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To study the effects of slightly elevated temperature and ozone (O3) on leaf structural characteristics of silver birch (Betula pendula Roth), saplings of four clonal genotypes of this species were exposed to elevated temperature (ambient air temperature +0.8–1.0 °C) and elevated O3 (1.3–1.4× ambient O3), alone and in combination, in an open-air exposure field over two growing seasons (2007 and 2008). So far, the impacts of moderate elevation of temperature or the combination of elevated temperature and O3 on leaf structure of silver birch have not been intensively studied, thus showing the urgent need for this type of studies. Elevated temperature significantly increased leaf size, reduced non-glandular trichome density, decreased epidermis thickness and increased plastoglobuli size in birch leaves during one or both growing seasons. During the second growing season, O3 elevation reduced leaf size, increased palisade layer thickness and decreased the number of plastoglobuli in spongy cells. Certain leaf structural changes observed under a single treatment of elevated temperature or O3, such as increase in the amount of chloroplasts or vacuole, were no longer detected at the combined treatment. Leaf structural responses to O3 and rising temperature may also depend on timing of the exposure during the plant and leaf development as indicated by the distinct changes in leaf structure along the experiment. Genotype-dependent cellular responses to the treatments were detected particularly in the palisade cells. Overall, this study showed that even a slight but realistic elevation in ambient temperature can notably modify leaf structure of silver birch saplings. Leaf structure, in turn, influences leaf function, thus potentially affecting acclimation capacity under changing climate. [ABSTRACT FROM AUTHOR]

In the present experiment, the single and combined effects of elevated temperature and ozone (O3) on four silver birch genotypes (gt12, gt14, gt15 and gt25) were studied in an open-air field exposure design. Above- and below-ground biomass accumulation, stem growth and soil respiration were measured in 2008. In addition, a 13C-labelling experiment was conducted with gt15 trees. After the second exposure season, elevated temperature increased silver birch above- and below-ground growth and soil respiration rates. However, some of these variables showed that the temperature effect was modified by tree genotype and prevailing O3 level. For instance, in gt14 soil respiration was increased in elevated temperature alone (T) and in elevated O3 and elevated temperature in combination (O3 + T) treatments, but in other genotypes O3 either partly (gt12) or totally nullified (gt25) temperature effects on soil respiration, or acted synergistically with temperature (gt15). Before leaf abscission, all genotypes had the largest leaf biomass in T and O3 + T treatments, whereas at the end of the season temperature effects on leaf biomass depended on the prevailing O3 level. Temperature increase thus delayed and O3 accelerated leaf senescence, and in combination treatment O3 reduced the temperature effect. Photosynthetic : non-photosynthetic tissue ratios (P : nP ratios) showed that elevated temperature increased foliage biomass relative to woody mass, particularly in gt14 and gt12, whereas O3 and O3 + T decreased it most clearly in gt25. O3-caused stem growth reductions were clearest in the fastest-growing gt14 and gt25, whereas mycorrhizal root growth and sporocarp production increased under O3 in all genotypes. A labelling experiment showed that temperature increased tree total biomass and hence 13C fixation in the foliage and roots and also label return was highest under elevated temperature. Ozone seemed to change tree 13C allocation, as it decreased foliar 13C excess amount, simultaneously increasing 13C excess obtained from the soil. The present results suggest that warming has potential to increase silver birch growth and hence carbon (C) accumulation in tree biomass, but the final magnitude of this C sink strength is partly counteracted by temperature-induced increase in soil respiration rates and simultaneous O3 stress. Silver birch populations' response to climate change will also largely depend on their genotype composition. [ABSTRACT FROM AUTHOR]

Rising temperature and tropospheric ozone (O3) concentrations are likely to affect carbon assimilation processes and thus the carbon sink strength of trees. In this study, we investigated the joint action of elevated ozone and temperature on silver birch (Betula pendula) and European aspen (Populus tremula) saplings in field conditions by combining free-air ozone exposure (1.2 × ambient) and infrared heaters (ambient +1.2 °C). At leaf level measurements, elevated ozone decreased leaf net photosynthesis (Pn), while the response to elevated temperature was dependent on leaf position within the foliage. This indicates that leaf position has to be taken into account when leaf level data are collected and applied. The ozone effect on Pn was partly compensated for at elevated temperature, showing an interactive effect of the treatments. In addition, the ratio of photosynthesis to stomatal conductance (Pn/gs ratio) was decreased by ozone, which suggests decreasing water use efficiency. At the plant level, the increasing leaf area at elevated temperature resulted in a considerable increase in photosynthesis and growth in both species. [ABSTRACT FROM PUBLISHER]

Volatile organic compounds (VOCs) are expected to have an important role in plant adaptation to high temperatures. The impacts of increasing night-time temperature on daytime terpenoid emissions and related gene expression in silver birch (Betula pendula) and European aspen (Populus tremula) clones were studied. The plants were grown under five different night-time temperatures (6, 10, 14, 18, and 22 °C) while daytime temperature was kept at a constant 22 °C. VOC emissions were collected during the daytime and analysed by gas chromatography–mass spectrometry (GC-MS). In birch, emissions per leaf area of the C11 homoterpene 4,8-dimethy1-nona-1,3,7-triene (DMNT) and several sesquiterpenes were consistently increased with increasing night-time temperature. Total sesquiterpene (SQT) emissions showed an increase at higher temperatures. In aspen, emissions of DMNT and β-ocimene increased from 6 °C to 14 °C, while several other monoterpenes and the SQTs (Z,E)-α-farnesene and (E,E)-α-farnesene increased up to 18 °C. Total monoterpene and sesquiterpene emission peaked at 18 °C, whereas isoprene emissions decreased at 22 °C. Leaf area increased across the temperature range of 6–22 °C by 32% in birch and by 59% in aspen. Specific leaf area (SLA) was also increased in both species. The genetic regulation of VOC emissions seems to be very complex, as indicated by several inverse relationships between emission profiles and expression of several regulatory genes (DXR, DXS, and IPP). The study indicates that increasing night temperature may strongly affect the quantity and quality of daytime VOC emissions of northern deciduous trees. [ABSTRACT FROM PUBLISHER]

We studied the effects of slightly elevated temperature ( T), O3 concentration (O3) and their combination ( T + O3) on the antioxidant defense, gas exchange and total leaf area of Betula pendula saplings in field conditions. During the second year of the experiment, T enhanced the total leaf area, net photosynthesis ( Pn) and maximum capacity of carboxylation, redox state of ascorbate and total antioxidant capacity in the apoplast. O3 did not affect the total leaf area, but Pn was slightly and gs significantly reduced. The saplings responded to elevated O3 level by closing the stomata and by developing leaves with a lower leaf area per mass, rather than by accumulating ascorbate in the apoplast. The effects of T and O3 on total leaf area and Pn were counteractive. Elevated O3 reduced the saplings’ ability to utilize the warmer growth environment by increasing the stomatal limitation for photosynthesis and by reducing the redox state of ascorbate in the apoplast in the combination treatment as compared to T alone. [ABSTRACT FROM AUTHOR]

Abstract: Plants emit a considerable proportion of the carbon fixed by photosynthesis back into the atmosphere as volatile organic compounds (VOCs). Increasing evidence indicates that these compounds may have an important role in the adaptation of plants to changing climate, and that VOCs significantly influence atmospheric processes, such as formation of ozone (O3) and secondary organic aerosols. The effects of elevated temperature (ambient air temperature+0.8–1°C) and O3 (1.3–1.4× ambient O3), alone and in combination, on VOC emission, expression of genes related to VOC synthesis, and gas exchange were studied in four silver birch (Betula pendula Roth) clones grown in an open-air exposure field over two growing seasons. Photosynthesis and total emissions of mono-, homo- and sesquiterpenes and compounds other than terpenes [green leaf volatiles (GLVs)+methyl salicylate (MeSA)] were significantly increased and stomatal conductance decreased by temperature increase, while O3 reduced total emission of GLVs+MeSA and photosynthesis of birch. VOC emission rate corresponded with photosynthesis rate in the birch clones. Mono- and homoterpenes showed highest emission in August and GLVs+MeSA in July, whereas gas exchange decreased toward the end of the summer. In contrast to VOC emissions, transcription of genes encoding 1-deoxy-d-xylulose 5-phosphate synthase (DXS), 1-deoxy-d-xylulose 5-phosphate reductoisomerase (DXR) and isopentenyl diphosphate (IPP) isomerase at the initial stages of terpene synthesis pathway was lower at elevated temperature and higher at elevated O3. In conclusion, rising temperature will substantially increase VOC emissions from silver birch, presumably independently from stomatal conductance and partially as a consequence of increased availability of substrates due to enhanced photosynthesis. [Copyright &y& Elsevier]