Effects of Salt Stress on Growth and Photosynthetic Traits of Canola Seedlings

A pot experiment was carriend out using canola in sand culture to explore effects of 10 and 30 days of NaCl strees(0、50、100、200、300 mmol·L^-1)on biomass,chlorophyll (Chl),net photosynthetic rate (P_n),stomatal conductivity (G_s),intercellular CO₂ concentration(x_i),transpiration rate (E_w,u)and stomatal limitation(L_s)of canola seedlings.Results show that NaCl stress decreased significantly plant dry weight,especially when the salt was high in concentration and existed for a long time;with increasing NaCl concentration,chlorophyll (Chl)content and Chl a/Chl b ratio both displayed a variation pattern of asceding first and descending later,and peaked under the strees of 200 mmol·L^-1NaCl,for 10 days and under the strees of 100 NaCl for 30 days.P_n,x_iand L_sin canola leaves growing under the stress of 50 and 100 mmol·L^-1NaCl strees were not much affected,but,P_n,G_s,x_i and R_twere markedly decreased when the stress was higher,however,in this case,E_w,uand L_s increased significantly.Correlation analysis indicated that biomass(dry weight)of canola was insignificantly related to Chl content and Chl a/Chl b ratio,but significantly and negatively related to Na⁺,Cl^- content,E_w,uand L_s,and significantly and positively related to root/shoot ration(R/S),K⁺,Ca²⁺content,K⁺/Na⁺,Ca²⁺/Na⁺ratio,K⁺and Na⁺selectivity ratioS(K⁺,Na⁺),Ca²⁺and Na⁺selectivity ratioS(Ca²⁺,Na⁺),P_n,G_s,x_iand R_t.The findings indicate that in seedings under the stress of 200 mmol·L^-1NaCl for 10 or 30 days,or 300 mmol·L^-1NaCl for 10 days,stomatal limitation was the major restraint of photosynthesis.But when the stress was increased to 300 mmol·L^-1NaCl for 30 days,both stomatal and nonstomatal limitations played important roles in restraining photosynthesis.Na⁺,Cl^-,K⁺and Ca²⁺contents,E_w,u, L_s,R/S,K⁺/Na⁺,Ca²⁺/Na⁺,S(K⁺,Na⁺),S(Ca²⁺,Na⁺),P_n,G_s,x_i and R_tcan all be regarded as indexes for evaluation of canola in salt adaptability.