Ludmila La Manna

Hydraulic differences along the water transport system of South American Nothofagus species: do leaves protect the stem functionality?

Hydraulic traits were studied for six Nothofagus species from South America (Argentina and Chile), and for three of these species two populations were studied. The main goal was to determine if properties of the water conductive pathway in stems and leaves are functionally coordinated and to assess if leaves are more vulnerable to cavitation than stems, consistent with the theory of hydraulic segmentation along the vascular system of trees in ecosystems subject to seasonal drought. Vulnerability to cavitation, hydraulic conductivity of stems and leaves, leaf water potential, wood density and leaf water relations were examined. Large variations in vulnerability to cavitation of stems and leaves were observed across populations and species, but leaves were consistently more vulnerable than stems. Water potential at 50% loss of maximum hydraulic efficiency (P(50)) ranged from -0.94 to -2.44 MPa in leaves and from -2.6 to -5.3 MPa in stems across species and populations. Populations in the driest sites had sapwood and leaves more vulnerable to cavitation than those grown in the wettest sites. Stronger diurnal down-regulation in leaf hydraulic conductance compared with stem hydraulic conductivity apparently has the function to slow down potential water loss in stems and protect stem hydraulics from cavitation. Species-specific differences in wood density and leaf hydraulic conductance (K(Leaf)) were observed. Both traits were functionally related: species with higher wood density had lower K(Leaf). Other stem and leaf hydraulic traits were functionally coordinated, resulting in Nothofagus species with an efficient delivery of water to the leaves. The integrity of the more expensive woody portion of the water transport pathway can thus be maintained at the expense of the replaceable portion (leaves) of the stem-leaf continuum under prolonged drought. Compensatory adjustments between hydraulic traits may help to decrease the rate of embolism formation in the trees more vulnerable to cavitation.

Caracterización de los suelos bajo bosque de Austrocedrus chilensis a través de un gradiente climático y topográfico en Chubut, Argentina

Los bosques de Austrocedrus chilensis (Cipres de la cordillera) se desarrollan en la region andino-patagonica, abarcando en Argentina un area de alta heterogeneidad ambiental. En este trabajo se caracterizaron los suelos donde se desarrollan bosques de A. chilensis, a traves de un gradiente topografico y de precipitacion en la provincia de Chubut. Se seleccionaron 8 sitios de muestreo correspondientes a bosques puros y compactos de A. chilensis, abarcando un rango latitudinal aproximado desde 42°0 hasta 43°14 L.S. En cada sitio de muestreo se caracterizaron las propiedades morfologicas, fisicas y quimicas del suelo. Los bosques de A. chilensis se desarrollaron sobre suelos de diferentes materiales parentales: depositos glacifluviales, aluviales, andesita, ceniza y pumita. Los suelos volcanicos presentaron discontinuidades litologicas, ya sea glacifluvial o material rocoso. En general, los suelos presentaron horizontes superficiales oscuros, ricos en materia organica (8,5 a 14,6%), con bajas densidades aparentes (0,57 a 0,97 g/cm³), y pH en agua neutro o ligeramente acido todo a lo largo del perfil. Sin embargo, los diferentes materiales parentales determinaron grandes variaciones en textura (arcillosa a arenosa), contenido de fragmentos gruesos (0 a 50%), profundidad de suelo (35 a 140 cm), grado de alofanizacion (nulo a alto), contenido de humedad equivalente, etc. Los resultados evidenciaron la capacidad de A. chilensis para desarrollarse en suelos muy disimiles, desde suelos someros, arcillosos y con caracteristicas verticas, hasta suelos volcanicos profundos.

Características estructurales de los bosques de Austrocedrus chilensis afectados por "mal del ciprés" en Patagonia, Argentina

Resumen es: La distribucion de los bosques de Austrocedrus chilensis incluye un area de alta variabilidad climatica, topografica y edafica. Estos bosques sufren un p...

Spatial and temporal patterns at small scale in Austrocedrus chilensis diseased forests and their effect on disease progression

Austrocedrus chilensis is an endemic conifer of Patagonia that suffers a widespread mortality whose causes are a topic of discussion. Since Phytophthora austrocedrae is the most probable cause, we proposed that the spatial and temporal patterns of disease at small scale should reflect pathogen behavior. We aimed at characterizing the spatial and temporal patterns of diseased trees in different soil types and the effect of microsite variability on diseased trees spatial pattern. The spatial pattern of disease was influenced by soil type and tree density. In clay soils with low disease incidence (ca. 25%), the spatial pattern was random and not influenced by abiotic microsite conditions. When disease incidence increased (ca. 70%), concurring with denser plots, the spatial pattern was clustered, as a result of an infection process, and it was independent of microsite variability. In soils with better drainage conditions, that is, alluvial soils with volcanic ash input and coarse textured volcanic soils, the disease was clustered and associated with flat microtopographies. The progression of the disease at small scale was influenced by soil, precipitation and tree density. The spatial and temporal patterns of disease progression were associated with a contagion process and with environmental variables that affect drainage, coinciding with Phytophthora biology and requirements. Our results concur in pointing at Phytophthora as the cause of A. chilensis disease in the study area. Management practices should be urgently applied in order to minimize the spread of the inoculum.

Applying cost-distance analysis for forest disease risk mapping: Phytophthora austrocedrae as an example

AbstractCost-distance model analyzes the relative difficulty in reaching each spot of the landscape for the object or species under study. It calculates the effective distance, which is the Euclidian distance modified by the friction to movement through different landscape elements. This work deals with the application of cost-distance analysis in forest pathology, considering Austrocedrus chilensis root rot caused by Phytophthora austrocedrae as an example. In this case, cost-distance analysis was used to determine the relative difficulty for the pathogen to reach healthy forest patches from the patches that are presently diseased. Friction values were assigned on the basis of abiotic conditions, biological characteristics of the pathogen and host presence. Since cattle may be a vehicle for Phytophthora dispersion, three hypothetical situations of ranching were considered. Cost-distance application resulted useful to define minimum risk areas for conservation purposes. In the study case, minimum risk area strongly varied in response to cattle presence. This study provided valuable information for A. chilensis disease management and showed one of the broad applications of cost-distance analysis in forestry.

Distribución y caracterización del daño ocasionado por Pissodes castaneus en plantaciones de Pinus spp. de la región Andino Patagónica Argentina

El primer registro de Pissodes castaneus (Col.: Curculionidae) en la region Andino Patagonica fue realizado en 2005 en la provincia de Neuquen. Este insecto ataca coniferas del genero Pinus, generalmente debilitadas por factores bioticos o abioticos. En algunas plantaciones constituye el unico problema sanitario, sin embargo, se desconoce su area de distribucion y los niveles de dano en la region. Los objetivos del trabajo fueron: 1) determinar la distribucion actual de la especie en la region Andino Patagonica, 2) tipificar y cuantificar el dano ocasionado por Pissodes castaneus en plantaciones de la provincia de Chubut, y 3) evaluar la asociacion entre intensidad de ataque y caracteristicas silvicolas y ambientales de las plantaciones en la provincia de Chubut. La especie fue registrada en las provincias de Neuquen, Rio Negro y Chubut, siendo proporcionalmente mayor el numero de plantaciones infestadas en las dos ultimas. Los porcentajes de infestacion variaron entre 1,4 y 45,7 %. Pinus contorta var. murrayana resulto mas afectado y, en orden de importancia, le siguieron Pinus radiata y Pinus ponderosa. La mayor mortalidad se registro en Pinus contorta var. murrayana. En plantaciones jovenes de Pinus ponderosa fue registrado como el unico agente de dano, ocasionando la muerte por anillamiento. El grado de infestacion estuvo positivamente asociado con la presencia de residuos forestales y con el ataque de Sirex noctilio. Las caracteristicas del ataque observado en la region, sumadas a la distribucion que ha alcanzado la especie, exigen que Pissodes castaneus sea considerado en la definicion de pautas de manejo.