Drought reduced monoterpene emissions from the evergreen Mediterranean oak <i>Quercus ilex</i>: results from a throughfall displacement experiment

Abstract

Abstract. The effects of water limitations on the emission of biogenic volatile organic compounds are not well understood. Experimental approaches studying drought effects in natural conditions are still missing. To address this question, a throughfall displacement experiment was set up in a natural forest of Quercus ilex, an evergreen Mediterranean oak emitting monoterpenes. Mature trees were exposed in 2005 and 2006 either to an additional drought, to irrigation or to natural drought (untreated control). In both years, absolute monoterpene emission rates as well as the respective standard factors of the trees exposed to normal and additional drought strongly declined during the drought periods. Monoterpene emissions were lower in year 2006 than in year 2005 (factor 2) due to a more pronounced summer drought period in this respective year. We observed a significant difference between the irrigation and additional drought or control treatment: irrigated trees emitted 82% more monoterpenes during the drought period 2006 than the trees of the other treatments. However, no significant effect on monoterpene emission was observed between normal and additional drought treatments, despite a significant effect on leaf water potential and photochemical efficiency. During the development of drought, monoterpene emissions responded exponentially rather than linearly to decreasing leaf water potential. Emissions rapidly declined when the water potential dropped beCorrespondence to: A.-V. Lavoir (avlavoir@gmail.com) low −2 MPa and photosynthesis was persistently inhibited. Monoterpene synthase activities measured in vitro showed no clear reduction during the same period. From our results we conclude that drought significantly reduces monoterpene fluxes of Mediterranean Holm oak forest into the atmosphere due to a lack of primary substrates coming from photosynthetic processes.

A novel reflectance-based model for evaluating chlorophyll concentrations of fresh and water-stressed leaves

“…As leaves dehydrate or vegetation suffers water stress, leaf water potential becomes increasingly negative and the rate of photosynthesis is reduced (Nilsen and Orcutt, 1996;Montagu and Woo, 1999;Keenan et al, 2009;Lavoir et al, 2009) because water deficit can cause chlorophyll degradation and thus significantly decreases foliar chlorophyll concentration (Kirnak et al, 2001;Pirzad et al, 2011;Desotgiu et al, 2012;Ghorbanli et al, 2013). Specifically, the magnesium ion (Mg 2+ ) of the chlorophyll will be removed.…”

Process-based simulation of seasonality and drought stress in monoterpene emission models

“…Measurements of leaf scale emissions are taken from Grote et al (2009a) and Lavoir et al (2009) Enzyme activity has been determined in 2006 according to standard protocols described in Fischbach et al (2000) using the same leaves as used for emission measurements. Enzymatic data provide calibration information for the seasonal dynamics model SIM.…”

“…In order to compare the effect of the seasonality in the three model approaches, simulations are additionally run with a fixed emission factor of 28 µg gDW −1 h −1 (Seufert et al, 1997) which is in good accordance with the measured maximum factor at the site in Puéchabon reported by Lavoir et al (2009). The value has been transformed into enzyme activity using the reciprocal of Eq.…”

“…However, measurements for model evaluation at these times and places are scarce. It has also been demonstrated that the variation between years is considerable which underlines the importance of long-term investigations (Lavoir et al, 2009). Finally, for evaluating the upscaling procedure, stand scale emission measurements are urgently needed.…”

“…Bertin and Staudt, 1996;Brilli et al, 2007;Staudt et al, 2008). Strong, long-lasting drought, however, decreases isoprenoid emissions considerably (Hansen et al, 1999;Pegoraro et al, 2004, Lavoir et al, 2009. Overall, an impact of summer drought on annual isoprenoid emission has frequently been observed (Geron et al, 1997;Plaza et al, 2005).…”