Effects of Shading on the Frost Damage and Photosynthesis of Jatropha curcas L. in Gaborone, Botswana

Abstract

Jatropha (Jatropha curcas L.) is well-adapted to arid areas and thus has been recognized as a new energy crop for bio-diesel production in Africa. Low temperatures due to radiative cooling effects are known to cause frost damage to jatropha and this is an important limiting factor of its cultivation in Gaborone, Botswana. To mitigate heat loss at night and rapid increments of light intensity and air temperature after dawn, shading screens were applied to field-grown jatropha. Then, the protection effects and the photosynthesis after being damaged by frost were examined. Cold waves severely damaged branches and leaves of jatropha trees; however, this damage was greatly alleviated by the shading treatments. Without shading, nearly half of the branches showed blackened apexes and most of the leaves had fallen off, while only a few branches were damaged and a number of leaves were maintained in the shading plots. The number of inflorescences was also higher in these plots though it was investigated earlier than the flowering period, therefore further observation is surely necessary. Photosynthesis measurements suggested that shading significantly reduced CO₂ assimilation and transpiration rates of jatropha leaves due to the limited sunlight, yet the shaded leaves properly functioned in response to changing light intensity. From these results, it was concluded that shading was an effective technique to protect jatropha branches and leaves from frost damage, which may have further improved inflorescence formation as well. Shading screens need to be removed after winter to increase light availability and enhance photosynthetic ability.