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• We analysed the ectomycorrhizal (ECM) fungal diversity in a Mediterranean old-growthQuercus ilexforest stand from Corsica (France), whereArbutus unedowas the only other ECM host.• On a 6400 m2 stand, we investigated whether oak age and host species shaped below-ground ECM diversity. Ectomycorrhizas were collected underQ. ilexindividuals of various ages (1 yr seedlings; 3–10 yr saplings; old trees) andA. unedo. They were typed by ITS–RFLP analysis and identified by match to RFLP patterns of fruitbodies, or by sequencing.• A diversity of 140 taxa was found among 558 ectomycorrhizas, with many rare taxa.Cenococcum geophilumdominated (35% of ECMs), as well as Russulaceae, Cortinariaceae and Thelephoraceae. Fungal species richness was comparable above and below ground, but the two levels exhibited< 20% overlap in fungal species composition.• Quercus ilexage did not strongly shape ECM diversity. The two ECM hosts,A. unedoandQ. ilex, tended to share few ECM species (< 15% of the ECM diversity). Implications for oak forest dynamics are discussed.New Phytologist(2005)doi: 10.1111/j.1469-8137.2005.01382.x© New Phytologist(2005) [ABSTRACT FROM AUTHOR]

The aim of this work was whether or not wodative stress had developed in dwarf shrub bilberry (Vacinium myrtillus L.) under long term exposure to enhanced levels of ultraviolet B (u. v. B.) radiation. The bilberry plants were exposed to increased u. v. B representing a 15% stratospheric ozone depletion for seven full growing seasons (1991- 1997) at Abisko, Swedish Lapland (68deg;N). The oxidative stress was assessed on leaves and stems by analysing ascorbate and glutathione concentration, and activities of the closely related enzymes ascorbate peroxidase (EC 1. 11. 1. 11) and glutathione reductase (EC 1..6. 4. 2). The affects of autumnal leaf senescence and stem cold hardening on these variables were also considered. The result showed that the treatment caused scarcely any response in the studied variables indicating that u.v B flux representing a 15% ozone depletion under clear sky condition is not sufficient to cause oxidative stress in the bilberry. It is suggested that no strain was evoked since adaptation was possible under such u.v. B increases. The studied variables did however, respond significantly to leaf senescence and especially to stem cold hardening. [ABSTRACT FROM AUTHOR]

This article presents table of contents. It also says that the wood in a living tree is protected from microbial attack by the secondary plant surface, which provides an effective barrier preventing the entry of most potential pathogens, and by constitutive and induced defence mechanisms in the bark. Although a few pathogens are able to penetrate these outer tissues directly, most xylem pathogens gain entry through wounds that expose this tissue and render in more vulnerable to attack. In functional sapwood, microbial colonization might be restricted by active defence mechanisms, or by passive microenvironmental restriction consequent upon the high water content and low availability of oxygen in healthy conductive xylem.

The patterns of distribution of calcium oxalate crystals in spruce needles have been investigated in healthy needles and those subjected to either acid precipitation (ph 2.5) or various ozone fumigations. In the acid treatment, deposits of Ca oxalate were lacking in the outer walls of the epidermal cells. Under the impact of ozone, unusual complexes of Ca oxalate crystals embedded in a matrix of callose and cellulose projected from the walls inwards into the cells, filling the lumina of epidermal and hypodermal cells completely. In mesophyll cells, the complexes projected more or less from the walls into the vacuoles. In other cases, crystals appeared within the vacuoles of mesophyll cells. In dead cells, precipitates of Ca oxalate or phosphate apparently indicate destruction of the cytoplasm after a major influx of Ca2-. It is speculated, that the physiological significance of enhanced calcium leaching has been overestimated. With regard to ozone impact, it seems that the major problem of thereby enhanced membrane permeabilities may not be an increased efflux of mineral elements, but rather an increased influx of Ca into the symplast and subsequent disturbances in metabolism. [ABSTRACT FROM AUTHOR]

Whole plant acclimation to ozone exposure in growth-chamber cultivated radish (Raphanus sativus L. cv. Cherry Belle) was investigated. The primary goal was to separate developmental from physiological ozone acclimation processes. Plants were grown for 37 days at two different lengths of ozone exposure and a control treatment. After germination, seedlings were transplanted into controlled growth chambers and exposed to daytime (10 h) ozone (0.12 μl l-1) either on the next day (continuous ozone treatment) or three days later (intermediate treatment) and compared to a control (average ambient ozone concentration 0.01-0.02 μl l-1). Plants grown in ozone after transplanting accumulated considerably less biomass than the controls, but had higher dry weights than the intermediate treatment, implying an acclimation response. Photosynthetic capacity and nitrogen content of leaves decreased at high levels of ozone exposure resulting in an accelerated leaf senescence. No distinct leaf-level physiological acclimation to ozone exposure was seen based on gas exchange measurements. As an apparent compensatory response, plants exposed to ozone had higher leaf production rates than control plants, at the expense of root and hypocotyl growth. This developmental, whole-plant response appeared to be the most effective acclimation response to ozone exposure seen in radish. However, it did not fully compensate for the damage caused by ozone, since plants still showed considerable reductions in growth. [ABSTRACT FROM AUTHOR]