Forests under climate change and air pollution: gaps in understanding and future directions for research.

Forests in Europe face significant changes in climate, which in interaction with air quality changes, may significantly affect forest productivity, stand composition and carbon sequestration in both vegetation and soils. Identified knowledge gaps and research needs include: (i) interaction between changes in air quality (trace gas concentrations), climate and other site factors on forest ecosystem response, (ii) significance of biotic processes in system response, (iii) tools for mechanistic and diagnostic understanding and upscaling, and (iv) the need for unifying modelling and empirical research for synthesis. This position paper highlights the above focuses, including the global dimension of air pollution as part of climate change and the need for knowledge transfer to enable reliable risk assessment. A new type of research site in forest ecosystems ("supersites") will be conducive to addressing these gaps by enabling integration of experimentation and modelling within the soil-plant-atmosphere interface, as well as further model development.

Metabolic-dependent changes in plant cell redox power after ozone exposure.

The tropospheric level of the phytotoxic air pollutant ozone has increased considerably during the last century, and is expected to continue to rise. Long-term exposure of higher plants to low ozone concentrations affects biochemical processes prior to any visible symptoms of injury. The current critical level of ozone used to determine the threshold for damaging plants (biomass loss) is still based on the seasonal sum of the external concentration above 40 nl.l(-1) (AOT40). Taking into account stomatal conductance and the internal capacity of leaf defences, a more relevant concept should be based upon the 'effective ozone flux', the balance between the stomatal flux and the intensity of cellular detoxification. The large decrease in the Rubisco/PEPc ratio reflects photosynthetic damage from ozone, and a large increase in activity of cytosolic PEPc, which allows increased malate production. Although the direct detoxification of ozone (and ROS produced from its decomposition) is carried out primarily by cell wall ascorbate, the existing level of this antioxidant is not sufficient to indicate the degree of cell sensitivity. In order to regenerate ascorbate, NAD(P)H is needed as the primary supplier of reducing power. It is hypothesised that increased activity of the catabolic pathways and associated shunts (glucose-6-phosphate dehydrogenase, NADP-dependent glyceraldehyde-3-phosphate dehydrogenase, isocitrate dehydrogenase and malic enzyme) can provide sufficient NAD(P)H to maintain intracellular detoxification. Thus, measurement of the level of redox power would contribute to determination of the 'effective ozone dose', serving ultimately to improve the ozone risk index for higher plants.

Bituminous emulsions and their characterization by atomic force microscopy

We present a new method for observing oil-in-water emulsions with a continuous water phase and a dispersed bitumen phase. The fine polydispersed bitumen micelles were adsorbed to an atomically smooth mica substrate and imaged in solution by atomic force microscopy in a liquid cell. The height of the adsorbed bitumen sheet in wet and dry states can be measured and the homogeneity of film formation by coalescence can be determined. Localization of surfactant onto and between bitumen micelles is also visualized.

Changes in Properties of Barley Leaf Mitochondria Isolated from NaCl-Treated Plants.

Treatment of barley (Hordeum vulgare) seedlings with 400 millimolar NaCl for 3 days resulted in a reduction in plant growth and an increase in the leaf content in ions (K(+) + Na(+)) and proline. Purified mitochondria were successfully isolated from barley leaves. Good oxidative and phosphorylative properties were observed with malate as substrate. Malate-dependent electron transport was found to be only partly inhibited by cyanide, the remaining oxygen uptake being SHAM sensitive. The properties of mitochondria from NaCl-treated barley were modified. The efficiency of phosphorylation was diminished with only a slight decrease in the oxidation rates. In both isolated mitochondria and whole leaf tissue of treated plants, the lower respiration rate was due to a lower cytochrome pathway activity. In mitochondria, the activity of the alternative pathway was not modified by salt treatment, whereas this activity was increased in whole leaf tissue. The possible participation of the alternative pathway in response to salt stress will be discussed.