Effect of Water Deficit Stress on Photosynthetic Characteristics of Jatropha curcas

The need to mitigate climate change cannot be more emphasized, which arises, as a result of increases in CO₂ emissions due to anthropogenic activities. Given the current world energy problems of high fossil fuel consumption which plays a pivotal role in the greenhouse effect, Jatropha curcas biodiesel has been considered a potential alternative source of clean energy (biodiesel is carbon neutral). However, the ability of Jatropha curcas, as a candidate source of alternative of clean energy, to grow in marginal and dry soils, has been poorly elucidated. This study, therefore aimed at investigating whether Jatropha curcas leaves could switch from carrying out C₃ photosynthetic pathway to Crassulacean Acid Metabolism (CAM) as a strategy to improve its water deficit tolerance. Thirty-five-day-old Jatropha curcas accessions, from three different climatic zones of Botswana, viz., Mmadinare (Central zone), Thamaga (Southern zone) and Maun (Northern zone), were subjected to water stress, by with-holding irrigation with half-strength Hoagland culture solution. Net photosynthetic rate, transpiration and stomatal conductance were measured at weekly intervals. The leaf pH was measured to determine whether there was a decrease in pH (leaf acidification) of the leaves during the night, when the plants experienced water deficit stress. All the accessions exhibited marked reduction in all the measured photosynthetic characteristics when experience water deficit stress. However, a measurable CO₂ uptake was carried out by leaves of all the accessions, in the wake of marked decreases in stomatal conductance. There is evidence to suggest that when exposed to water stress J. curcas accessions switch from C₃ mode of photosynthesis to CAM photosynthetic pathway. This is attested to by the slightly low leaf pH at night. Thamaga accession exhibited