Daniel Barthélémy

Ontogenetic trends in the morphological features of main stem annual shoots of Pinus pinaster (Pinaceae)

Phase change refers to the transition between juvenile and adult vegetative phases. The study of trees throughout their entire life span requires retrospective analyses and validates the use of a chronosequence by sequencing observations at different and successive stages. The main axis growth pattern of 62 maritime pines (Pinus pinaster) selected in a chronosequence of three stands consisting of 8-, 22-, and 48-yr-old trees was analyzed retrospectively. Comparison of measured features (length, number of axillary products, reproductive organs) at common ages from the three stands supported the validity of using these data to form a continuous chronosequence. Endogenous trends in tree development are revealed free from variability due to annual growth conditions. Two main phases of development corresponding respectively to the juvenile vegetative and adult reproductive stages were identified, and the transition between both occurred in 9-yr-old trees. The relevance of these two phases and more generally the notion of phase changes are discussed in light of observed trends in the values of studied growth and branching parameters that may either show gradual variations (such as length of annual shoot) or a distinctive expression in one or the other phase (such as presence of female cones).

The plant-ant Camponotus schmitzi helps its carnivorous host-plant Nepenthes bicalcarata to catch its prey

The Bornean climber, Nepenthes bicalcarata , is unique among plants because it is both carnivorous and myrmecophytic, bearing pitcher-shaped leaves and the ant Camponotus schmitzi within tendrils. We explored, in the peat swamp forests of Brunei, the hypothesis that these ants contribute to plant nutrition by catching and digesting its prey. We first tested whether ants increased plants capture rate. We found that unlike most plant-ants, C. schmitzi do not exhibit dissuasive leaf-patrolling behaviour (zero patrol on 67 pitchers of 10 plants) but lie concealed under pitcher rim (13 ± 6 ants per pitcher) allowing numerous insect visits. However, 47 out of 50 individuals of the largest visitor dropped into the pitchers of five plants were attacked by ants and the capture rate of the same pitchers deprived of their ambush hunting ants decreased three-fold. We then tested whether ants participated in plants digestion. We showed in a 15-d long experiment that ants fed on prey and returned it in pieces in seven out of eight pitchers. The 40 prey deposited in ant-deprived pitchers remained intact indicating a weak digestive power of the fluid confirmed to be only weakly acidic (pH ~5, n = 67). The analysis of 10 pitcher contents revealed that prey, mainly ants and termites, was very numerous (~400 per pitcher per plant) and highly fragmented. Altogether, these data suggest a positive effect of C. schmitzi on both prey intake and breakdown. This ant–plant interaction could thus be a nutritional mutualism involving the unusual association of carnivory and myrmecotrophy.

Synchronization of growth, branching and flowering processes in the South American tropical tree Cecropia obtusa (Cecropiaceae)

Cecropia obtusa Trécul (Cecropiaceae) is a pioneer species associated with the initial phases of regeneration of tropical South American forests. A comparison of the succession of morphological events associated with each node (inflorescences or branches developed or aborted and underlying internode length) making up the axes of 30 trees helped to establish a link between their architecture and the regularity and synchronicity of their expression of growth, flowering, and branching processes over time on an individual and stand level. For a given individual, new nodes are emitted at the same rate on all the axes, irrespective of their branching order. Flowering and branching alternate, and these processes occur in all the axes of the tree synchronously. On a stand level, flowering and branching occur regularly every 35 nodes or so, which apparently corresponds to an annual rhythm. Under nonlimiting conditions, a single branch tier would be emitted each year, and it is thus possible to determine a posteriori the age of a crown accurately. The merits of the method, the possibility of estimating the age of natural Cecropia obtusa regrowth by observing tree architecture, and the possible applications in the field of ecology are discussed.

An architectural approach to the growth forms of Nothofagus pumilio (Nothofagaceae) along an altitudinal gradient

Variations in the architecture and axis structure of different growth forms of Nothofagus pumilio (Poepp. et Endl.) Krasser (Nothofagaceae) were studied along an altitudinal gradient. We evaluated the primary growth and branching pattern of annual shoots belonging to the main axis categories (trunk, main branches, and secondary (short) branches) of four growth forms developed at different altitudes (1200–1600 m a.s.l.) in northern Patagonia: (i) low shrubs at the high-altitude timberline, (ii) high shrubs at high altitude, (iii) low trees at mid-altitude slopes, and (iv) high trees at low-altitude single-species forests. Shoot structure and branch distribution along shoots were similar for all axis categories and growth forms. Significant differences between axis categories were found regarding the sizes of shoots, which decreased from trunk to secondary/short branches. For each axis category, shoots of similar size differed between growth forms in stem slenderness and internode length. The extent of diff...

Retrospective analysis of tree architecture in silver fir (Abies alba Mill.): ontogenetic trends and responses to environmental variability

ContextUnderstanding the effects of exogenous factors on tree development is of major importance in the current context of global change. Assessing the structure development of trees is difficult given that they are large and complex organisms with lifespan of several decades.AimsWe used a retrospective analysis to derive the ontogenetic trends in silver fir development and assess the effects of climate or light environment on tree architecture.MethodsThanks to the identification of relevant growth markers (bud cataphylls and pseudo-whorl branches), a retrospective analysis allowed to record annual shoot extension and to date them on silver firs of various sizes under different environmental conditions.ResultsThe length of successive annual shoots located on different axes clearly show gradual trends related to the physiological age of meristems. Within- and between-tree variations are noted due to the plasticity of development and growth induced by light environment and climate.ConclusionRetrospective analysis is an efficient method for getting information on the history of trees architecture and subsequently to relate it to environmental factors.

Morphological trends in main stem of Pinus radiata D. Don: Transition between vegetative and reproductive phase

Abstract Developmental patterns of structural units of the main tree axis of Pinus radiata were investigated in two plantations in Chile growing under different ecological conditions. Environmental characteristics of sites were recorded and structural features of sample trees were measured. Annual shoot length, number of growth units per annual shoot, growth unit length, and number of branches and cones per growth unit were statistically compared between sites and between vegetative and reproductive phases of trees. No clear pattern of stand development was apparent when variables were directly examined in terms of actual dimensions (cm) and time scale (years). In contrast, common patterns of development of structural parameters were indicated after dimensions and time were normalized so as to express them on a ontogenetic scale. The number of growth units per annual shoot and average length of annual shoot increased during the juvenile stage of development. Transition from juvenile to mature stages brought about a change in this trend, either stabilizing or reversing the pattern of development and size of these structural elements. The practical consequence of these changes on wood quality for industrial purposes is discussed.

Shoot development and dieback in progenies of Nothofagus obliqua

Shoot growth and dieback were compared among progenies of nursery-grown seedlings of Nothofagus obliqua belonging to seven progenies of the same provenance (Quila-Quina, Argentina). First-year shoots consisted of one growth unit (GU) and second-year shoots of one or two GUs. The probability of development of two GU was similar for all progenies. Progenies were different in terms of shoot size, terminal bud abscission, the extent of shoot dieback after shoot extension and the node of origin of the relay shoot on the first shoot. Plants with a second-year shoot consisting of two GUs had a thicker stem and more nodes than those with single-GU shoots. The selection of N. obliqua seed trees based on architectural traits suitable for forestry development at specific sites must contemplate variability among progenies and their probabilities of successful development under different conditions.RésuméLa croissance et le dépérissement des pousses ont été comparés entre sept descendances de Nothofagus obliqua élevées en pépinière et issues d’une même provenance (Quila-Quina, Argentine). Les pousses de la première année n’étaient formées que d’une seule Unité de Croissance (UC) tandis que les pousses de deuxième année étaient constituées d’une ou deux UCs. La probabilité de développement d’une deuxième UC était constante quelle que soit la descendance. Les descendances ont montré des différences en termes de taille de pousse, d’abscission du bourgeon terminal, d’étendue de dépérissement des UC en fin d’extension et vis-à-vis du nœud d’origine de la pousse relais sur la pousse de première année. Les plantes avec une pousse de seconde année comportant deux UC avaient une tige plus épaisse et avec plus de nœuds que celles avec des pousses à une seule UC. La sélection, basée sur des traits architecturaux, d’arbres de N. obliqua issus de graines, pour qu’elle soit adaptée à la foresterie, doit prendre en compte la variabilité entre descendances et leurs probabilités de réussite et de bon développement sous des conditions diverses.