Abstract:In a global context in which obtaining new energy sources is of paramount importance, the production of biodiesel from plant crops is a potentially viable alternative to the use of fossil fuels. Among the species used to produce the raw material for biodiesel, Jatropha curcas L. (JCL) has enjoyed increased popularity in recent years, due partly to its ability to grow in degraded zones and under arid and semi-arid conditions. The present study evaluates the potential for JCL production under irrigation with non-conventional water resources in abandoned agricultural soils of the island of Fuerteventura (Canary Islands, Spain), which is one of the most arid parts of the European Union. JCL growth and productivity are compared during the first 39 months of cultivation in two soil types (clay-loam and sandy-loam) and with two irrigation water qualities: recycled urban wastewater (RWW) and desalinated brackish water (DBW). The results indicate that JCL growth (in terms of plant height and stem diameter) was significantly influenced both by soil type and water quality, with better development observed in the sandy-loam soil under RWW irrigation. Productivity, measured as cumulative seed production, was not affected by soil type but was affected by water quality. Production under RWW irrigation was approximately seven times greater than with DBW (mean ~2142 vs. 322 kg·ha 6903 were found to be key factors in the greater productivity observed under irrigation with this type of water.

Salinity is often a great limitation in marginal environments with potential for developing alternative non‐edible crops for biodiesel, and the physiological responses involved in the recovery of plants subjected to high salinity are poorly studied. The aim of this study on Jatropha curcas is to identify salinity tolerance responses of net photosynthesis rate under saturating irradiances (Amax), its recovery capacity and the role of mesophyll conductance (gm) over Amax. Two experiments were performed with seedlings in pots under outdoor conditions and hydroponic conditions, respectively, with salinity intensities ranging from 3 to 12 dS/m, their isosmotic treatments with polyethylene glycol (PEG) and controls without abiotic stress. Amax and growth rate were mainly affected by salinity effects in all the ranges, with a drastic 60% drop in dry biomass under 6 dS/m, revealing a significant sensitivity of this species. However, a surprising increase in Amax was promoted by the presence of NaCl, with respect to their respective isosmotic treatments with PEG, although it was still lower than the unstressed plants. This advantage disappeared from 9 dS/m, but negative effects of NaCl toxicities were never detected. The photochemical apparatus resulted extremely resistant in this species, since Fv/Fm and leaf greenness were affected only at 12 dS/m. So, gm was strongly and linearly associated with Amax. This association derives from the overall range of stress intensities tested, thus appearing as the main useful trait for enhancing photosynthesis depletion under salinity stress, without losses of the water use efficiency. A drastic 75% drop was also detected in the electron use for photosynthesis, revealing that Amax would also be modulated by metabolic impairments under salinity. Moreover, full recovery after only 8 days was observed, confirming the high resistance of the species to NaCl stress even under very high salinities. This study contributes to a better understanding of the physiological processes involved in the response of J. curcas to salinity during early vegetative stage, generating possibilities for improving tolerance of this species under environments exposed to salinity.

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