Winter peridermal conductance of apple trees: lammas shoots and spring shoots compared
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ORIGINAL PAPER
Winter peridermal conductance of apple trees: lammas shoots and spring shoots compared B. Beikircher • S. Mayr
Received: 5 July 2012 / Revised: 29 November 2012 / Accepted: 3 December 2012 / Published online: 14 December 2012 Ó The Author(s) 2012. This article is published with open access at Springerlink.com
Abstract Lammas shoots are flushes formed by some woody species later in the growing season. Having less time to develop, tissue formation is suggested to be incomplete leading to a higher peridermal water loss during consecutive months. In this study, we analysed morphological and anatomical parameters, peridermal conductance to water vapour and the level of native embolism in midwinter and late-winter of lammas shoots and normal spring shoots of the apple varieties Malus domestica ‘Gala’ and ‘Nicoter’. Lammas shoots showed a significantly higher shoot cross-sectional area due to larger pith and corticular parenchyma areas. In contrast, phloem was significantly thicker in spring shoots. No pronounced differences were observed in xylem and collenchyma thickness or mean hydraulic conduit diameter. The phellem of spring shoots was composed of more suberinised cells compared to lammas shoots, which led to a significantly higher peridermal conductance in the latter. The amount of native embolism in mid-winter did not differ between shoot types, but in late-winter lammas shoots were more embolised than spring shoots. Data show that the restricted vegetation period of lammas shoots affects their development and, in consequence, their transpiration shield. This may also pose a risk for winter desiccation. Keywords Drought Embolism Freeze-thaw Growth Vulnerability Tree hydraulics Malus
Communicated by Y. Sano. B. Beikircher (&) S. Mayr Institute of Botany, University of Innsbruck, Sternwartestraße 15, 6020 Innsbruck, Austria e-mail: [email protected]
Introduction Lammas shoots are bursts of shoot growth which, in contrast to spring shoots, occur later in the growing season. Usually, woody plants of the temperate zone start their growth in spring after termination of winter dormancy and when environmental conditions are favourable. Shoots of previous year buds elongate and new buds are formed, out of which shoots develop in the following growing season (Larcher 2003). In some trees, these newly formed buds open already in the current growing season, producing a late-season burst of growth (Pallardy 2008). This phenomenon is mostly known as ‘lammas shoots’, as they often appear around Lammas day on August 1 (Evans 1972; Gue´de´s 1981; Kozlowski and Pallardy 2002; Larcher 2003; Meier 2003). However, other terms like ‘Johannis shoots’ (Kobel 1954; Lyr et al. 1967; Weinreich 2000) or ‘summer flushes’ (Sabatier and Barthe´le´my 2001) are also used and in some species, even more than two flushes per growing season can occur (Jones 1959; Barthe´le´my and Caraglio 2007; Cline and Harrington 2007; for a critical revision of terms also see Caraglio and Barthe´le´my 1997). The occurrenc
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