Mature trees versus seedlings: Differences in leaf traits and gas exchange patterns in three co-occurring Mediterranean oaks

Abstract

-We studied gas-exchange patterns and leaf traits of seedlings and mature trees of three coexisting Mediterranean oaks with contrasting leaf habits (the evergreen Quercus ilex, and the deciduous Q. faginea and Q. pyrenaica) during the well-watered part of the growth season. Leaf life span in Q. ilex seedlings was shorter than in mature trees, whereas for the deciduous species the differences in leaf life span between both growth stages were less pronounced. In all species leaves on seedlings displayed a lower mass per unit area and lower nitrogen content than on mature trees. However, owing to their larger stomatal conductance, leaves on seedlings usually showed larger photosynthetic nitrogen-use efficiency and lower water-use efficiency than on mature trees. Stomatal conductance and CO 2 assimilation rate were lower in Q. ilex than in the two deciduous species at the mature stage. However, the interspecific differences in gas exchange rates related to differences in leaf longevity disappeared at the seedling stage because in Q. ilex the seedlings showed a much higher stomatal conductance than the adults. Thus, seedlings of the three species showed a common strategy, regardless of the leaf life span, probably as a response to the competition from the herbaceous layer.growth stages / leaf gas-exchange / leaf traits / Quercus sp.Résumé -Arbres adultes versus semis : différences de caractéristiques foliaires des types d'échanges gazeux chez trois espèces coexistantes de Quercus. Les échanges gazeux et les caractéristiques foliaires des semis et des arbres adultes de trois espèces coexistantes de chênes méditerranéens présentant des caractéristiques foliaires contrastées (une espèce à feuille persistante Quercus ilex et deux espèces à feuille caduque Q. faginea et Q. pyrenaica) ont été étudiés lors des phases les plus favorables de la saison de croissance. La longévité foliaire des semis a été inférieure à celle des adultes pour Q. ilex et similaire pour les deux autres espèces. Les feuilles des semis ont un poids plus faible par unité de surface et une moindre teneur en azote que celle des adultes. Cependant, à cause de leur plus forte conductance stomatique, les semis ont montré une meilleure efficience d'utilisation de l'azote dans la photosynthèse et une plus faible efficience d'utilisation de l'eau que les arbres adultes. La conductance stomatique et l'assimilation de CO 2 ont été plus faibles pour Q. ilex par rapport aux deux autres espèces à l'état adulte. Cependant, les différences interspécifiques dans les échanges gazeux ont disparu au stade semis, et les semis de Q. ilex ont présenté une conductance stomatique beaucoup plus forte que les arbres adultes. Les plantules de trois espèces ont donc présenté une stratégie commune, indépendamment de leur longévité foliaire, vraisemblablement en réponse à la concurrence de la strate herbacée. stades de croissance / échanges gazeux foliaires / caractéristiques foliaires / Quercus sp.

Short-term responses of Picea asperata seedlings of different ages grown in two contrasting forest ecosystems to experimental warming

“…Many aspects of leaf morphology and physiology may vary with tree age (Thomas and Winner, 2002;Mediavilla and Escudero, 2003). Furthermore, most previous studies have demonstrated that juvenile age classes are likely to be more sensitive to environmental stress (e.g., temperature and moisture) than mature trees (Howe et al, 2004;Greenwood et al, 2008), with less research focusing on the ecophysiological performances of younger, and smaller life stages.…”

“…This was probably because very young seedlings generally lack fully expanded lateral branches and may devote more assimilation to new needle growth (Kohyama, 1983). Comparative studies of different growth stages may provide essential information for understanding the strategies adopted by the species at different stages of their life cycle, as well as the selective pressures that operate in each stage (Mediavilla and Escudero, 2003). In this case, there were clear differences in photosynthetic performances (e.g., LCP, AQY and g s ) between two age classes.…”

“…Furthermore, many previous studies have demonstrated that juvenile age trees may be more sensitive to environmental changes (i.e., temperature, moisture) than mature trees (Howe et al, 2004;Greenwood et al, 2008), with less research focusing on the ecophysiological performances of younger, and smaller life stages (Reinhardt et al, 2009). Comparative studies of different growth stages may provide essential information for understanding the strategies adopted by the species at different stages of their life cycle, as well as the selective pressures that operate in each stage (Mediavilla and Escudero, 2003). To our knowledge, to date, little is known about warming effects on the morphological and physiological performances of the trees with different life stages.…”

Does ontogeny modulate irradiance-elicited plasticity of leaf traits in saplings of rain-forest tree species? A test with Dicorynia guianensis and Tachigali melinonii (Fabaceae, Caesalpinioideae)

“…It is now well established that leaf and whole plant traits change with tree size (mainly height) and age (e.g. Hoflacher and Bauer, 1982;Mediavilla and Escudero, 2003;Rijkers et al, 2000;Thomas and Winner, 2002). Tree height is known to influence structural and physiological leaf traits possibly due to hydraulic constraints imposed by increased transport distance (Niinemets, 1997a;2002;Rijkers et al, 2000).…”

The relevance of seed size in modulating leaf physiology and early plant performance in two tree species

“…One interpretation of the above result is that low WUE was advantageous for plants. An efficient use of water may help plants to survive persistent droughts in arid environments but be disadvantageous in seasonally dry and competitive habitats (Ehleringer 1993;Mediavilla and Escudero 2003;Nicotra and Davidson 2010;Picotte et al 2007;Sandquist and Ehleringer 2003). Alternatively, assuming that first-year leaf 5 C resulted from the seed-toleaf mobilization of C-enriched components, the increasing probability of survival of Q. pyrenaica as leaf 5 C decreased could be mostly reflecting a positive effect of first-year photosynthetic carbon gain on subsequent survival.…”