Needle metabolome, freezing tolerance and gas exchange in Norway spruce seedlings exposed to elevated temperature and ozone concentration

Abstract

Northern forests are currently experiencing increasing mean temperatures, especially during autumn and spring. Consequently, alterations in carbon sequestration, leaf biochemical quality and freezing tolerance (FT) are likely to occur. The interactive effects of elevated temperature and ozone (O3), the most harmful phytotoxic air pollutant, on Norway spruce (Picea abies (L.) Karst.) seedlings were studied by analysing phenology, metabolite concentrations in the needles, FT and gas exchange. Sampling was performed in September and May. The seedlings were exposed to a year-round elevated temperature (+1.3°C), and to 1.4× ambient O3 concentration during the growing season in the field. Elevated temperature increased the concentrations of amino acids, organic acids of the citric acid cycle and some carbohydrates, and reduced the concentrations of phenolic compounds, some organic acids of the shikimic acid pathway, sucrose, cyclitols and steroids, depending on the timing of the sampling. Although growth onset occurred earlier at elevated temperature, the temperature of 50 lethality (LT50) was similar in the treatments. Photosynthesis and the ratio of photosynthesis to dark respiration were reduced by elevated temperature. Elevated concentrations of O3 reduced the total concentration of soluble sugars, and tended to reduce LT50 of the needles in September. These results show that alterations in needle chemical quality can be expected at elevated temperatures, but the seedlings' sensitivity to autumn and spring frosts is not altered. Elevated O3 has the potential to disturb cold hardening of Norway spruce seedlings in autumn, and to alter the water balance of the seedling through changes in stomatal conductance (gs), while elevated temperature is likely to reduce gs and consequently reduce the O3-flux inside the leaves. © 2012 The Author.