SUMMARYThis study deals with the ecophysiological response of Criollo cacao cultivars to water deficit during initial establishment phase in an agroforestry system under shade of four timber species using a randomised block design. CO2 assimilation rate (A), transpiration (E) and stomatal conductance (gs), water potentials, pressure–volume curves and fluorescence measurements were studied during two dry and wet seasons. Survival rates, basal diameter and leaf concentrations of K, P and N were also determined. All cultivars exhibited 60% reduction in gs with drought, resulting in 73% decrease in A and E. Despite lower A, electron-transport rates were not significantly affected, suggesting the existence of electron sinks. Photochemical quenching is negatively affected by drought in some cultivars, whereas relative quantum yield of photosystem II and non-photochemical quenching remained the same during both the periods. Cultivars with the highest osmotic adjustment coincided with the highest survival rates, whereas growth and leaf nutrient concentrations were similar in all cultivars.

We studied physiological traits of 12 Criollo cocoa cultivars growing in a germplasm bank in the southern region of Maracaibo Lake Basin, during the rainy (RS) and dry seasons (DS) of 2007. A further evaluation of photosynthetic responses to changes in environmental parameters was done on three cultivars: Los Caños 001 (LCA001), Sur Porcelana 010 (SP010) and Escalante 001 (ESC001) in 2009 and 2010. Leaf water potential ( L ) of most cultivars decreased during the DS of 2007, with the exception of ESC001. Maximum photosynthetic rate (A max ), stomatal conductance and water use efficiency varied among cultivars and seasons. The CO 2 -saturated photosynthetic rate (A CO2sat ) was higher in LCA001 and ESC001 than in SP010, with no differences in carboxylation efficiency. Light curve responses of the three cultivars were similar. In all cultivars, no evidence of chronic photoinhibition was observed, since maximum quantum yield of photosystem II was high (0.77-0.81). We conclude that ESC001 has the best physiological performance ( L remained unchanged, highest A max , A CO2sat and photochemical activity), and it seems to be a promising cultivar for cocoa agroforestry systems in the southern region of Maracaibo.

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. , 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. Key words: A/C curves, fluorescence, photosynthetic activity, Theobroma cacao, water potential. ¿Tiene el cacao Criollo las mismas características ecofisiológicas que el Forastero? ResumenAntecedentes: 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 CO 2 (C i ) y a la densidad de flujo de fotones (PFD), la relación de isótopos de carbono (δ 13 C), la proporción de isótopos de nitrógeno (δ 15 N), 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 árbo-les de cacao Forastero, por lo tanto ambos podrían ser recomendados como materiales adecuados para el cultivo en ambientes similares al lugar de estudio, aumentando así el cultivo de cacao de alta calidad.

The photosynthetic capacity of C. procera was higher than that of C. gigantea. During the DS, A was regulated by stomatal and non-stomatal factors in a coordinated manner and drought did not cause chronic photoinhibition. A higher density of trichomes and leaf angle in C. gigantea may contribute to the maintenance of A and confer more efficient protection of photochemical activity in the DS. Ecophysiological traits such as high photosynthetic rate throughout the year even during the DS, and high WUE, highly pubescent leaves and low SLA observed in both species contribute to the establishment and growth of Calotropis in dry conditions.

Evidence for the operation of CAM in the deciduous climber, Cissus trifoliata L., was obtained in field and laboratory studies. Under natural conditions, diurnal oscillations of titratable acidity and colorimetric measurements of night CO fixation, determined for a period of two and a half years, suggested that acid accumulation was related to plant water status, assessed through the daily courses of stomatal resistance and xylem water potential during dry and rainy seasons. These findings were confirmed by gas exchange studies under controlled conditions which showed that the plant fixed all its CO during the day when it was well irrigated; as water stress increased, dark CO uptake gradually replaced fixation during the day until the plant only performed dark fixation. In severe water stress, even the rate of the latter process decreased until leaves fell.