Physiological Responses to Drought Stress in Jatropha curcas Seedlings

Aims: The aim of the study was to investigate the physiological mechanisms of Jatropha curcas seedlings exposed to drought and the possible influence of seedling age. Study Design: A pot experiment was carried out using a completely randomized design with two seedling ages (2- and 3-month-old seedlings), two treatments per age (Watered: fully irrigated, and Unwatered: Not irrigated), six replicates (24 pots). Place and Duration of Study: The experiment was performed in a greenhouse facility located at the Experimental Station “Mauro Deidda” (Department of Agriculture of University of Sassari) at Ottava (Sassari, Italy) between June and September 2011. Methodology: To investigate the responses of 2- and 3-month-old J. curcas seedlings exposed to drought stress on 4th, 8th, 12th, 19th, and 26th day from treatment’s beginning, leaf and soil water content, biometric, gas exchange, and chlorophyll a fluorescence measurements were performed; on 26th day from treatment’s beginning, biometric destructive measurements were carried out. Results: Results support the hypothesis that J. curcas is appropriate to be cultivated in areas with limited water availability or prolonged periods of drought and highlight that mechanisms of drought response are highly influenced by seedling age. J. curcas seedlings maintained a good leaf water status by means of an effective stomatal closure, associated with a reduced aboveground growth and an increased root:shoot ratio. Under drought stress, 2-month seedlings showed a higher allocation of resources to roots compared to 3-month seedlings. Drought resulted in more detrimental effects on the photosynthetic response of 3-month seedlings, inducing the reduction of stomata conductance and the loss of photosystem II integrity. 2-month seedlings were instead able to activate mechanisms of drought tolerance through the activation of excess energy dissipation mechanisms. Conclusion: In the early stage of crop establishment, the transplanting of J. curcas 2-month seedlings proved to be more effective in order to avoid water stress related consequences