IRRIGATION WATER SALINITY LIMITS FABA BEAN (VICIA FABA L.) PHOTOSYNTHESIS

Determination of plant salt stress responses is essential for stabilization of crop productivity under saline conditions. It is known that high soil salinity may adversely affect photosynthesis, which is a prerequisite for biomass production. For this reason, there is a considerable interest in measuring the photosynthetic rate of horticultural crops under saline conditions. A greenhouse pot experiment was set up to study the effects of saline irrigation water on faba bean (Vicia faba L.) photosynthetic rate and chlorophyll content index. Faba bean seedlings were transplanted into pots and treated with saline irrigation water. NaCI salinity was applied in a nutrient solution as follows: NaCl₀ — control (basic nutrient solution without added NaCI), NaCl₅₀ (control + 50 mM NaCl) and NaCl₁₀₀ (control + 100 mM NaCI). Five weeks after salinity treatment started faba bean leaf intercellular CO₂ concentration (Ci), stomata! conductance (g_s), transpiration rate (E), photosynthetic rate (A) and chlorophyll content index (CCI) were measured. Stomatal conductance, transpiration rate and photosynthetic rate of faba bean plants irrigated with saline water significantly decreased (P<0.01) in regard to control plants,  but without significant difference amongst treatments.  Intercellular CO₂ concentration was not significantly affected by application of saline irrigation water. Salinity treatments significantly altered (P=0.01) chlorophyll content index, although the influence was not linear to the salinity treatments. Raised soil salinity imposed water limitation for faba bean plants, which was suggested by lower stomatal conductance. Plant adaptive responses to salt stress include retention of water by stomatal closure, decreasing both transpiration and photosynthetic rate. Therefore application of saline irrigation water results in decreased rate of transpiration and limits faba bean photosynthesis as well.