Gas exchange efficiency in Cocoa – Spanish elm agroforestry system in the northwest Antioquia, Colombia

Abstract

The cultivation of cocoa (Theobroma cacao L.) under agroforestry systems, generates beneficial environmental conditions for cocoa crop physiology. An experiment was conducted to evaluate the effect of shade trees (Spanish elm trees - Cordia alliodora (Ruiz & Pavon) Oken) planted along with cocoa (clone CCN51) under an agroforestry system on cocoa’s gas exchange parameters regarding the reduction of the light intensity over the cocoa-leaf canopy. The experiment was developed in the Centro de Investigación el Nus - Agrosavia, located in the municipality of San Roque, Antioquia. The experimental design used was a randomized complete block design for the cocoa planting distances from the first row of Spanish elm trees interfacing with the cocoa plantation (4 m, 7 m, 10 m, 13 m). The statistical analysis was performed by estimating the area under the curve (AUC) of each variable, using the trapezoid equation of the statistical environment SAS® 9.4, an analysis of variances was performed to determine if there were statistical differences between treatments, and Tukey’s test at 5% probability was used to estimated statistical differences between means. There were significant differences in the treatments regarding the net photosynthetic rate (A), stomatal conductance (gs), and transpiration rate (E). The highest values of gas exchange parameters were found in the plants located 13 m from elm trees, while the lowest values were presented at 4 m. Plants at 7 m and 10 m always showed intermediate values for all gas exchange parameters. In the same sense, plants at 13 m had a higher radiation use efficiency (RUE) compared to plants at 4 m. The arboreal component modified the environmental conditions on cocoa trees regarding its distribution, generating a differential response to the physiological behavior of cocoa plants.