it aims at reducing the existing uncertainties about isoprene emission estimation using an in-situ monitoring of isoprene emissions released by Downy Oak over the seasonal course under water stress and natural raining conditions. Instant variations – within the order of a minute – of isoprene emissions are correctly described in the isoprene emission algorithms available to date (Guenther et al., 1995) while low frequency variations (days - weeks) related to changes in environmental conditions are still poorly represented. It has however been shown that these low-frequency variations significantly explain isoprene variations (Monson et al., 1994, Geron et al., 2000 Boissard et al., 2001, Petron and al., 2001). The lowest frequency considered for isoprene is the ambient air temperature over 10 days (Guenther et al., 2006). To reduce these uncertainties, we aim to create an isoprene emission algorithm using artificial neural networks, taking into account as much high (instantaneous) and low (seasonal water stress, circadian cycle) frequency variations as possible depending on environmental conditions. The results of this algorithm will be compared to those from the existing G95 algorithm (Guenther et al. 1995).

 On the other hand, the project seeks to understand whether t isoprene emission of Downy Oak responds to a physical mechanism given the extreme volatility of this volatile, or whether, by contrast, isoprene emission actually accounts for a protection mechanism against drought stress. To answer to this question we aim to answer to the following questions using an ecophysiological approach: as isoprene emission is artificially inhibited, how does Downy Oak physiology evolve? If these plants are then fed with exogenous inputs of isoprene, are their physiological performances improved?

branch chamber, isoprene emission

Fig 1: Two trees are studied at a time. At the top left of the picture, the control tree is studied (outside de rain exclusion plot). At the bottom right of the picture, the stress tree is studied (inside the rain exclusion plot). Each tree belongs to a different treatment. Three trees have been taken into account for each treatment. The dynamic enclosures are coupled to several instruments (GC-MS, PTR-MS, IRGA), and captors thereby allowing to understand the relationship between BVOC emissions and (i) plant physiology and, (ii) environmental factors of low and high frequency  variations (iii) their role in Downy Oak.

  A Downy Oak forest has been chosen as the terrestrial ecosystem model for these two goals because this species is a strong isoprene emitter with an emission rate of about 100 μg.g-1.h-1, against 10 and 1 μg.g-1.h-1 for moderately and weakly emitting species. From June to November 2012, the isoprene emission rate has been monitored every month on 6 Downy Oak trees: 3 from the control plot and 3 from the rain exclusion plot. Isoprene measurements were performed using a dynamic enclosure (see Figure 1). Isoprene measurements were accompanied by tree physiological measurements and environmental parameters inside and outside the enclosure (Figure 2).

temperature, isoprene emission

Fig 2: Preliminary relationship between isoprene emissions of white oak and ambient temperature.
DW: dry weight