The relative weight of ontogeny, topology and climate in the architectural development of three North American conifers

International audienceKnowledge of plant architecture allows retrospective study of plant development, hence provides powerful tools, through modelling and simulation, to link this development with environmental constraints, and then predict its response to global change. The present study aims to determine some of the main endogenous and exogenous variables driving the architectural development of three North American conifers. We measured architectural traits retrospectively on the trunk, branches and twigs of whole tree crowns for each species: annual shoot length (ASL), needle length, branching patterns and reproduction organs (male and female). We fitted a partial least square (PLS) regression to explain each architectural trait with respect to topological, ontogenic and climatic variables. Results showed a significant weight of these three groups of variables for previous and current year, corresponding, respectively, to organogenesis and elongation. Topological and ontogenic variables had the greatest weight in models. Particularly, all architectural traits were strongly correlated with ASL. We highlighted a negative architectural response of two species to higher than average temperatures, whereas the third one took advantage of these higher temperatures to some degree. Tree architectural development weekly but significantly improved with higher precipitation. Our study underlines the strong weight of topology and ontogeny in tree growth patterns at twig and branch scales. The correlation between ASL and other tree architectural traits should be integrated into architectural development models. Climate variables are secondary in importance at the twig scale. However, interannual climate variations influence all axis categories and branching orders and therefore significantly impact crown development as a whole. This latter impact may increase with climate change, especially as climate affects architectural traits over at least 2 years, through organogenesis and elongation

Growth phenology in Pinus halepensis Mill.: apical shoot bud content and shoot elongation

International audienceContext : Analysis of annual shoot length growth phenology is crucial to assess the impact of climate change on tree production. Little is known about the basic growth characteristics and the phenology of pines.Aims: The present study disentangles the roles of shoot organogenesis vs elongation in the annual growth cycle of the polycyclic Aleppo pine.Methods: Growth of young Pinus halepensis trees was monitored monthly for 1 year. At each monitoring date, the bud content and meristem dimensions of the main stem shoots apices were analyzed.Results: The two first growth units of an annual shoot are preformed inside the bud during the previous year. The following growth units are formed during the spring or summer of the current year. The gap between a shoot organogenesis and its elongation may vary from 1 month, for the last growth unit, to half a year, for the first growth units.Conclusion: Our results underline the importance of taking seasonal environmental conditions from both the previous and the current year into account, in order to study the plasticity of annual shoot growth and its response to climate change and variability

Pith: A new criterion for monitoring the architecture in Mediterranean pines

Plant architecture can be used to study plant development retrospectively thanks to time-dependent morphological markers, particularly those corresponding to the winter break in temperate regions. The Aleppo Pine and the Turkish Pine are polycyclic species, thus they usually develop several consecutive growth units per year, making it sometimes difficult to date them. In this study, we show that keeping track of the pith diameter profile, to date each shoot, is an efficient method. The pith diameter is larger on the first growth unit than on the last growth unit of the year. Moreover, a pairwise comparison showed that the pith diameter undergoes a decrease along the annual shoot from the first growth unit to the last. As pith diameter decreases upwards the annual shoot, it can be used for dating. Pith diameter progresses from 1 year to another too: there is an increase in the early years of life, corresponding to the tree's establishment phase. Lastly, we found a positive relationship between the basal pith diameter of an annual shoot and its length. The variability around this relationship could reflect environmental conditions, especially climate conditions. (Résumé d'auteur