In most southern provinces of Iran, soil salinity is a growing problem particularly in irrigated agricultural areas and has been found to reduce wheat yields. In order to investigate the effects of various levels of NaCl on some physiological characteristics of two wheat (Triticum aestivum L.) cultivars, an experiment was conducted with four replications in a controlled environment of the greenhouse during 2006 to 2007. Salinity levels were 0, 8 and 12 dS m-1 and wheat cultivars include: Kavir (salt tolerant variety) and Shiraz (salt sensitive variety). The parameters which have been measured include : photosynthetic photon flux density (PPFD) incident on leaf surface, photosynthesis rate (A), sub - stomatal CO2 (Ci), transpiration rate(E) and stomatal conductance of CO2 (gs). These parameters were measured at stem elongation and flowering stages of wheat growth by IRGA. The results showed that PPFD was increased between 8 to 14 O'clock. At both stem elongation and anthesis stages photosynthesis rate, transpiration, stomatal conductance and intercellular CO2 were consistently increased between 8 to 12 O'clock. However, the aforementioned traits were declined from 12 to 14 O'clock due to increasing of leaf temperature. Decrease in photosynthesis in saline conditions was attributed to excess in Na+ and K+ ions. Increasing of these ions in vacuole is leading to an increase in cytoplasm and declining photosynthesis and processes. A substantial reduction in photosynthesis, stomatal conductance and transpiration was detected of exposure to salt stress. In general photosynthesis rate, transpiration, stomatal conductance and Intercellular CO2 of salt tolerant variety (Kavir) was found to be higher than the salt sensitive variety (Shiraz). Thus, it appeared that less adverse effect of salinity on Kavir cultivar may make it more suitable for growth in saline soils found in the investigation.
Key words: Wheat, sodium chloride, photosynthesis, transpiration and stomatal conductance.
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