Intra-annual wood density fluctuations and tree-ring width patterns are sex- and site-dependent in the dioecious conifer
Juniperus thurifera L.
Jose´ Miguel Olano1 • A. I. Garcı´a-Cervigo´n1 • A. Arzac2 • V. Rozas3
Received: 9 January 2015 / Revised: 10 April 2015 / Accepted: 27 April 2015 Springer-Verlag Berlin Heidelberg 2015
Key message Sex and site conditions modulate intraand inter-annual secondary growth and its climatic sensitivity in a dioecious Mediterranean conifer.
Abstract Divergent evolutionary pressures associated with differential reproductive costs in dioecious trees may lead to sex-related variation in non-reproductive functions.
Sex-related differences may be site-dependent, with different outcomes depending on environmental conditions.
We explored the effects of sex and environmental conditions on the climatic control of annual secondary growth and intra-annual wood density fluctuations (IADF) of a dioecious conifer (Juniperus thurifera L.) growing in two sites with contrasting hydrological conditions under a continental Mediterranean climate. Different sex-related strategies had variable effects on relative secondary growth, with females outperforming males under more favorable hydrological conditions, and males outperforming females under water-limited conditions. Ring width and
IADF formation were driven by climatic factors occurring at different temporal scales. Tree-ring growth depended on factors acting prior to the initiation of the xylogenesis and to conditions directly affecting the duration and pace of cambial activity, and ring width, therefore, integrated a complex signal of factors occurring over a relatively long period, and on an annual cycle. In contrast, IADFs responded to singular short-term events that alleviated drought and promoted cambial reactivation during the summer arrest. Female trees showed a more opportunistic water use, displayed in the stronger ring-width response to
June–July conditions. Enhanced cambial sensitivity in females set a lower threshold for IADF occurrence, leading to a higher frequency of IADFs irrespective of site. Intraannual and inter-annual female growth patterns reflect an opportunistic strategy to benefit from favorable climatic windows.
Keywords Dendroecology Dioecy IADF Juniperus thurifera Mediterranean climate
In dioecious plants, males and females face contrasting selective pressures due to disparity in the magnitude and timing of their investment of resources in reproduction (Obeso 2002). As a result, plant performance may vary between the sexes with differences in growth rates (Obeso 2002; Hultine et al. 2008; Cedro and Iszkuło 2011), carbon allocation patterns (Vilas and Pannell 2011; L. DeSoto unpubl. data) or investment in defensive compounds (Cornelissen and Stiling 2005; Graff et al. 2013). Eventually, these differences may lead to distinct mortality rates (Allen and Antos 1993; El Mujtar et al. 2012) and so biased sex ratios (Graff et al. 2013). However, divergent evolutionary pressures may cause sex-related variation in nonCommunicated by Y. Sano. & Jose´ Miguel Olano email@example.com 1 A´rea de Bota´nica, Departamento de Ciencias Agroforestales,
EU de Ingenierı´as Agrarias, Universidad de Valladolid,
Campus Duques de Soria, 42004 Soria, Spain 2 Departamento de Biologı´a Vegetal y Ecologı´a, Facultad de
Ciencia y Tecnologı´a, Universidad del Paı´s Vasco, Barrio
Sarriena s/n, 48940 Leioa, Spain 3 Misio´n Biolo´gica de Galicia, Consejo Superior de
Investigaciones Cientı´ficas, Apdo. 28, 36080 Pontevedra,
DOI 10.1007/s00468-015-1212-5 reproductive structures, modifying plant functions such as water use efficiency, photosynthetic activity or nutrient acquisition (Hultine et al. 2008; Montesinos et al. 2012a).
Such sex-dependent functional changes may lead to compensatory effects that reduce the differences in performance that would arise from differences in reproductive costs alone.
Resource assignment to secondary growth is a low priority compared to other plant functions. As a result, changes in secondary growth are good proxies of the whole plant performance (Hughes et al. 2011). In many perennial plants, investment in xylem secondary growth across their whole lives can be easily evaluated through the study of ring-width time series (Babst et al. 2014). Dendrochronological studies on dioecious trees have found that males reach higher growth rates than females just after achievement of the reproductive stage (Ban˜uelos and Obeso 2004; Montesinos et al. 2006; Iszkulo and Boratynski 2011). However, other studies have found higher growth rates in females, in spite of their higher reproductive costs, supporting the existence of compensatory mechanisms (Dawson and Ehleringer 1993; Rozas et al. 2009). In fact, the relative performance of male and female plants may vary depending on local environmental conditions (Iszkuło et al. 2011; Hultine et al. 2013). This indicates that the negative influence of higher reproductive effort on the amount of resources available for vegetative growth may be modulated by the environment.
For instance, the relative performance of males and females is sensitive to water availability, due to the lower water use efficiency and higher stomatic transpiration described for females in comparison to males (Xu et al. 2008; Montesinos et al. 2012a; Hultine et al. 2013). This diverging functionality has been reflected in contrasting sex-specific responses of secondary growth to climate, usually with greater sensitivity to drought conditions for females than for males (Rozas et al. 2009; Cedro and Iszkuło 2011).
Annual rings are particularly easy to identify in most conifers due to the existence of two contrasting tracheid types formed in different seasons. At the beginning of the growing season, tracheids present higher lumen-to-wall ratios than at the end of that period, leading to clear and dark bands representing earlywood and latewood, respectively. This annual pattern of clear/dark bands may be disrupted by the occurrence of bands of tracheids with unusually low/high lumen-to-wall ratios immersed in the earlywood/latewood (Young et al. 1993; Wimmer et al. 2000), leading to two or more ring-like structures within each annual ring, called false rings or intra-annual density fluctuations (IADF). IADF formation can be triggered by multiple environmental cues including insect outbreaks (Priya and Bhat 1997), pollution (Kurczynska et al. 1997), flooding (Young et al. 1993) or climate (De Luis et al. 2011). Climatic factors triggering IADF formation are complex and highly idiosyncratic, but as a general rule,