Marina Stecconi

Annual shoot-growth in Nothofagus antarctica (G. Forster) Oersted (Nothofagaceae) from northern Patagonia

Abstract The growth dynamics of annual shoots of Nothofagus antarctica shrubs from northern Patagonia was studied. The pattern of extension of the shoots derived from the three most distal buds of 100 parent shoots was registered. Weekly measurements and observations of extending shoots were carried out during the 1996–1997 growth season. The date of shoot extension initiation was less variable than the date of shoot extension cessation. Extension curves had an asymmetrically sigmoid outline. Most extension took place uninterruptedly between mid-September 1996 and the end of January 1997. Extension rate reached its highest value in the second half of the extension period. Leaf unfolding rate had a peak early in the extension period and fluctuated irregularly later on. The apical meristem of all shoots died by the end of shoot extension. In general terms, shoot length, diameter, leaf number and extension duration decreased from the first to the third position from the parent shoot’s apex, although exceptions to this pattern were found. Shoot extension rate was affected by maximum and minimum daily temperatures but not by the amount of precipitation during the extension period. The size of a bud was not related to the size of the shoot derived from it. The size of shoots in the third position from the apex was related to parent shoot size; this was not the case for more distal shoots.

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...

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.

Desarrollo temprano del roble (Nothofagus obliqua): un análisis arquitectural de procedencias de Argentina

Se estudio el desarrollo arquitectural en tres anos de plantulas de Nothofagus obliqua bajo condiciones de vivero. Las plantulas derivaron de semillas de cinco procedencias dentro del area de distribucion natural de esta especie en Argentina. En no menos de 40 plantas por procedencia se registraron: longitud, numero de nudos y diametro basal de los brotes anuales del eje vertical principal. El brote del primer ano de todas las plantulas consistio en una sola unidad de alargamiento (UA), el del segundo ano en una o dos UA y el del tercero en una, dos o tres UA. El desarrollo de dos o tres UA resulto invariablemente de la muerte del meristema apical luego de la primera UA. Las consecuencias mas evidentes de la existencia de mas de un evento de alargamiento en un ano fueron: (a) mayores longitud y numero de nudos en ese ano, (b) mayor engrosamiento del tronco al nivel del suelo y (c) un periodo de alargamiento mas largo. Plantas de diferente procedencia difirieron en la longitud del brote del primer ano y en las proporciones de brotes de los anos siguientes con una o varias UA.

Testing individual inter-annual variations in flower production by means of retrospective analysis of meristem allocation in two tree species

High inter-annual variations in flower and seed production have been frequently reported for wind-pollinated tree species. Such variations have been generally studied from a population perspective. The present study focuses on the meristematic cost of flower production in main branches of Nothofagus obliqua and N. nervosa through a retrospective analysis of flower production over 4–5 consecutive years. In both species, the percentage of flowering nodes in one year varied between 0 and 55 %. In N. obliqua, total flower production was bimodally distributed: years of high and low production were more common than years of intermediate production. Bimodality was not significant either for total flower production in N. nervosa or for each flower type separately in both species. Flower production affected branching negatively, which meant a meristematic cost. Periodicity in flower production was uneven among co-specific trees; more than two consecutive years of high flower production were rare in all trees. Inter-annual variations in the production of staminate and pistillate flowers were synchronized. In N. nervosa, the production of pistillate flowers tended to be more variable among years than the production of staminate flowers. The applied technique helps in the assessment of individual variations of flower production and contributes to understanding factors promoting seed-production variations in tree species at population scale.

Morpho-physiological responses of Nothofagus obliqua to light intensity and water status, with focus on primary growth dynamics

Key messageIntra-individual variations of plant responses to environmental conditions are related to axis differentiation. Plastic responses include variations in primary growth, shoot allometry, leaves’ chlorophyll content and water use efficiency.AbstractPrimary growth affects plant plasticity by influencing the number, spatial arrangement and time of differentiation of the leaves. For Nothofagus obliqua, we evaluated if primary shoot growth dynamics determines short-term responses to environmental conditions, and intra-individual variations in such responses. Before bud-break, saplings were located in experimental conditions, combining two light treatments with two water supply treatments. For each individual, morphology, relative extension rate (RER), and relative leaf chlorophyll content (SPAD units) were registered for the annual shoot derived from the most distal bud of two axis categories: the main axis (trunk) and a main branch. For trunk shoots, we analysed the net photosynthetic rate at saturating photosynthetic photon flux density (Psat) of proximal and distal leaves. Shaded trees had higher RER, longer and more slender shoots, longer internodes, and higher leaf chlorophyll content than unshaded trees. The number of nodes was affected by water condition in trunk shoots, and by light condition in main branch shoots. Full sunlight stimulated the development of a branch following the length and growth direction of its parent shoot (relay branch). Shade would have promoted the development of neoformed leaves. Under shade and low water availability, water use efficiency was higher in distal than proximal leaves. Under high sunlight and water availability, leaves of relay branches presented slightly higher Psat with higher water loss than both proximal preformed leaves and distal leaves under the other tested conditions. This study highlights the need of assessing intra-individual variations in shoot acclimation in relation to axis differentiation.