Competition in mixed stands of beech and spruce: effects of climate and ozone

Abstract

The “Growth-DiVerentiation Balance Theory” assumes a trade-oV between parasite defense and increases in growth and competitiveness (Herms and Mattson 1992). Accordingly, increasing resource availability would induce a decrease in secondary metabolites, and hence defense capacity, relative to primary production. Since 1998, about 20 research teams have examined this theory in the interdisciplinary research center “Sonderforschungsbereich 607” (SFB 607), being conducted in Munich and FreisingWeihenstephan (Germany; Matyssek et al. 2005). In this issue, they present results from studies focusing on the eVects of ozone and drought stress on beech and spruce competing in mixed stands. The mature stand as one research object of the reported studies is “Kranzberger Forst”, a 55-year-old Norway spruce stand near Freising/Germany with groups of 62year-old beech. From the year 2000 on, a group of beech and spruce trees has been exposed to experimentally enhanced free-air ozone fumigation (Karnosky et al. 2001). Ozone was applied, through a novel methodological approach, via more than 100 PTFE tubes into the stand canopy in such a way that Wve spruce and Wve beech trees were exposed to a twice-ambient ozone regime, with ozone levels being restricted to below 150 nl li1 (Nunn et al. 2002; Werner and Fabian 2002; Karnosky et al. 2007). The Wrst paper introduces a novel approach to study the hydraulic architecture of coarse roots. Nikolova et al. (2008b, this issue) combined computer tomography, light microscopy, and sap Xow measurements in order to anatomically and functionally compare the conductive sapwood area of coarse roots between beech and spruce. Cumulative sapwood lumen area was 12% of the total coarse root cross-sectional area in both species. Normalized by that parameter, sap Xow rate increased with root diameter. Haberle et al. (2008, this issue) tested a conceptual approach to assess the amount of carbon available for trade-oVs between defense and growth. They monitored the variation in levels of nine defense-related metabolite groups within and between four consecutive growing seasons in mature beech and spruce trees. The diVerence between minimum and maximum metabolite levels was assumed to be dispensable between growth and defenserelated metabolism, ranging between 2 and 5% of gross primary production. A set of papers describes the eVects of ozone and drought, especially during the extreme summer of 2003. Betz et al. (2008, this issue) investigating the shikimate pathway in the greenhouse and in the Weld, caution against uncritical comparisons between greenhouse-grown saplings and mature forest trees. Rodenkirchen et al. (2008, this issue) studied the eVects of ozone and CO2 on the competitiveness of beech and spruce saplings under standardized phytotron conditions. Ozone stress reduced nutrient eYciencies in beech, suggesting a higher demand for N and P in defense at the expense of competitiveness. Elevated CO2 counteracted the eVects of ozone. In mature ozonefumigated trees, the extreme summer of 2003 had no eVect on the concentrations of P and K in the leaves, whereas the control trees had signiWcantly lower levels of these nutrients in 2004 (Gottlein et al. 2008, this issue). Although ozone fumigation reduced absolute tree diameter increment at breast height in spruce, there was no such eVect in beech S. Rust · A. RoloV (&) Institut fur Forstbotanik und Forstzoologie, TU Dresden, Postfach 1117, 01735 Tharandt, Germany e-mail: roloV@forst.tu-dresden.de