Cytokiningehalte von Fichtennadeln (Picea abies [L.] Karst.) nach Inokulation mit zwei Stämmen des MykorrhizapilzesThelephora terrestris (Ehrh.) Fr

CASIROZ: Root parameters and types of ectomycorrhiza of young beech plants exposed to different ozone and light regimes

Tropospheric ozone (O(3)) triggers physiological changes in leaves that affect carbon source strength leading to decreased carbon allocation below-ground, thus affecting roots and root symbionts. The effects of O(3) depend on the maturity-related physiological state of the plant, therefore adult and young forest trees might react differently. To test the applicability of young beech plants for studying the effects of O(3) on forest trees and forest stands, beech seedlings were planted in containers and exposed for two years in the Kranzberg forest FACOS experiment (Free-Air Canopy O(3) Exposure System, http://www.casiroz.de ) to enhanced ozone concentration regime (ambient [control] and double ambient concentration, not exceeding 150 ppb) under different light conditions (sun and shade). After two growing seasons the biomass of the above- and below-ground parts, beech roots (using WinRhizo programme), anatomical and molecular (ITS-RFLP and sequencing) identification of ectomycorrhizal types and nutrient concentrations were assessed. The mycorrhization of beech seedlings was very low ( CA. 5 % in shade, 10 % in sun-grown plants), no trends were observed in mycorrhization (%) due to ozone treatment. The number of Cenococcum geophilum type of ectomycorrhiza, as an indicator of stress in the forest stands, was not significantly different under different ozone treatments. It was predominantly occurring in sun-exposed plants, while its majority share was replaced by Genea hispidula in shade-grown plants. Different light regimes significantly influenced all parameters except shoot/root ratio and number of ectomycorrhizal types. In the ozone fumigated plants the number of types, number of root tips per length of 1 to 2 mm root diameter, root length density per volume of soil and concentration of Mg were significantly lower than in control plants. Trends to a decrease were found in root, shoot, leaf, and total dry weights, total number of root tips, number of vital mycorrhizal root tips, fine root (mass) density, root tip density per surface, root area index, concentration of Zn, and Ca/Al ratio. Due to the general reduction in root growth indices and nutrient cycling in ozone-fumigated plants, alterations in soil carbon pools could be predicted.

Effects of long-term, free-air ozone fumigation on the cytokinin content of mature beech trees

We present the results of a study of the effects of chronic exposure to elevated ozone on the cytokinins of mature beech trees. Methods for analysing the cytokinin (CK) content of beech (FAGUS SYLVATICA) were developed using seven enzyme-linked immunosorbent assays (ELISAs). Samples taken during 2003 and 2004 from 10 mature beech trees in Kranzberg forest, 5 trees exposed to twice ambient ozone (2 x O(3)) by free-air fumigation and 5 control trees (1 x O(3)), were analysed. In 2003 and 2004 the cytokinin content of leaf samples followed a similar seasonal pattern. In leaf samples, the content of aromatic types was equal to that of the isoprenoid types. In root samples, the level of aromatic types was no different from leaves, but that of the isoprenoid types was much higher. Leaf and phloem cytokinin contents for 2 x O(3) trees were lower than for 1 x O(3) at almost all sampling times. The effect of ozone was greater for leaves in the sun crown than for leaves in the shade crown. By contrast, the root and xylem contents of cytokinin for 2 x O(3) trees were greatly elevated over the values for 1 x O(3) trees early in the growing season. We propose that O(3)-associated CK destruction in leaves reduces CK-mediated root growth suppression. The resulting increases in root growth and ectomycorrhiza, reported by other groups in the Kranzberg forest project, are likely to be responsible for the increased CK export in xylem, although O(3)-associated CK destruction in the leaves appears to nullify this increase.

Changes in the community of ectomycorrhizal fungi and increased fine root number under adult beech trees chronically fumigated with double ambient ozone concentration

Forest soils are an important but under-studied part of forest ecosystems. The effects of O(3) on below-ground processes in a mature forest have only received limited attention so far. In our study, we have analysed the community of ectomycorrhizal fungi and beech fine root dynamics over two growing seasons (2003 - 2004) in a 70-year old mixed spruce-beech forest stand, in which two groups of five adult beech trees were either fumigated by 2 x ambient ozone concentration or used as control. The main difference between previous studies and our approach was that previous studies were performed on seedlings in pot experiments or in closed or open top chambers, and not IN SITU, in a mature forest stand. Although beech is a relatively unresponsive species to tropospheric O(3), we found a pronounced effect of 2 x O(3) on the number of vital ectomycorrhizal root tips and non-turgescent fine roots. Both categories of roots were significantly increased when compared to controls in two consecutive years at each sampling event. The number of types of ectomycorrhizae and species richness increased in 2004, but not in the extremely dry year 2003. We hypothesised that the observed changes might be an expression of a transitional state in below-ground succession of niches caused by an O(3) induced effect on carbon allocation to roots and the rhizosphere. We have detected changes in ectomycorrhizal species level, however Shannon-Weavers species diversity index and percentage of types of ectomycorrhizae did not change significantly in any sampling year thus indicating our results cannot be unequivocally explained by summer drought in year 2003 or by O(3) exposure alone.