Long-term dynamics of monoterpene synthase activities, monoterpene storage pools and emissions in boreal Scots pine

Abstract

Abstract. Seasonal variations in monoterpene emissions from Scots pine (Pinus sylvestris) are well documented, and emissions are often shown to follow the incident temperatures due to effects on compound volatility. Recent studies have indicated a link between monoterpene emissions and physiological drivers such as photosynthetic capacity during needle 15 development. The complex interplay between the dynamic changes in the biosynthetic capacity to produce monoterpenes and the temperature-dependent evaporation process of volatiles from internal storage reservoirs has not yet been studied under field conditions. Here, we analysed the relationships between needle monoterpene synthase activities, endogenous monoterpene storage pools and monoterpene emissions of needles in two consecutive years at a boreal forest site in Finland. 20The results showed changes in the monoterpene synthase activity of needles, linked to seasonality and needle ontogenesis, while the pool of stored monoterpenes (about 0.5% of dry weight) did not change considerably as a function of needle aging.Monoterpene emissions did not correlate directly with enzyme activity or the storage pool size. We observed notably high plant-to-plant variation in the biosynthesis rates of individual monoterpenes, which did not reflect the storage compound mixture. The enzyme activity producing δ-3-carene was only present in the first months after needle flushing, and decreased 25 with needle age, whereas δ-3-carene was abundant in the endogenous monoterpene pool and dominated the needle emissions.This study emphasizes the seasonal, developmental and intraspecific variability of monoterpene biosynthesis and storage, and calls for more in-depth analyses to reveal how such complex interaction affects monoterpene emissions from pine needles in boreal forests. 30Biogeosciences Discuss., https://doi

Effects of elevated growth temperature and enhanced atmospheric vapour pressure deficit on needle and root terpenoid contents of two Douglas fir provenances

“…Although the main compounds abundant in needles were released from both provenances, the composition of emitted terpenoids differed from the composition of needle-stored terpenoids. This finding is in good agreement with many studies on other species (Schindler and Kotzias, 1989;Peñuelas and Llusià, 1997;Llusià and Peñuelas, 1998;Geron et al, 2000;Ormeno et al, 2007;Vanhatalo et al, 2018;Yáñez-Serrano et al, 2018) despite also a close correlation between needle terpenoid content and terpenoid emission rates has been described in Douglas fir (Lerdau et al, 1995). The discrepancy between needle terpenoid levels compared to the emitted terpenoids might arise from different volatilities of the compounds, more than on storing structure within the needles (with different resistances for the volatiles), or a contribution of de novo synthesized compounds which has been demonstrated in several conifers (Ghirardo et al, 2010a).…”

“…The trends for the other compounds formed in the enzyme assays were less clear which might at least partially be due to either very low enzyme activities (for formation of isopulegol, β-citronellol, β-pinene) or low abundances of these terpenoids in needles of the PO provenance (nerolidol, geraniol). Similar inconsistencies between TPS activities and terpenoid levels in needles and leaves were found in Pinus sylvestris (Vanhatalo et al, 2018) and Rosmarinus officinalis (Peñuelas and Llusià, 1997). The observed reduced amounts of many other terpenoids in needles of thermally stressed PO which were not found in the in vitro enzyme assays, might be due to emission losses of these compounds from leaf internal storage pools during the initial phases of the experiment.…”

“…temperature, light, air humidity) and biotic factors (e.g. herbivory), as well as plant internal factors such as stomatal conductance (Niinemets et al, 2002;Niinemets and Reichstein, 2003;Ghirardo et al, 2012;Vanhatalo et al, 2018). Since δ 13 C-signatures of needles of the same experimental trees were slightly increased by elevated temperatures and VPD (Jansen et al, 2014), stomatal conductance most likely was rather reduced due to the stress treatment.…”

“…The actual needle terpenoid contents are determined by the production rate and/or the loss of terpenoids via emission into the atmosphere (Loreto and Schnitzler, 2010). Biosynthesis of terpenoids is influenced by environmental factors such as light and temperature, and plant internal parameters such as the availability of substrates, the cellular energy and redox status, as well as TPS activities (Bohlmann et al, 1998;Hartikainen et al, 2012;Vanhatalo et al, 2018). The enzymes of the MEP pathway responsible for hemi-and monoterpene biosynthesis (Dudareva et al, 2013), show a temperature optimum around 40°C (Fischbach et al, 2000;Ghirardo et al, 2010b;Loreto and Schnitzler, 2010) and might even be stimulated if the plants are exposed to heat (Sharkey et al, 2008).…”

Comments

“…The tree phenology strongly changes in spring, which is known as an important player in changing the seasonality of BVOC emissions (e.g. (Fischbach et al, 2002;Noe et al, 2012;Grote et al, 2014;Vanhatalo et al, 2018). 8) Seasonality: I find two days of measurements of one unique tree, not representative C3 for describing seasonal emission during summer.…”