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 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. In this study, 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. The 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 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.
Highlights
The evergreen foliage of conifers needs to acclimate to severe stresses under boreal winter conditions, including low minimum temperatures, low light availability and repeated freeze–thaw cycles
We examined the effect of seasonality and needle age on monoterpene synthase (MTS) activity, monoterpene storage pools and emissions in detail, and found that monoterpene synthases (MTS) activities were highly dependent on needle age and season (Figs. 3, 4)
Δ-3carene dynamics appeared to be strongly related to needle age: this compound was synthesized in greater amounts in the needles only during their growth and maturation (Fig. 4)
Summary
The evergreen foliage of conifers needs to acclimate to severe stresses under boreal winter conditions, including low minimum temperatures, low light availability and repeated freeze–thaw cycles. This acclimation is manifested in both structural and metabolic adjustments of needles. The spring dehardening of coniferous trees is closely linked to physiological changes related to the onset of growth, whereas hardening in the autumn results from the gradual downregulation of cellular metabolism, largely triggered by changes in temperature and the light environment (Hänninen and Tanino, 2011). A. Vanhatalo et al.: Long-term dynamics of monoterpene synthase activities ondary metabolism of needles, including the synthesis of volatile compounds, shows a seasonal pattern that reflects their physiological state Vanhatalo et al.: Long-term dynamics of monoterpene synthase activities ondary metabolism of needles, including the synthesis of volatile compounds, shows a seasonal pattern that reflects their physiological state (e.g. Fischbach et al, 2002; Jaakola and Hohtola, 2010)
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