Carbohydrate concentrations in different plant parts of young beech and spruce along a gradient of ozone pollution
Introduction
Ozone is a widespread air pollutant, the significance of which is expected to increase in future (Fowler et al., 1999). Growth and photosynthesis of young forest trees have been affected at ambient levels (Fuhrer et al., 1997). In order to quantify the risk by ozone, the ozone load was calculated as the daylight sum of all hourly ozone values exceeding 40 ppb (AOT40) (Fuhrer et al., 1997). The critical level of AOT40 was set to 5 ppm h (Karlsson et al., 2004). This type of calculation, however, does not consider that ozone has to be taken up via the stomata (Reich, 1987) in order to damage the plants, and hence calculation of stomatal flux better describes the ozone risk. In addition, most of the experimental studies have been conducted with seedlings or young trees in chambers. The up-scaling of these results to mature trees in the field environment is a challenge for future ozone research (Fredericksen et al., 1995; Samuelson and Kelly, 2001). To facilitate this up-scaling, biochemical indicators may be useful.
Carbon allocation has been shown to be very sensitive to ozone (Spence et al., 1990; Lux et al., 1997). The aim of the present study was, therefore, to test how useful carbohydrate concentrations in different plant parts are as indicators for ozone effects for trees not grown in experimental chambers, which have both micrometeorological and physical limitations. These investigations provide a platform to enable investigation of mature forest trees.
Section snippets
Materials and methods
In summer 1996, 1-yr-old seedlings of beech and 2-yr-old spruce were potted in forest soil and placed on six sites that differed in ambient ozone concentrations (Table 1). Two of the sites are situated in a highly polluted region where visible ozone injury in native vegetation is frequently observed (VanderHeyden et al., 2001), one (spruce only) is an alpine site near the tree line. The soil, a strong acidic silty loam from a deciduous forest (pH (CaCl2) 4.3, actual base saturation 83%), was
Beech
The monosaccharide concentration in fine roots showed a decreasing trend in beech with increasing ozone dose (Fig. 2, Table 4). There is no similar relationship with temperature, irradiation, rainfall or altitude suggesting that the differences in monosaccharide concentrations can be attributed to differences in ozone. Although a significance level of 0.05 is not reached due to the low number of sites, the regression is almost significant and similar for all four ozone quantifications tested.
Discussion
The results suggest that carbohydrate concentrations in different plant compartments are useful indicators for ozone impact, although both the carbohydrate type and the indicative plant part were different for beech and spruce. Whereas in beech the monosaccharide concentration in fine roots was the best indicator for ozone, in spruce the highest correlation with increasing ozone was found for starch concentrations in plant parts other than fine roots. Starch in fine roots was negatively related
Acknowledgements
The present study was supported by the Swiss Agency for the Environment. We thank Beat Achermann and Dr. Richard Volz for their support and their interest in our work, Dr. Brigitte Buchmann from the Swiss Federal Laboratories for Materials Testing and Research for supplying us with ozone analyzers and Andreas Mebert and Roland Woeffray for maintaining the plantations. Our thanks go also to Giuseppe Tettamanti who offered us the site in Sagno (Lattecaldo), to Dr. Martin Winkler for the site on
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