Monoterpene emission and monoterpene synthase activities in the Mediterranean evergreen oak Quercus ilex L. grown at elevated CO₂ concentrations

Abstract

Monoterpene emissions, monoterpene synthase activities, photosynthesis, fluorescence yield in the dark and drought stress indicators (stomatal conductance and mid‐day water potential) were concurrently measured under similar temperature and illumination in current‐year leaves of Quercus ilex L. of plants grown in open‐top chambers at ambient (350 ppm) and elevated (700 ppm) CO2. The study was undertaken to understand the effect of CO2 on monoterpene biosynthesis, and to predict and parameterize the biogenic emissions at growing CO2 concentrations. The results of the 1998 and 1999 studies show that at elevated CO2, and in the absence of persistent environmental stresses, photosynthesis was stimulated with respect to ambient CO2, but that the emission of the three most abundantly emitted monoterpenes (α‐pinene, sabinene and β‐pinene) was inhibited by approximately 68%. The enzyme activities of the monoterpene synthases catalysing the formation of the three monoterpenes were also inhibited at elevated CO2 and an excellent relationship was found between monoterpene emission and activity of the corresponding enzyme both at ambient and elevated CO2. Interestingly, however, limonene emission was enhanced in conditions of elevated CO2 as it was also the corresponding synthase. The ratio between enzyme activity and emission of the three main monoterpenes was high (above 20) at ambient CO2 but it was below 10 at elevated CO2 and, for limonene, on both treatments. Our results indicate that the overall emission of monoterpenes at elevated CO2 will be inhibited because of a concurrent, strong down‐regulation of monoterpene synthase activities. When the enzyme activity does not change, as for limonene, the high photosynthetic carbon availability at elevated CO2 conditions may even stimulate emission. The results of the 1997 study show that severe and persistent drought, as commonly occurs in the Mediterranean, may inhibit both photosynthesis and monoterpene (α‐pinene) emission, particularly at ambient CO2. Thus, emission is probably limited by photosynthetic carbon availability; the effect of elevated CO2per se is not apparent if drought, and perhaps other environmental stresses, are also present.

Seasonal variations in terpene emission factors of dominant species in four ecosystems in NE Spain

“…The higher terpene emission rates in summer than in spring were also explained mostly by a large change in emission factor (capacity). Q. ilex is a strong emitter of terpenes, especially in warm summer conditions (Staudt and Seufert, 1995;Kesselmeier et al, 1996;Street et al, 1997;Holzinger et al, 2000;Llusia and Peñuelas, 2000;Loreto et al, 2001;Owen et al, 2001;Staudt et al, 2002;Plaza et al, 2005;Llusia et al, 2011). The Q. ilex monoterpene emission rates were 6.4 (3.7 for standardised values) times higher in summer than in spring, similar to reports of Llusia et al (2011) in a atypically warm and dry summer.…”

Process-based modelling of biogenic monoterpene emissions combining production and release from storage

“…It would seem that algorithms that include solely a response to increasing temperature would be more sensitive under future warming scenarios compared to those that also include a light-limitation, but the overall effects of climate change on other important processes like changes in leaf area index or vegetation cover would also need to be considered. What is more, it is uncertain whether the response of monoterpene production to increasing atmospheric CO 2 concentration follows a similar inhibitory pattern as is shown for isoprene in an increasing number of plants (Constable et al, 1999;Loreto et al, 2001;Staudt et al, 2001;Baraldi et al, 2004), although the similarity in the chloroplastic pathways would suggest a similar response.…”

The use of branch enclosures to assess direct and indirect effects of elevated CO2 on photosynthesis, respiration and isoprene emission of Populus alba leaves

“…Isoprene is formed predominantly from photosynthetic carbon fixation (Sharkey & Yeh 2001) and it was expected that the two processes be simultaneously stimulated by increasing availability of CO2. However, exposure to or growth at elevated CO2 often reduce isoprenoid emission by vegetation (Loreto & Sharkey 1990, Loreto et al 2001a, Scholefield et al 2004, Rosen stiel et al 2003, with few exceptions (e.g., Sharkey et al 1991, Rapparini et al 2001. This uncoupling between the two processes may be due to an inhibition of isoprene syn thase activity under elevated CO2 (Schole field et al 2004) or to a reduction of the availability of isoprene synthase substrate (predominantly dimethylallyl diphosphate (DMADP), Rosenstiel et al 2003).…”

“…Unlike photosynthesis, phytogenic iso prenoid emissions are relatively insensitive to, or are even negatively affected by elevat ed CO2 (Sharkey & Yeh 2001, Loreto et al 2001a. Sharkey et al (1991) found that the basal emission in Populus tremuloides seedlings grown in growth chambers was re duced by 30-40% in response to elevated CO2 (900 ppm).…”