Abstract
Key message Variability in xylem and phloem phenology among years and species is caused by contrasting temperatures prevailing at the start of the growing season and species-specific sensitivity to drought. The focus of this study was to determine temporal dynamics of xylem and phloem formation in co-occurring deciduous and evergreen coniferous species in a dry inner Alpine environment (750 m a.s.l., Tyrol, Austria). By repeated micro-sampling of the stem, timing of key phenological dates of xylem and phloem formation was compared among mature Pinus sylvestris, Larix decidua and Picea abies during two consecutive years. Xylem formation in P. sylvestris started in mid and late April 2011 and 2012, respectively, and in both years about 2 week later in P. abies and L. decidua. Phloem formation preceded xylem formation on average by 3 week in P. sylvestris, and c. 5 week in P. abies and L. decidua. Based on modeled cell number increase, tracheid production peaked between early through late May 2011 and late May through mid-June 2012. Phloem formation culminated between late April and mid-May in 2011 and in late May 2012. Production of xylem and phloem cells continued for about 4 and 5–6 months, respectively. High variability in xylem increment among years and species is related to exogenous control by climatic factors and species-specific sensitivity to drought, respectively. On the other hand, production of phloem cells was quite homogenous and showed asymptotic decrease with respect to xylem cells indicating endogenous control. Results indicate that onset and culmination of xylem and phloem formation are controlled by early spring temperature, whereby strikingly advanced production of phloem compared to xylem cells suggests lower temperature requirement for initiation of the former.
Highlights
The occurrence of phenological events in plant development such as bud break, leaf unfolding or flowering, is affected by climatic conditions (e.g., Chuine 2010) and several studies revealed shifts in phenological events in course of climate change (e.g., Menzel and Sparks 2006; Rutishauser et al 2008)
Key message Variability in xylem and phloem phenology among years and species is caused by contrasting temperatures prevailing at the start of the growing season and species-specific sensitivity to drought
Xylem width amounted to 0.21 mm ± 0.1 (L. decidua), 0.35 mm ± 0.2 (P. sylvestris), and 0.76 mm ± 0.2 (P. abies) in 2011 and 0.36 mm ± 0.1 (L. decidua), 0.49 mm ± 0.2 (P. sylvestris), and 1.17 mm ± 0.3 (P. abies) in 2012
Summary
The occurrence of phenological events in plant development such as bud break, leaf unfolding or flowering, is affected by climatic conditions (e.g., Chuine 2010) and several studies revealed shifts in phenological events in course of climate change (e.g., Menzel and Sparks 2006; Rutishauser et al 2008). I.e., the determination of crucial phenological stages of xylem growth, i.e., onset, maximum and end of wood formation was monitored in deciduous and coniferous trees in recent years (e.g., Rossi et al 2006b; Gruber et al 2010; Michelot et al 2012; Zhai et al 2012). Knowledge of intra-annual dynamics of xylem formation is required to determine seasonal influence of meteorological factors on radial tree growth and evaluate species-specific response to global climate change. Trees (2014) 28:1161–1171 dynamics of wood formation, reports on intra-annual development of xylem and/or phloem tissue in conifers of cold environments are scarce (Alfieri and Evert 1968, 1973; Antonova and Stasova 2006, 2008; Gricar et al 2006, 2007, 2009; Gricar and Cufar 2008). Phloem formation was reported to be less responsive to year-to-year variability of environmental factors compared to xylem formation (Alfieri and Evert 1968; Gricar et al 2007; Gricar and Cufar 2008)
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