Abstract: Background: The Palma Real Mountain of Venezuela has Criollo and Forastero cocoa trees of over 50 years old. These individuals are considered ancestral representatives of high quality cocoa that have survived for many years in this location without any agronomic management. Question: This study shows some physiological traits of these old trees, in order to determine whether differences exist in photosynthetic capacity and some biochemical parameters between the two types of cocoa growing under natural conditions. Studied species: Theobroma cacao L. Study site and years of study: was done in the mountain Palma Real in the Island of Margarita, Edo. Nueva Esparta, in January 2008 and November 2009. Methods: The individuals present in the area were initially characterized as Criollo or Forastero and gas exchange, chlorophyll fluorescence and the response of the photosynthetic rate (A) to intercellular CO2 concentration (Ci) and photosynthetic photon flux density (PFD), carbon isotope ratio (δ13C), nitrogen isotope ratio (δ15N), leaf N and chlorophyll content were evaluated. Results: The results showed that the gas exchange characteristics of Criollo cocoa differ slightly from those of Forastero. However, similar PFD saturation (~400 μmol m-2 s-1) with values of A at saturating light approaching 4 μmol m-2 s-1, carboxylation efficiency (CE) and photochemical activity, indicated a comparable photosynthetic capacity in both cocoa types. Conclusions: There are apparently no physiological disadvantages in Criollo compared with Forastero trees and therefore both could be recommended as suitable materials for cultivation in similar environments, thereby expanding cultivation of high quality cocoa.
Resumen: Antecedentes: La Montaña Palma Real en Venezuela tiene árboles de cacao Criollo y Forastero de más de 50 años de edad. Estos individuos se consideran representantes ancestrales de cacao de alta calidad que han sobrevivido durante muchos años en este lugar sin ningún tipo de manejo agronómico. Pregunta: Este estudio muestra algunas características fisiológicos de estos árboles, con el fin de determinar si existen diferencias en la capacidad fotosintética y algunos parámetros bioquímicos entre los dos tipos de cacao que crecen en condiciones naturales. Especie estudiada: Theobroma cacao L. Sitio de estudio y años del estudio: se hizo en la montaña Palma Real en la Isla de Margarita, Estado Nueva Esparta, en enero de 2008 y noviembre de 2009. Métodos: Los individuos presentes en la zona, inicialmente se caracterizaron como cacao Criollo o Forastero; se evaluó el intercambio gaseoso, la fluorescencia de la clorofila, la respuesta de la tasa fotosintética (A) a la concentración intercelular de CO2 (Ci) y a la densidad de flujo de fotones (PFD), la relación de isótopos de carbono (δ13C), la proporción de isótopos de nitrógeno (δ15N), y el contenido de clorofila y N foliar. Resultados: Los resultados mostraron que las características de intercambio de gases de cacao Criollo difieren levemente de los de cacao Forastero. Sin embargo, la PFD de saturación fue similar (~ 400 μmol m-2 s-1) con valores de A a luz saturante cerca de 4 μmol m-2 s-1, la eficiencia de carboxilación (CE) y la actividad fotoquímica, indicaron una capacidad fotosintética comparable en ambos tipos de cacao. Conclusiones: Aparentemente no hay desventajas fisiológicas en el cacao Criollo en comparación con los árboles de cacao Forasteropor lo tanto ambos podrían ser recomendados como materiales adecuados para el cultivo en ambientes similares al lugar de estudioaumentando así el cultivo de cacao de alta calidad
Nicotiana glauca, a shrub native to southern South America, is widely distributed in the Americas, from Patagonia to the USA, from zero up to 3,700 m; it rapidly invades disturbed environments. In Venezuela, it has been reported from zero up to 2,000 m growing in contrasting conditions of relative humidity, temperature, rainfall, and salinity. In order to gain insight into the extent and mode of resistance to drought and salinity in N. glauca, we studied the effect of these factors on water relations and photosynthesis under both natural and greenhouse conditions. In the field, water potential, photosynthetic rate (A) and stomatal conductance (gs), but not relative water content (RWC) decreased because of drought. Manual removal of epicuticular wax increased excess energy dissipation through non-photochemical quenching without altering the capacity of photochemical quenching. In the greenhouse, water deficit as well as salinity resulted in osmotic adjustment; at the end of the experiment, turgor potential and RWC under water deficit were similar to control and higher under salinity. Water deficit and salinity caused marked decreases in A and gs. There were very few or no changes with natural drought, salinity or experimental water deficit in potential quantum efficiency of PSII, which could be explained partly by an increased non-photochemical quenching. We conclude that the partial tolerance to drought and salinity in plants of N. glauca resides in their ability to achieve water conservation through stomatal closure and osmotic adjustment, reduce absorption of excess radiation through the presence of leaf wax and dissipate it through increased non-photochemical quenching. All these characteristics confer plants of N. glauca advantages to invade disturbed areas, subject to salinity and/or seasonal drought under high irradiance.
Vegetative as well as reproductive phenology of tropical trees frequently occur synchronously at the end of the dry season. It has been repeatedly observed on two individuals of the tropical species Ficus obtusifolia growing in Caracas that they lose their entire foliage in a period of 48 h during the dry season and renew it within the next 72 h. In order to gain knowledge on the mechanisms that govern leaf exchange in F. obtusifolia, we followed in these two individuals the seasonal changes in leaf and fruit phenology, water relations and environmental variables, and in another 25, phenology only. Although foliar exchange was always observed before the rainy season, it also occurred near the end of the rainy season. An increase in leaf turgor potential of mature leaves and a low sap flow velocity coincided with leaf fall. Foliar exchange in all 27 individuals, growing in locations with different elevation and, possibly, access to underground water, was bi-modal and occurred in a period of approximately one month around both equinoxes. The presence of fruits was also bi-modal, occurring after leaf renewal. The sequence of phenological events repeated itself in all the individuals studied, although with inter-annual and individual variations in date of foliar exchange. Leaf fall was independent of leaf water status and significantly correlated with, in decreasing order, day length, minimum air temperature, rainfall, maximum air temperature and total radiation. We conclude that in F. obtusifolia high nocturnal temperature, increasing daytime temperature and radiation, and low cloud cover apparently drove foliar exchange. Day length showed a strong correlation with leaf renewal possibly to due to the significant relationships between day length and environmental variables. Direct effects of day length alone were not evidenced, as foliar exchange took place during a long time-span around the equinoxes.