Genetic variation in foliar carbon isotope composition in relation to tree growth and foliar nitrogen concentration in clones of the F1 hybrid between slash pine and Caribbean pine

The objectives of this study were: (1) to quantify the genetic variation in foliar carbon isotope composition (δ13C) of 122 clones of ca. 4-year-old F1 hybrids between slash pine (Pinus elliottii Engelm var. elliottii) and Caribbean pine (Pinus caribaea var. hondurensis Barr, et Golf.) grown at two field experimental sites with different water and nitrogen availability in southeast Queensland, Australia, in relation to tree growth and foliar nitrogen concentration (Nmass); and (2) to assess the potential of using δ13C measurements, in the foliage materials collected from the clone hedges at nursery and the 4-year-old tree canopies in the field, as an indirect index of tree water use efficiency for selecting elite F1 hybrid pine clones with improved tree growth. There were significant differences in foliar δ13C between the nursery hedges and the 4-year-old tree canopies in the field, between the summer and winter seasons, between the two experimental sites, and between the upper outer and lower outer canopy positions sampled. This indicates that δ13C measurements in the foliage materials are significantly influenced by the sampling techniques and environmental conditions. Significant differences in foliar δ13C, at the upper outer canopy in both field experiments in summer and winter, were detected between the clones, and between the female parents of the clones. Clone means of tree height at age ca. 3 years were positively related to those of the upper outer canopy δ13C at both experimental sites in winter, but only for the wetter site in summer. There were positive, linear relationships between clone means of canopy δ13C and those of canopy Nmass, indicating that canopy photosynthetic capacity might be an important factor regulating the clonal variation in canopy δ13C. Significant correlations were found between clone means of canopy δ13C at both experimental sites in summer and winter, and between those at the upper outer and lower outer canopy positions. Mean clone δ13C for the nursery hedges was only positively related to mean clone stem diameter at 1.3 m height at age 3 years on the wetter site. The clone by site interaction for foliar δ13C at the upper outer canopy was significant only in summer. Overall, the relatively high genetic variance components for foliar δ13C and significant, positive correlations between clone means of foliar δ13C and tree growth have highlighted the potential of using foliar δ13C measurements for assisting in selection of the elite F1 hybrid pine clones with improved tree growth

Morphological and physiological traits influencing biomass productivity in short-rotation coppice poplar

Fast-growing hybrid poplar (Populus spp.) have potential as a short-rotation coppice crop grown for biomass energy. This work identifies traits for fast growth studied in an American interspecific pedigree derived from Populus trichocarpa Torr. & A. Gray × Populus deltoides Marsh. grown in the United Kingdom for the first time. The biomass yield after the first coppice rotation was estimated to range from 0.04 to 23.68 oven-dried t·ha–1·year–1. This great range suggests that genotypes from this pedigree may be used to understand the genetic basis of high yield in short-rotation coppice, which would be advantageous for informing breeding programs for biomass crops. Relationships between stem, leaf, cell traits, and biomass yield were investigated. Partial least-squares analysis was used to order the traits by importance. The traits most influential on biomass were maximum stem height throughout the growing season, basal diameter, number of stems, and number of sylleptic branches, which showed high heritability, indicating excellent potential for breeding programs. The leaf traits, leaf area, number of leaves on the leading stem, and plastochron index were also associated with an increase in biomass, leading to a better understanding of this trait

Genetic variation for carbon isotope composition in Juglans regia L.: relationships with growth, phenology and climate of origin

• Among the traits of breeding interest for the common walnut tree Juglans regia L., characteristics such as timing of budbreak and leaf fall, water-use efficiency and growth performance are regarded as being of utmost relevance in Mediterranean conditions. • The authors evaluated intraspecific variation in $\delta$$^{13}$C (carbon isotope composition, surrogate of intrinsic water-use efficiency, WUE$_{\rm i}$) for 22 J. regia families grown in a progeny test under supplementary irrigation, and investigated whether such variation correlated with climatic indicators of native habitats. The genetic relationships between $\delta$$^{13}$C, growth and phenology were also assessed during two consecutive years. • Overall, the most water-use-efficient families (i.e. with higher $\delta$$^{13}$C), which originated mainly from drought-prone provenance regions which have a high vapour pressure deficit and low rainfall, exhibited less height growth and smaller DBH. Using a stepwise regression procedure, $\delta$$^{13}$C was included as the main explanatory variable of genotypic variation in growth traits, together with growing season duration (for DBH in both years) and flushing (for height in 2007). • It was concluded that WUE$_{\rm i}$ is largely unconnected to phenology effects in the explanation of growth performance for J. regia, therefore suggesting the opportunity of simultaneously selecting for low WUE$_{\rm i}$ and extended growing period to maximise productivity in non-water-limited environments.Variation génétique de la composition isotopique du carbone chez Juglans regia L.: relations avec la croissance, la phénologie et le climat d'origine. • Parmi les traits d'intérêt pour la sélection de noyer commun Juglans regia, des caractéristiques telles que la précocité de débourrement et la date de chute des feuilles, l'efficience d'utilisation de l'eau et la performance de croissance sont considérées comme étant importantes dans les conditions méditerranéennes. • Les auteurs ont évalué la variation intraspécifique de composition isotopique en 13C ($\delta$$^{13}$C, substitut de l'efficience intrinsèque d'utilisation de l'eau, WUE$_{\rm i}$) dans 22 familles de Juglans regia cultivées dans un essai de descendance avec une irrigation d'appoint, et ils ont examiné si la variation était corrélée avec les indicateurs du climat des habitats d'origine. Les relations génétiques entre $\delta$$^{13}$C, croissance et phénologie ont également été évaluées au cours de deux années consécutives. • En général, les familles présentant les plus fortes valeurs de WUE$_{\rm i}$ (c'est-à-dire avec le $\delta$$^{13}$C le plus élevé), qui proviennent essentiellement des régions de provenance à sécheresse élevée et à fort déficit de pression de vapeur et faibles précipitations, présentent une croissance en hauteur moindre et un plus faible diamètre à 1,3 m. En utilisant une procédure de régression par étapes, $\delta$$^{13}$C a été inclus en tant que principale variable explicative de la variation génotypique des caractéristiques de croissance, de concert avec la durée de la saison de croissance (pour le diamètre à 1,3 m) et le débourrement (pour la hauteur en 2007). • Il a été conclu que WUE$_{\rm i}$ est en grande partie sans rapport avec la phénologie dans l'explication de la performance de croissance pour J. regia, suggérant donc la possibilité de sélectionner simultanément pour de faibles niveaux de WUE$_{\rm i}$ et une période de croissance prolongée pour maximiser la productivité dans des environnements où l'eau n'est pas limitante