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We applied two tandem differential mobility analyzer methods to shed light on the evolution of the nucleation- and Aitken-mode-particle compositions at a virgin boreal-forest site during nucleation events in varying conditions. The overall results show a clear anthropogenic influence on the nucleation- and Aitken-mode-particle compositions during the events. The SO2/MTOP and NOx/MTOP (monoterpene oxidation products) ratios best explain the variation in the nucleation mode composition dining clean and pollution affected events, suggesting also the importance of organic sulfur compounds, in addition to other sulfur, nitrogen and organic compounds, in particle formation, composition and properties. During the cleanest events, MTOP explain well the time behaviour of the 10-nm particle composition with an estimated organic fraction of over 95%. [ABSTRACT FROM AUTHOR]

In greenhouse experiments, selenium (Se) has been shown to defend plants against detrimental effects of heavy UV-B radiation stress. The aim of this study was to investigate whether this positive effect can be found in open-field conditions with enhancement of UV-B radiation. In the experiment, conducted with strawberry ( Fragaria× ananassa, cultivars “Jonsok” and “Polka”) over two growing seasons, plants were exposed to UV-B radiation (including UV-A) and cultivated without Se or supplied with Se added at two levels (0.1 and 1.0 mg kg−1). The plants were monitored for growth, flavonoids, chlorophyll fluorescence, net photosynthesis as well as tissue and cell structure. Photosystem II was observed to be sensitive to UV-B stress under field conditions. In the leaves, a decrease in F v/ F m was seen at the end of the growing season, implying a cumulative effect of UV-B stress. Several parameters, especially cell and tissue structures, were affected by UV-B and UV-A treatments, which proves the need for UV-A control in outdoor UV-B supplementation studies. Addition of Se did not ameliorate the harmful effects of UV-B but the lower Se-increment level increased leaf growth. The effects of UV-B and Se differed during the two experimental years, indicating the need to repeat experiments during several growing seasons. [ABSTRACT FROM AUTHOR]

Scots pine (Pinus sylvestrisL., Pinaceae) produces a terpenoid resin which consists of monoterpenes and resin acids that offer protection against herbivores and pathogen attacks. Methyl jasmonate (MJ) is a potential plant elicitor which induces a wide range of chemical and anatomical defence reactions in conifers and might be used to increase resistance against biotic damage. Different amounts of MJ (control, 10 mm, and 100 mm) were applied to Scots pine to examine the vigour, physiology, herbivory performance, and induction of secondary compound production in needles, bark, and xylem of 2-year-old Scots pine seedlings. Growth decreased significantly in both MJ treated plants, and photosynthesis decreased in the 100 mmMJ treated plants, when compared to 10 mmMJ or control plants. The large pine weevil (Hylobius abietisL.) (Coleoptera: Curculionidae) gnawed a significantly smaller area of stem bark in the 100 mmtreated plants than in the control or 10 mmtreated plants. The 100 mmMJ treatment increased the resin acid concentration in the needles and xylem but not in the bark. Furthermore, both MJ treatments increased the number of resin ducts in newly developing xylem. The changes in plant growth and chemical parameters after the MJ treatments indicate shifts in carbon allocation, but MJ also affects plant physiology and xylem development. Terpenoid resin production was tissue-specific, but generally increased after MJ treatments, which means that this compound may offer potential protection of conifers against herbivores. [ABSTRACT FROM AUTHOR]