ABSTRACT
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 an earlier stomatal closure than the other two accessions. This
resulted in Thamaga accession displaying a slightly lower dry weight than both
Mmadinare and Maun accessions. It could be concluded
that Jatropha curcas appeared to tolerate water deficit stress due to
its ability of switching
from C3 photosynthetic pathway to the CAM photosynthetic pathway, but with a cost to biomass accumulation, as
demonstrated by slightly more reduced CO2 assimilation by Thamaga
accession, than the other two accessions.