Difference in cuticular transpiration and sclerophylly in juvenile and adult pine needles relates to the species-specific rates of development

Abstract

Pinus species show remarkable ontogenetic differences in needle morphology (heterophylly) between juvenile and adult vegetative phases. This developmental shift may play an adaptative role in their success under diverse habitats. As a first step to know the functional differences between each vegetative phase, we compared water loss through the cuticles of juvenile and adult needles of 21-month-old nursery-grown seedlings of nine hard pine species. Cuticular transpiration (CT), calculated after complete stomatal closure, was obtained by leaf-drying curves, and was related to leaf, ontogenetic and climatic parameters. The rate of cuticular transpiration (RCT) between juvenile and adult needles differed across pine species, and in particular segregated the Mediterranean species Pinus canariensis and P. halepensis, from the Eurasian P. uncinata and introduced species P. radiata. For these species, RCT was always higher in juvenile needles. The different leaf and ontogenic parameters studied were correlated with the variation in RCT among the nine pine species. We discuss this relationship in the light of the species ecology. Besides their possible adaptive interpretation, these results suggest an underlying need to consider the ontogenetic heterophylly when assessing functional traits in hard pine seedlings, in particular those traits that govern water relations.

Biomass allocation and foliage heteroblasty in hard pine species respond differentially to reduction in rooting volume

“…The divergent reaction norms for ontogenetic heteroblasty among pines can have an adaptive significance that merits further investigation, especially considering that secondary needles are more frost and drought-tolerant than primary needles Pardos et al 2009). Our results are also relevant from a practical point of view because they provide a functional basis for choosing the optimum container size for the production of high-quality plants for Mediterranean Europe (Aphalo and Rikala 2003;Dominguez-Lerena et al 2006).…”

Ontogenetic differentiation between Mediterranean and Eurasian pines (sect. Pinus) at the seedling stage

“…Primary and secondary needles have significantly different specific leaf area Pardos et al 2009) thus the relative amount of each foliage type associated to the particular stage of development at the time of harvest affected leaf area traits in a very complex way. Therefore, we intentionally discarded leaf area-related traits for the purposes of this experiment.…”

“…Previous research Fig. 1 Different ontogenetic changes in hard pines: a first appearance of secondary needles in dwarf shoots in Pinus pinaster b profuse axillary long (juvenile) shoots in P. halepensis c juvenile apical rosette during winter in P. radiata d first true winter buds in P. brutia has shown species-specific differences in cuticular transpiration and frost tolerance between primary and secondary needles of this group of species, suggesting an adaptive role of the heterophylly associated to the heteroblastic change Pardos et al 2009) Our main objective was to test the hypothesis that Mediterranean and Eurasian hard pines form two distinct groups based on their ontogenetic heteroblasty. As a secondary objective we wanted to unveil how different developmental features linked to seedling ontogeny integrate with plant allometry.…”

Freezing injury in primary and secondary needles of Mediterranean pine species of contrasting ecological niches

“…The ontogeny of the eight studied species varied greatly from the much delayed Mediterranean species (especially P. canariensis, P. pinea and P. halepensis) to the much faster Eurosiberian species (Pardos et al, 2008). We therefore chose an strategic seedling age, 18 months, such that most species had developed dwarf shoots with secondary needles in the axils of primary needles (transitional vegetative metamers) while juvenile needles were still healthy (Fig.…”

“…Conversely, Eurosiberian pines such as P. sylvestris show a much faster ontogeny with secondary needles forming at the end of the first vegetative period and a subsequent senescence of primary needles. Secondary needles have been shown to have significantly lower specific leaf area (hence higher sclerophylly) than primary needles (Climent et al, 2006;Pardos et al, 2008). Since sclerophylly may provide resistance to frost damage delaying the propagation of ice in tissues with densely lignified or cutinized barriers (Larcher, 2005), it is worth to know if different levels of freezing injury between primary and secondary pine needles can be partly explained by their different degree of sclerophylly.…”