Combined Effects of Salinity and Iron Availability on Growth, Gas Exchange, and Antioxidant Status of Foeniculum vulgare

The combined effect of NaCl salinity and iron deficiency on biomass production, iron homeostasis, photosynthetic activity and antioxidant status were studied in Foeniculum vulgare: a biannual Apiaceae with pastoral potential. Plants were grown in hydroponic conditions for 21 days under two concentration of iron: 1 (low) or 40 µM Fe³⁺-EDTA (sufficient), in the absence or presence of 75 mM NaCl. When individually applied, both Fe deficiency and salinity notably restricted shoot and whole dry weight (DW) with a more marked effect under combined stresses. This may linked to a significant decrease in stomatal conductance, CO₂ assimilation rate (84%) and transpiration rate (66%). Although, the relatively better tolerance to Fe deficiency combined with salinity could be explained by the capacity of this species to maintain higher root system and root/shoot DW ratio. Salinity has a negative impact on Fe-use efficiency (24%) when combined with a low Fe supply that means that iron is primarly used in shoot sodium (Na⁺) excretion. Phenolic analysis showed the relevance of caffeic and cinnamic acid derivatives in leaves and roots proving their modulation under D and (D + S) treatments. Antioxidant activities as well as inhibitory capacity towards LOX enzyme were ound to be altered under D and (D + S) conditions as rescued by the lowest IC50 and EC50 values. Overall, F. vulgare constitues a promising model to ameliorate the tolerance of the cultivated fennel species under low Fe soils and/or saline regions.