Efecto del manejo silvopastoril sobre la estructura demográfica del dosel y la composición del sotobosque en bosques mixtos de ciprés de la cordillera (<i>Austrocedus chilensis</i>) y coihue (<i>Nothofagus dombeyi</i>)

Los bosques mixtos de ciprés de la cordillera y coihue del noroeste de la Patagonia se encuentran influenciados por fuertes presiones antrópicas como el uso silvopastoril sin un manejo sustentable. Los efectos de esta actividad tienen la capacidad de generar fuertes y diversos impactos negativos. En tres establecimientos productivos se estudiaron los cambios demográficos de la comunidad de dosel y la estructura de la vegetación del sotobosque en bosques bajo diferentes intensidades de uso silvopastoril. La intensidad de uso no tuvo un efecto significativo sobre la estructura demográfica de la población. Sin embargo, la complejidad y la heterogeneidad del sotobosque fueron mayores en los sitios con alta intensidad de uso. Si bien al momento incrementos en la intensidad de uso no estaría comprometiendo la perpetuidad del recurso forestal, los cambios documentados en el sotobosque indican posibles cambios en los patrones de desarrollo de los mismos.The mixed forests of cypress and coihue of northwestern Patagonia are influenced by strong human pressures, such as silvopastoral use without sustainable management. The effects of this activity have the ability to generate strong and diverse negative impacts. In three production facilities we studied changes in demography of the community canopy and in the structure of understory vegetation in forests under two silvopastoral use intensities. The intensity of use had no significant effect on the demographic structure of the population. However, the complexity and heterogeneity of understory were higher at sites with high intensity of use. Although when increases in the intensity of use would not compromise the permanence of forest resources, changes documented in the understory indicate possible changes in the patterns of their development.Eje: A1: Sistemas de producción de base agroecológicaFacultad de Ciencias Agrarias y Forestale

Efecto del manejo silvopastoril sobre la estructura demográfica del dosel y la composición del sotobosque en bosques mixtos de ciprés de la cordillera (<i>Austrocedus chilensis</i>) y coihue (<i>Nothofagus dombeyi</i>)

Los bosques mixtos de ciprés de la cordillera y coihue del noroeste de la Patagonia se encuentran influenciados por fuertes presiones antrópicas como el uso silvopastoril sin un manejo sustentable. Los efectos de esta actividad tienen la capacidad de generar fuertes y diversos impactos negativos. En tres establecimientos productivos se estudiaron los cambios demográficos de la comunidad de dosel y la estructura de la vegetación del sotobosque en bosques bajo diferentes intensidades de uso silvopastoril. La intensidad de uso no tuvo un efecto significativo sobre la estructura demográfica de la población. Sin embargo, la complejidad y la heterogeneidad del sotobosque fueron mayores en los sitios con alta intensidad de uso. Si bien al momento incrementos en la intensidad de uso no estaría comprometiendo la perpetuidad del recurso forestal, los cambios documentados en el sotobosque indican posibles cambios en los patrones de desarrollo de los mismos.The mixed forests of cypress and coihue of northwestern Patagonia are influenced by strong human pressures, such as silvopastoral use without sustainable management. The effects of this activity have the ability to generate strong and diverse negative impacts. In three production facilities we studied changes in demography of the community canopy and in the structure of understory vegetation in forests under two silvopastoral use intensities. The intensity of use had no significant effect on the demographic structure of the population. However, the complexity and heterogeneity of understory were higher at sites with high intensity of use. Although when increases in the intensity of use would not compromise the permanence of forest resources, changes documented in the understory indicate possible changes in the patterns of their development.Eje: A1: Sistemas de producción de base agroecológicaFacultad de Ciencias Agrarias y Forestale

The magnesium-protoporphyrin IX (oxidative) cyclase system. Studies on the mechanism and specificity of the reaction sequence.

Mg-protoporphyrin IX monomethyl ester cyclase activity was assayed in isolated developing cucumber (Cucumis sativus L. var. Beit Alpha) chloroplasts [Chereskin, Wong & Castelfranco (1982) Plant Physiol. 70, 987-993]. The presence of both 6- and 7-methyl esterase activities was detected, which permitted the use of diester porphyrins in a substrate-specificity study. It was found that: (1) the 6-methyl acrylate derivative of Mg-protoporphyrin monomethyl ester was inactive as a substrate for cyclization; (2) only one of the two enantiomers of 6-beta-hydroxy-Mg-protoporphyrin dimethyl ester had detectable activity as a substrate for the cyclase; (3) the 2-vinyl-4-ethyl-6-beta-oxopropionate derivatives of Mg-protoporphyrin mono- or di-methyl ester were approx. 4 times more active as substrates for cyclization than the corresponding divinyl forms; (4) at the level of Mg-protoporphyrin there was no difference in cyclase activity between the 4-vinyl and 4-ethyl substrates; (5) reduction of the side chain of Mg-protoporphyrin in the 2-position from a vinyl to an ethyl resulted in a partial loss of cyclase activity. This work suggests that the original scheme for cyclization proposed by Granick [(1950) Harvey Lect. 44, 220-245] should now be modified by the omission of the 6-methyl acrylate derivative of Mg-protoporphyrin monomethyl ester and the introduction of stereo-specificity at the level of the hydroxylated intermediate

Porphyrin thin films coated quartz crystal microbalances prepared by electropolymerization technique

Quartz crystal microbalances (QMB) have been coated by thin films of different metal complexes of protoporphyrin IX dimethyl ester (M-PPIX), deposited by electropolymerization technique. The structure of these films has been characterized by scanning tunnelling microscopy (STM). The sensory behaviour of the obtained QMB have been studied in the presence of four volatile organic compounds (VOC)