Secondary Growth and Carbohydrate Storage Patterns Differ between Sexes in Juniperus thurifera.

Lucía Desoto,José M Olano,Vicente Rozas

doi:10.3389/fpls.2016.00723

Abstract

Differences in reproductive costs between male and female plants have been shown to foster sex-related variability in growth and C-storage patterns. The extent to which differential secondary growth in dioecious trees is associated with changes in stem carbohydrate storage patterns, however, has not been fully assessed. We explored the long-term radial growth and the seasonal variation of non-structural carbohydrate (NSC) content in sapwood of 40 males and 40 females Juniperus thurifera trees at two sites. NSC content was analyzed bimonthly for 1 year, and tree-ring width was measured for the 1931–2010 period. Sex-related differences in secondary growth and carbohydrate storage were site-dependent. Under less restrictive environmental conditions females grew more and stored more non-soluble sugars than males. Our results reinforce that sex-related differences in growth and resource storage may be a consequence of local adaptation to environmental conditions. Seasonal variation in soluble sugars concentration was opposite to cambial activity, with minima seen during periods of maximal secondary growth, and did not differ between the sexes or sites. Trees with higher stem NSC levels at critical periods showed higher radial growth, suggesting a common mechanism irrespective of site or sex. Sex-related patterns of secondary growth were linked to differences in non-soluble sugars content indicating sex-specific strategies of long-term performance.

Highlights

In dioecious plant species, female and male individuals frequently display different performance, i.e., sexual dimorphism, within the same population
We evaluated the variation of non-structural carbohydrate (NSC) contents over a year and radial growth rates during a 80-years period to test the following hypotheses: (1) sapwood NSC content varies between the sexes in terms of concentration and temporal patterns, because male reproductive function mainly occurs at the beginning of the reproductive period, whereas female function extends during the whole reproductive period till fruit ripening (Espírito-Santo et al, 2003; Montesinos et al, 2012b); (2) radial growth rate is lower in female trees, under more limiting conditions (Obeso, 2002; Montesinos et al, 2006; Rozas et al, 2009; Olano et al, 2015); and (3) secondary growth rates are related to hierarchies in stem NSC contents and this relationship is modulated by sex
Non-soluble sugar accounted for a lower portion of NSC than soluble sugars (SS), with an annual mean concentration of 0.8%

Summary

Introduction

Female and male individuals frequently display different performance, i.e., sexual dimorphism, within the same population. Female plants usually allocate proportionally more resources to reproduction leaving less resource available for other functions, such as growth, storage, maintenance or defense, than do males (Nicotra, 1999; Nicotra et al, 2003; Mitchell et al, 2004). In many dioecious woody plants, males exceed females in size, growth rate or survival (Obeso, 2002; Nuñez et al, 2008; Cedro and Iszkułao, 2011). Despite higher reproductive costs, females can display equal or higher growth rates (Rovere et al, 2003) due to compensatory mechanisms (Tozawa et al, 2009) and sexual dimorphism in growth may be not noticeable

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