The tolerance of Jatropha curcas seedlings to NaCl: an ecophysiological analysis

Abstract

Jatropha curcas L. is a biodiesel crop that is resistant to drought stress. However, the salt tolerance of this plant has not yet been studied. To address this question, J. curcas seedlings were grown in a fertilised substrate to evaluate the effects of salinity stress on growth, leaf water relation and organic solutes, leaf and root mineral concentrations, chlorophyll fluorescence parameters, and carbohydrate concentration. The experiment consisted of six treatments with different concentrations of NaCl in the irrigation water: 0 (control), 30, 60, 90, 120 and 150 mM. The total biomass exhibited a salt-induced decrease in the 60 mM or higher NaCl concentrations. The Cl(r) concentration was higher than the Na(+) concentration in all of the plant tissues. The water potential and relative water content of the leaves were not affected by any of the salt treatments. However, salinity induced a decline in the leaf K(+) concentration, together with a significant enhancement in the leaf P, S, Fe, Zn, Mn and Cu levels. The net assimilation of CO₂ also decreased with the salt treatment, due in part to non-stomatal limitation from the increase in C(a)/C(i) and a decrease in the maximum quantum efficiency (F(v)/F(m)) of photosystem II and soil plant analysis development (SPAD) units. This work suggests that J. curcas seedlings exhibit a moderate tolerance to salinity, as the plants were able to tolerate up to 4 dS m(-1) (EC water irrigation; 30 mM NaCl). The negative influences of salinity in this crop are mainly due to Cl(r) and/or Na(+) toxicity and to a nutritional imbalance caused by an increase in the Na(+)/K(+) ratio. The osmotic effect of salinity in this species is negligible, perhaps due to its strong control of leaf transpiration, which reduces water loss.