Physiological Responses of Iranian Alfalfa (Medicago sativa) Ecotypes to Salt Stress as One of Deleterious Impacts of Climate Change
ABSTRACT Definitely the physiological processes of plants are related to the deleterious influences of climate change impacts on plants. To identify some salt tolerant ecotypes from its centre of origin in Iran, a study was conducted on the physiological responses of genotypes of alfalfa to salt stress at mature plant. Five Iranian alfalfa ecotypes that they were representative of 3 climates zone were evaluated to salt stress in a split plot trial with 3 replications where the main plots were five ecotypes and subplots were the levels of salinity. Because of lack of space and facilities only one un-replicated row comprising all ecotypes was used as untreated for comparison with treated plants. The seeds were planted in plastic pots filled with sand and immersed in nutrient solution. After more than 2 months when the plant became mature the EC of nutrient solution was increased gradually by adding sodium chloride. At every 15 days the EC increased by 3 dS/m, and the final EC was 18 dS/m. The electrical conductivity at each stage of salt addition was 6, 12, and 18 dS/m. At each stage of salinity the physiological characteristics of alfalfa ecotypes were measured including: crop growth ratio, photosynthesis rate, chlorophyll content, stomatal conductance, chlorophyll fluorescence. The results showed that the physiological parameters were affected by salt concentration and there were varying responses between genotypes. Salt stress resulted in a linear decline in the photosynthetic rate from 21μmol/m2/s in control to 5μmol/m2/s at 18 dS/m. Ecotypes showed similar responses in photosynthesis and stomatal conductance under salt stress. A positive correlation between CO2 net uptake and stomatal conductance was observed. The chlorophyll content decreased with increasing salinity and there is a significant difference between ecotypes in terms of chlorophyll content. The results of Fv/Fm, ratio showed that up to 12 dS/m there was not significant changing in trend of Fv/Fm ratio but after 12 dS/m the Fv/Fm ratio decreased with increasing of salt stress. There was a significant difference in Fv/Fm ratio among the ecotypes with increasing salinity. The study indicated that physiological parameter relative to levels of salinity and ecotypes responses have been varying. In terms of physiological response to salt stress ecotype Ghargholough identified as most tolerant ecotype, so that it should be considered as a proper source for adapt in areas with impaction of climate change due to salt stress.