Alejandro Aparicio

Vegetative propagation of patagonian cypress, a vulnerable species from the subantarctic forest of South America.

Los crecientes riesgos de perdida de recursos geneticos forestales y la necesidad de una produccion sostenible de madera de calidad hacen necesario orientar la investigacion hacia especies arboreas nativas no domesticadas. Para rescatar la diversidad genetica amenazada y como una importante herramienta para el mejoramiento genetico, resulta necesario estudiar la capacidad de las especies para propagarse vegetativamente, asi como desarrollar tecnicas para obtener copias geneticas. El cipres de la cordillera (Austrocedrus chilensis) es una conifera vulnerable del bosque subantartico de Sudamerica, de gran importancia ecologica y potencial economico. Su diversidad genetica se encuentra seriamente amenazada. En este trabajo se examino la capacidad de diferentes genotipos de poblaciones xericas, mesicas y humedas de A. chilensis, para propagarse asexualmente por enraizado de estacas y por injertos. Se analizo ademas la influencia de auxinas exogenas, de la estacion de colecta, del estadio ontogenico de las plantas donantes, de la estacion de injerto y del tipo de pua. La capacidad de enraizado fue muy pobre, tanto para ortets adultos (promedio = 0,27%) como para juveniles (promedio = 2,10%). Solo una progenie juvenil de procedencia xerica mostro resultados remarcables, con 33% de enraizado. Los injertos mostraron buenos resultados a comienzos de primavera usando esquejes vigorosos y semilenosos, con un 80,95% de prendimiento. La compatibilidad entre genotipos de diferentes procedencias usados como pua y portainjertos fue amplia. Estos resultados indican que aunque A. chilensis es una especie de dificil enraizado, su propagacion por injertos es factible utilizando tecnologia de bajo costo.

Heritable variation in the survival of seedlings from Patagonian cypress marginal xeric populations coping with drought and extreme cold

The rear edges of tree species have begun to be perceived as highly valuable for genetic resources conservation and management. In view of expected climatic changes, the responses of trees at their xeric limits may largely be determined by their capacity to cope with augmented environmental variance. We assess the heritability of early survival of Patagonian cypress in two common-garden field tests with contrasting summer water deficits, comprising 140 and 163 open-pollinated families from 10 marginal xeric populations. The first experiment underwent less rigorous conditions than the average mesic, Mediterranean climatic conditions, which were sufficient to reveal additive genetic effects of summer drought on seedling survival. The second trial suffered strong summer water-deficit stress and a winter extreme cold event. In this harsher environment, the heritabilities of survival under summer water-deficit stress were high in all the populations (h2 = 0.84 on average), while the heritabilities of seasonal, extreme cold survival were moderate or even nil (h2 = 0.28 on average). We did not find evidence of genetic differentiation among populations in their capabilities to survive droughts and cold extremes. Our results indicate that even when climatic changes were strong enough to cause the extinction of the most threatened populations, heritable variation for traits underlying drought and cold tolerances may allow the marginal xeric edge of cypress to persist under augmented environmental variance, without losing overall genetic diversity.

Physiological and morphological short-term responses to light and temperature in two Nothofagus species of Patagonia, South America

The study of plant responses to environmental stress factors is essential for management of plant systems and for anticipating their response to climate change. The main goal of this study was to determine morphological and physiological responses of Nothofagus obliqua and N. nervosa seedlings to light and temperature, two of the main stress factors acting in their current natural distribution in NW Patagonia. Responses to light were evaluated analyzing growth and survival, as well as morphological and physiological traits related to them, in seedlings subjected to three contrasting light conditions (full-sun conditions, 50% of sunlight and 20% of sunlight) during one growth season. Temperature photosynthetic responses were evaluated in seedlings subjected to temperature treatments between −5 and 40°C for 2 and 4 h. Growth rate and biomass partition were similar between light treatments in both species. High apical meristem damage and decreased photosynthetic capacity of preformed leaves were observed under full-sun conditions, suggesting that high light levels have a deleterious effect on plant yield. Both species produced neoformed leaves during the growing season with better photosynthetic capacity than preformed leaves under full sun conditions, contributing to plant acclimation. Almost no plasticity was observed in morphological traits in response to shade. Both species differed in optimum temperature for photosynthesis, with a wider temperature range at which high photosynthesis is maintained in N. obliqua. In both species the higher values of net photosynthetic rate were found at higher temperatures than the mean annual temperature of its current natural distribution range. Under no water-stress conditions, future higher temperatures could increase carbon fixation of these species, with a little advantage of N. obliqua if temperature variance is high. Synergy effect of various environmental stress factors, particularly considering cultivation of these species outside their current natural distribution sites require further studies.

Natives helping foreigners?: The effect of inoculation of poplar with patagonian beneficial microorganisms

Inoculation with microorganisms represents an opportunity to enhance tree production, directly affecting plant growth or survival at planting. The aim of the present study was to evaluate the effect of mixed inoculation with native mycorrhizae, two yeasts and one endophytic bacterium, on the growth of two poplar clones commonly used in Patagonia, Argentina. Yeasts and bacteria were selected base on their ability to produce IAA and siderophores, as well as P solubilization in-vitro. A greenhouse trial was performed using hardwood cuttings of Populus nigra ‘Italica’ and Populus trichocarpa ‘SP1456’. Only yeasts modified growth traits, in a host-related response: Tausonia pullulans reduced the root/shoot ratio in P. nigra, and Candida saitoana and increased shoot dry biomass in P. trichocarpa. All plants presented arbuscular mycorrhizal colonization but ectomycorrhizae were absent. Two types of arbuscular mycorrhizal colonization were observed, one of them similar to Glomus tenue. We found a tendency for a higher percentage of arbuscular mycorrhizal colonization when plants were inoculated with T. pullulans. The used of native yeast along with mycorrhizal inocula appears to be a promising tool to improve poplar forestry.