Javier Grosfeld

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.

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.

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.

Modelo de estados y transiciones de los ñirantales del NO de la Patagonia como herramienta para el uso silvopastoril sustentable

We built a state-and-transition model (S&TM) for the nire forest system under silvopastoral use in northern Patagonia, with the aim to identify management effects on the vegetation. The model can help design practices that maintain the system within desired conditions in the long term. Based on a review of published and unpublished literature, an expert workshop and consultation, and field surveys we proposed alternative states and their response to natural disturbances and current management practices. We defined seven states, 13 degradation and four restoration transitions, and the factors and levels that trigger the transitions (i.e., grazing, firewood extraction, fire and/or dispersal of invasive plants). The best-conserved forest is dominated by nire (Nothofagus antarctica) and cane (Chusquea couleou), while the most degraded state corresponds to sub-shrubby steppes dominated by Acaena splendens (cadillo). The intermediate states are likely to be the most suitable for silvopastoral use (open nire and cane forest, and nire forest with grassland) but are highly unstable. Therefore, with the common current practices, the tree component and cane cover are lost with time. Invasion of exotic species, competition with the herbaceous vegetation, mortality of trees and cane, and soil erosion are the processes that trigger transitions. Most degradation transitions are difficult to revert because they require high-cost practices and/or have a long recovery time. Building the S&TM brought together scattered information about long-term changes in the vegetation. The identification of risk phases enables early warning of degradation.https://doi.org/10.25260/EA.17.27.2.0.240