Acorn production is linked to secondary growth but not to declining carbohydrate concentrations in current-year shoots of two oak species |
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Authors: | Arben Q Alla J Julio Camarero Melchor Maestro-Martínez Gabriel Montserrat-Martí |
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Institution: | 1.Instituto Pirenaico de Ecología (CSIC),Zaragoza,Spain;2.ARAID-Instituto Pirenaico de Ecología (CSIC),Zaragoza,Spain |
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Abstract: | In trees, reproduction constitutes an important resource investment which may compete with growth for resources. However,
detailed analyses on how growth and fruit production interact at the shoot level are scarce. Primary canopy growth depends
on the development of current-year shoots and their secondary growth might also influence the number and size of fruits supported
by them. We hypothesise that an enhanced thickening of current-year shoots is linked positively to acorn production in oaks.
We analysed the effect of acorn production on shoot growth of two co-occurring Mediterranean oak species with contrasting
leaf habit (Quercus ilex, Quercus faginea). Length and cross-sectional area of current-year shoots, apical bud mass, number of leaves and acorns, xylem and conductive
area, number of vessels of acorn-bearing and non-bearing shoots were measured in summer and autumn. Nitrogen and carbohydrates
analyses were also performed in stems and leaves of both shoot types. Stem cross-sectional area increased in acorn-bearing
shoots when compared with non-bearing shoots for both species and such surplus secondary growth was observed since summer.
In bearing shoots, the total transversal area occupied by vessels decreased significantly from basal to apical positions along
the stem as did the xylem area and the number of vessels. Leaves of bearing shoots showed lower nitrogen concentration than
those of non-bearing shoots. Carbohydrate concentrations did not differ in stems and leaves as a function of the presence
of acorns. Such results suggest that carbohydrates may preferentially be allocated towards reproductive shoots, possibly through
enhanced secondary growth, satisfying all their carbon demands for growth and reproduction. Our findings indicate that acorn
production in the two studied oaks depends on shoot secondary growth. |
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