Impacts of ozone and CO 2 enrichment, alone and in combination, on leaf anatomical and ultrastructural characteristics, nutrient status and cell wall chemistry in two European silver birch (Betula pendula Roth) clones were studied. The young soil-growing trees were exposed in open-top chambers over three growing seasons to 2 Â ambient CO 2 and/ or ozone concentrations in central Finland. The trees were measured for changes in altogether 35 variables of leaf structure, nutrients and cell wall chemistry of green leaves, and 20 of the measured variables were affected by CO 2 and/or O 3 . Elevated CO 2 increased the size of chloroplasts and starch grains, number of mitochondria, P : N ratio, and contents of cell wall hemicellulose. Elevated CO 2 decreased the total leaf thickness, specific leaf area, concentrations of N, K, Cu, S and Fe, and contents of cell wall a-cellulose, uronic acids, acid-soluble lignin and acetone-soluble extractives. Elevated ozone led to thinner leaves, higher palisade to spongy ratio, increased number of peroxisomes and mitochondria, reduced content of Mn, Zn, Cu, hemicellulose and uronic acids, and lower Mn : N and Zn : N ratios. In the combined exposure, interactions were antagonistic. Ultrastructural changes became more evident towards the end of the exposure. Young leaves were tolerant against ozone-caused oxidative stress, whereas oxidative H 2 O 2 accumulation was found in older leaves. CO 2 enrichment improved ozone tolerance not only through increased photosynthesis rates, but also through changes in cell wall chemistry (hemicellulose, in particular). However, nutrient imbalances due to ozone and/or CO 2 may predispose the trees to other biotic and abiotic stresses. Down-regulation and up-regulation of photosynthesis under elevated CO 2 through anatomical changes is discussed.
The aim of this study was to examine the effects of elevated carbon dioxide [CO 2 ] and ozone [O 3 ] and their interaction on wood chemistry and anatomy of five clones of 3-yearold trembling aspen (Populus tremuloides Michx.). Wood chemistry was studied also on paper birch (Betula papyrifera Marsh.) and sugar maple (Acer saccharum Marsh.) seedling-origin saplings of the same age. Material for the study was collected from the Aspen Free-Air CO 2 Enrichment (FACE) experiment in Rhinelander, WI, USA, where the saplings had been exposed to four treatments: control (C; ambient CO 2 , ambient O 3 ), elevated CO 2 (560 ppm during daylight hours), elevated O 3 (1.5 Â ambient during daylight hours) and their combination (CO 2 1 O 3 ) for three growing seasons (1998)(1999)(2000). Wood chemistry responses to the elevated CO 2 and O 3 treatments differed between species. Aspen was most responsive, while maple was the least responsive of the three tree species. Aspen genotype affected the responses of wood chemistry and, to some extent, wood structure to the treatments. The lignin concentration increased under elevated O 3 in four clones of aspen and in birch. However, elevated CO 2 ameliorated the effect. In two aspen clones, nitrogen in wood samples decreased under combined exposure to CO 2 and O 3 . Soluble sugar concentration in one aspen clone and starch concentration in two clones were increased by elevated CO 2 . In aspen wood, a-cellulose concentration changed under elevated CO 2 , decreasing under ambient O 3 and slightly increasing under elevated O 3 . Hemicellulose concentration in birch was decreased by elevated CO 2 and increased by elevated O 3 . In aspen, elevated O 3 induced statistically significant reductions in distance from the pith to the bark and vessel lumen diameter, as well as increased wall thickness and wall percentage, and in one clone, decreased fibre lumen diameter. Our results show that juvenile wood properties of broadleaves, depending on species and genotype, were altered by atmospheric gas concentrations predicted for the year 2050 and that CO 2 ameliorates some adverse effects of elevated O 3 on wood chemistry.
The objective of the present study was to investigate the interactive effects of elevated [CO 2 ] and soil nutrient availability on secondary xylem structure and chemical composition of 41-year-old Norway spruce (Picea abies (L.) Karst.) trees. The nonfertilized and irrigated-fertilized trees were, for 3 years, continuously exposed to elevated [CO 2 ] in whole-tree chambers. Elevated [CO 2 ] decreased concentrations of soluble sugars, acid-soluble lignin and nitrogen in stem wood, but the effects were not consistent between sampling height and/or fertilization. The effect of 2*ambient [CO 2 ] on wood structure depended on the exposure year and/or fertilization. Radial lumen diameter decreased and annual ring width increased in the second year of exposure (1999) in elevated [CO 2 ]. In the latter, the CO 2 effect was significant only in the nonfertilized trees. Stem wood chemistry and structure were significantly affected by fertilization. Fertilization increased the concentrations of nitrogen and gravimetric lignin, annual ring width, and radial lumen diameter. Fertilization decreased C/N ratio, mean ring density, earlywood density, latewood density, cell wall thickness, cell wall index, and latewood percentage. We conclude that elevated [CO 2 ] had only minor effects on wood properties while fertilization had more marked effects and thus may affect ecosystem processes and suitability of wood for different end-use purposes.
The objective of the study was to investigate the interactive effects of elevated atmospheric carbon dioxide concentration, [CO 2 ], and temperature on the wood properties of mature field-grown Norway spruce (Picea abies (L.) Karst.) trees. Material for the study was obtained from an experiment in Flakaliden, northern Sweden, where trees were grown for 3 years in whole-tree chambers at ambient (365 lmol mol À1 ) or elevated [CO 2 ] (700 lmol mol À1 ) and ambient or elevated air temperature (ambient 1 5.6 1C in winter and ambient 1 2.8 1C in summer). Elevated temperature affected both wood chemical composition and structure, but had no effect on stem radial growth. Elevated temperature decreased the concentrations of acetone-soluble extractives and soluble sugars, while mean and earlywood (EW) cell wall thickness and wood density were increased. Elevated [CO 2 ] had no effect on stem wood chemistry or radial growth. In wood structure, elevated [CO 2 ] decreased EW cell wall thickness and increased tracheid radial diameter in latewood (LW). Some significant interactions between elevated [CO 2 ] and temperature were found in the anatomical and physical properties of stem wood (e.g. microfibril angle, and LW cell wall thickness and density). Our results show that the wood material properties of mature Norway spruce were altered under exposure to elevated [CO 2 ] and temperature, although stem radial growth was not affected by the treatments.
One-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were grown hydroponically in a growth chamber to investigate the effects of low and high nutrient availability (LN; 0.25 mM N and HN; 2.50 mM N) on growth, biomass allocation and chemical composition of needles, stem and roots during the second growing season. Climatic conditions in the growth chamber simulated the mean growing season from May to early October in Flakaliden, northern Sweden. In the latter half of the growing season, biomass allocation changed in response to nutrient availability: increased root growth and decreased shoot growth led to higher root/shoot ratios in LN seedlings than in HN seedlings. At high nutrient availability, total biomass, especially stem biomass, increased, as did total nonstructural carbohydrate and nitrogen contents per seedling. Responses of stem chemistry to nutrient addition differed from those of adult trees of the same provenance. In HN seedlings, concentrations of alpha-cellulose, hemicellulose and lignin decreased in the secondary xylem. Our results illustrate the significance of retranslocation of stored nutrients to support new growth early in the season when root growth and nutrient uptake are still low. We conclude that nutrient availability alters allocation patterns, thereby influencing the success of 2-year-old Norway spruce seedlings at forest planting sites.
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