Javier Puntieri

Interannual variations in primary and secondary growth of Nothofagus pumilio and their relationships with climate

Key messageThe aim of this study is to evaluate the relationships between primary and secondary growth as well as the influences of climate variations on both types of growth.AbstractThe relationships between apical (or primary) and radial (or secondary) growth, and climatic influences on both types of growth, were evaluated for Nothofagus pumilio (Nothofagaceae), the dominant subalpine tree in Patagonia. We measured the spacing and number of nodes of annual shoots developed in the period 2001–2010 in 40 N. pumilio trees growing near the upper treeline in the northern Patagonian Andes (41°S). Variations in ring width at the base of each trunk were also recorded. Interannual variations in primary and secondary growth were significantly related to each other, and to several climate variables. Mean temperatures in winter and early spring (June–October) prior to the period of shoot extension were positively associated with both primary and secondary growth. In addition, total summer precipitation (December–March) was positively related to shoot extension, whereas mean summer temperature during the previous growth season (January–March) was directly related to radial growth. These climatic influences on N. pumilio growth may play a major role in regulating the expressions of preformation and neoformation.

Preformation and distribution of staminate and pistillate flowers in growth units of Nothofagus alpina and N. obliqua (Nothofagaceae)

BACKGROUND AND AIMSnThe distribution and differentiation times of flowers in monoecious wind-pollinated plants are fundamental for the understanding of their mating patterns and evolution. Two closely related South American Nothofagus species were compared with regard to the differentiation times and positions of staminate and pistillate flowers along their parent growth units (GUs) by quantitative means.nnnMETHODSnTwo samples of GUs that had extended in the 2004-2005 growing season were taken in 2005 and 2006 from trees in the Lanín National Park, Patagonia, Argentina. For the first sample, axillary buds of the parent GUs were dissected and the leaf, bud and flower primordia of these buds were identified. The second sample included all branches derived from the parent GUs in the 2005-2006 growing season.nnnKEY RESULTSnBoth species developed flowering GUs with staminate and/or pistillate flowers; GUs with both flower types were the most common. The position of staminate flowers along GUs was similar between species and close to the proximal end of the GUs. Pistillate flowers were developed more distally along the GUs in N. alpina than in N. obliqua. In N. alpina, the nodes bearing staminate and pistillate flowers were separated by one to several nodes with axillary buds, something not observed in N. obliqua. Markovian models supported this between-species difference. Flowering GUs, including all of their leaves and flowers were entirely preformed in the winter buds.nnnCONCLUSIONSnStaminate and pistillate flowers of N. alpina and N. obliqua are differentiated at precise locations on GUs in the growing season preceding that of their antheses. The differences between N. alpina and N. obliqua (and other South American Nothofagus species) regarding flower distribution might relate to the time of anthesis of each flower type and, in turn, to the probabilities of self-pollination at the GU level.

Genetic variation in architectural seedling traits of Patagonian cypress natural populations from the extremes of a precipitation range

Abstract• Species distributed along wide environmental ranges are expected to be either plastic or adapted to local optima. The elucidation of which of these alternatives prevails, is crucial in planning breeding and conservation strategies for not yet domesticated species. Austrocedrus chilensis (Cupressaceae) is the most commercially important conifer of the temperate forests of Argentina and the target of a domestication program. A steep precipitation gradient characterizes its Argentinean range.• Variation within and differentiation among four natural populations of this Patagonian cypress representative of two contrasting precipitation regimes (>1 300 and 330 mm per y) were assessed by analyzing several morpho/architectural traits in one-year-old seedlings grown in a greenhouse.• Progenies from one of the two xeric populations did not differ from those corresponding to both humid-site populations. The two most variable populations in terms of additive genetic variance belonged to contrasting precipitation regimes. Differentiation among populations was low as measured by each and every variable (average Qst = 0.088). Morphological traits related to the main axis size would have a dubious adaptive meaning.• The results suggest that the Patagonian cypress would have not evolved genetic pools adapted to local optima, and thus it appears to be a phenotypically plastic species, at least regarding growth at juvenile age.Résumé• Les espèces presentant de vastes aires de répartition avec des fortes variations de l’environnement sont soit plastiques, soit adaptées à des optima locaux. Identifier laquelle de ces deux alternatives est celle qui prévaut est une étape cruciale pour planifier des stratégies d’amélioration génétique ou de conservation d’espèces non encore domestiquées. Austrocedrus chilensis (Cupressaceae) est le conifère le plus important du point de vue commercial dans les forêts tempérées d’Argentine et fait l’object d’un programme de domestication. Un fort gradient de précipitations caractérise son aire de répartition en Argentine.• Les variations intra-population et la différenciation entre quatre populations naturelles représentatives de deux régimes contrastés de précipitations (>1 300 mm et 330 mm par an) ont été évaluées en analysant plusieurs traits d’architecture et de morphologie sur des plants âgés de un an cultivés sous serre.• Les descendants de l’une des deux populations xériques ne différaient pas de ceux des deux populations de sites humides. Les deux populations avec la plus forte variance génétique additive provenaient de régimes contrastés de précipitation. La différenciation entre populations était faible tant pour chaque trait que pour l’ensemble des traits (Qst = 0.088). Les caractéristiques morphologiques liées à la taille de l’axe principal n’auraient donc que peu signification en termes d’adaptation.• Les résultats suggèrent que le cyprès de Patagonie n’aurait pas développé de pools génétiques adaptés aux optima locaux. Il semble être une espèce phénotypiquement plastique, au moins en ce qui concerne la croissance au stade juvénile.

Seedling response of Nothofagus species to N and P: linking plant architecture to N/P ratio and resorption proficiency

Key messageAs in mature forests, seedlings responded positively to N supply in terms of mass and architecture, especiallyN. obliqua.P became a secondary-limiting nutrient forN. nervosawith increased N addition.AbstractPrevious studies on mature forests of NW Argentinean Patagonia indicated that N is the main growth-limiting nutrient in most dominant tree species, while P limitation is uncommon, despite the soils’ volcanic origin. This pattern was inferred from leaf N/P ratios and resorption proficiencies, but has not been experimentally tested. We conducted a greenhouse trial with seedlings of two deciduous species of high timber quality, Nothofagus nervosa and N. obliqua, and soils characteristic of each species. Seedlings were fertilized with three levels of N (100, 200 and 400xa0mgxa0kg−1 soil) with or without the concurrent application of a single P dose (60xa0mgxa0kg−1 soil) during their second growing season. Response variables were morphological descriptors of shoot and root growth, N and P concentrations in green and senescent leaves and ectomycorrhizal infection. Both species were primarily limited by N: the addition of N resulted in higher shoot and root masses, an increased number of nodes, taller stems and greater basal and root diameters, while no effect of P was found. N/P ratios in green leaves and N and P resorption proficiencies indicate that with increased N availability P can become a secondary-limiting nutrient for N. nervosa. This was accompanied by the maintenance of ectomycorrhizal infection and mass allocation to roots in this species. The steep growth response of N. obliqua to N addition may signal a strong competitive capacity of this species when growing in soils of high N availability.

Differences in phenology and fruit characteristic between invasive and native woody species favor exotic species invasiveness

AbstractnThis study evaluates the idea that differences in reproductive phenology and traits between coexisting exotic and native species may promote exotic invasiveness. Reproductive phenology, proportions of flowers setting unripe fruits and ripe fruits (fruit set), abundance and morphology of fruits, and seed viability were compared between two invasive (Crataegus monogyna and Sorbus aucuparia) and six native woody fleshy-fruited species at three sites in temperate forests of northwestern Patagonia, Argentina. Flowering and the onset of fruit ripening occurred later in the exotic species than in most of the native species. The exotic species differed between them in some aspects of the reproductive process: C. monogyna had a higher fruit set, whereas S. aucuparia produced more flowers which offset its low values of fruit set. In both the exotic species and one simultaneously fruiting native species (Schinus patagonicus), high numbers of ripe fruits with a high proportion of viable seeds remained on the plants at a time when fruits of other native species were either scarce or absent (autumn–winter period). Compared to the fruits of S. patagonicus, those of both the exotic species are larger and fleshier. Therefore, the fruits of both the exotic species offer the dispersers, especially birds which were the most important frugivores in these studied temperate forests, a resource that would not be provided by the native plants. The success of these exotic species in Patagonian forests appears to be attributable in part to differences in their reproductive attributes such as fruit phenology and fruit traits such as size and fleshiness.

Population dynamics of an invasive tree, Sorbusaucuparia, in the understory of a Patagonian forest

Exotic fleshy fruited plants are often dispersed by generalist frugivores into undisturbed or weakly disturbed forests. The establishment and spread of these plants in the understory may pass unnoticed until their abundance and size turns them a nuisance. Sorbus aucuparia is a fleshy fruited tree recently established in temperate forests of northwestern Patagonia. Our aim was to determine the invasion dynamics of S. aucuparia in a Nothofagus pumilio forest. We analyzed age structure, minimum age of reproduction, the time from colonization to effective recruitment (lag time), and demographic parameters to pinpoint critical stages for management. Currently, the population of S. aucuparia is increasing. Large numbers of suppressed, potentially reproductive individuals were found. Lag time was relatively short (25xa0years) in comparison to other invasive woody plants. The minimum reproductive age was 10xa0years, and all reproductive individuals were located in high light conditions. The number of trees at the reproductive stage made the most significant contribution to population growth; a 5xa0% reduction in this number would be enough for the population growth rate to be negatively affected. Thus, the reproductive stage is key to the control of S. aucuparia. Forest disturbance leading to increase light availability may result in higher rates of growth and reproduction among currently suppressed individuals, triggering further expansion events and increasing the number of invasion foci. Management strategies for tree species which present an inconspicuous bank of individuals in the understory, like S. aucuparia, should focus on early detection and eradication of reproductive individuals while avoiding the increase in light availability in the affected environment.

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.

Does water availability regulate biomass partitioning between trunk and branches

The extent to which a vertical trunk is differentiated from its branches is a key trait for the architecture of trees and may affect interspecific relationships. In this study, we analysed the effect of soil water availability on biomass partitioning for Nothofagus pumilio by means of a nursery experiment. Juvenile trees were subject to three irrigation conditions: no irrigation, intermediate irrigation and high irrigation. Irrigation conditions emulated the mean precipitation of the most representative environments inhabited by N. pumilio. Changes in soil water availability modified the biomass partitioning patterns of trees. In comparison to the other two conditions, high irrigation caused: (i) a higher ratio of biomass partitioning to stems than roots; (ii) more trunk growth in relation to its branches; and (iii) more photosynthetic organs relative to the aboveground biomass. Trunk size relative to that of its most recent branches was not increased by water availability. Water availability may play a significant role in the capacity of N. pumilio for space occupation due to the effects on axis differentiation.

Population rules can apply to individual plants and affect their architecture. An evaluation on the cushion plant Mulinum spinosum (Apiaceae)

Growth units of individual plants may be seen as equivalent to individual plants in plant populations. Some of the principles known to rule plant-to-plant interactions in crowded populations may apply to the interactions between growth units in plants.