Leaf morphophysiological changes induced by long-term drought in Jatropha curcas plants explain the resilience to extreme drought

Jatropha curcas plants were cultivated during 4 months in pots containing soil at 90% of field capacity (FC), in permanent drought at 30% of FC and in extreme drought without any irrigation. The permanent drought clearly resulted in significant reductions of 43% on spongy parenchyma thickness and increase of 170% on stomatal index and 80% in photosynthetic pigments content. The measurements of leaf gas showed that growing in permanent drought condition resulted in decreases of 38% on net CO2 assimilation rate, 81% on stomatal conductance, 69% on transpiration, 30% on intercellular carbon concentration (Ci) and reductions on the capacity to refresh leaves. The plants subjected to extreme drought took a period of 12 days of re-irrigation to recover values of CO2 assimilation and stomatal conductance similar to well-irrigated plants. Some of these morphophysiological changes look as though not to directly result from drought, but from secondary variations unleashed by stomatal closure and intensified by long duration of stressful conditions. This seems to result in plants photosynthetically more efficient with competitive advantage in arid situations. Besides these variations, it was possible to show and evaluate the resilience and extreme tolerance of these plants to survive in harsh environment.