 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.plant-soil.com 408 DOI: 10.1002/jpln.200900351 J. Plant Nutr. Soil Sci. 2011, 174, 408–419 Soil base saturation affects root growth of European beech seedlings § Anika K. Richter 1,4 *, Yasuhiro Hirano 2 , Jörg Luster 1 , Emmanuel Frossard 3 , and Ivano Brunner 1 1 Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zürcherstraße 111, 8903 Birmensdorf, Switzerland 2 Earth Environmental Systems, Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa, Nagoya 464–8601, Japan 3 Institute of Plant Science, ETH Zürich, Eschikon 33, 8315 Lindau, Switzerland 4 Current address: Uferstraße 18, 42799 Leichlingen, Germany Abstract To assess the potential effects of Al toxicity on the roots of young European beech (Fagus sylva- tica L.), seeds were sown in soil monoliths taken from the Ah and B horizons of forest soils with very low base saturation (BS) and placed in the greenhouse. The Ah horizons offered a larger supply of exchangeable cation nutrients than the B horizons. After 8 weeks of growth under opti- mal moisture conditions, the seedlings were further grown for 14 d under drought conditions. Root-growth dynamics were observed in rhizoboxes containing soils from the Ah and B hori- zons. The concentrations of Al 3+ , base cations, and nitrate in the soil solution and element con- centrations in the root tissue were compared with above- and belowground growth parameters and root physiological parameters. There was no strong evidence that seedling roots suffered from high soil-solution Al 3+ concentrations. Within the tested range of BS (1.2%–6.5%) our results indicated that root physiological parameters such as O 2 consumption decreased and cal- lose concentration increased in soils with a BS < 3%. In contrast to the B horizons, seedlings in the Ah horizons had higher relative shoot-growth rates, specific root lengths, and lengths and branching increments, but a lower root-to-shoot ratio and root-branching frequency. In conclu- sion, these differences in growth patterns were most likely due to differences in nutrient availabil- ity and to the drought application and not attributable to differences in Al 3+ concentrations in the soil solution. Key words: aluminium toxicity / Ca : Al molar ratio / callose / O 2 consumption / root morphology / root-to-shoot ratio Accepted July 23, 2010 1 Introduction Acid depositions have accelerated the acidification process of forest soils for many years, although their rates declined in Europe through the 1980s and 1990s (Blaser et al., 1999; Jönsson et al., 2003; Graf Pannatier et al., 2004). For instance, such enhanced acidification can alter habitats and, therefore, have ecological consequences for forest ecosys- tems. Acidification may result in decreased rejuvenation and seedling growth of forest trees (Ljungström and Stjernquist, 1993). Soil acidification below a pH of 5 is accompanied, on one hand, by increased weathering of Al from soil minerals and, on the other hand, by a decrease in base saturation (BS) in the soil matrix as Al competes with essential base cations (BC = K, Mg, Ca) on the soil exchanger leading to an enhanced leaching of BC from the soil and a decrease of the BC : Al molar ratio in the soil solution (Jönsson et al., 2003; Walthert et al., 2004). The BC : Al molar ratio in soil solution provides a good indication for how roots are distributed within a soil (Jentschke et al., 2001; Sverdrup and Warfvinge, 1993). Low concentrations of BC in soil solution mainly lead to deficiencies in essential elements, and, in acidic soils, to elevated Al contents in the root tissues (Göransson and Eldhuset, 1995; Zysset et al., 1996). Low BC linked with high Al 3+ concentrations in the soil solution can potentially affect the root morphology (Godbold et al., 1988; Clemensson-Lindell and Persson, 1995; Godbold et al., 2003). Moreover, low BS in the soil solid phase can lead to low base- cation concentrations in the soil solution, subsequently affecting root physiology and chemistry (Hirano and Brunner , 2006; Richter et al., 2007b). Physiological properties such as the roots’ respiratory activity (Comas et al., 2000; Richter et al., 2007a, b), their uptake rate of essential nutrient elements (Göransson and Eldhuset, 1991; Nygaard and de Wit, 2004; Vanguelova et al., 2005; Richter et al., 2007b), and the callose concentration in root apices (Hirano et al., 2004, 2006) can serve as indicators of the health status of roots. Changes in root morphology, physiology, and chemistry may also affect shoot growth. Baligar and Fageria (2005) showed that aboveground biomass development was altered due to BC leaching from the soil and Al 3+ toxicity. An adverse soil chemical status can lead to changes in biomass partitioning between the * Correspondence: Dr. A. Richter; e-mail: anikarichter@freenet.de § The manuscript is part of the PhD thesis by Anika Richter, entitled “Fine roots of trees – effects of soil acidification on their vitality”, ETH Zürich; Swiss Federal Institute for Forest Snow and Landscape Research WSL