Effect of Aluminum Stress on Photosynthetic Characteristics and Chlorophyll Fluorescence Parameters of Watermelon Seedlings

In the study,two watermelon varieties Zaomiwang( ZM) and Zaochunhongyu( HY) seedlings were used as materials to investigate the effect of aluminum( Al) on growth and physiological characteristics under different Al concentrations( 0,250,500,1 000,1 500 μmol / L) treatment in order to find out the impact of aluminum stress on photosynthetic characteristics of watermelon. Changes in root length and biomass results showed that ZM was more sensitive to Al than HY. Effects on photosynthesis for the followed three aspects: Chlorophyll content of HY increased in the Al treatment. Chlorophyll content of ZM was higher than contrast only when Al concentration was 250 μmol / L. Chlorophyll a / b content of HY intended to decrease as long as the Al concentration increased; In the Al treatment,when concentration lower than 500 μmol / L the stomatal conductance( Gs),intercellular CO2concentration( Ci),net photosynthetic rate( Pn) and transpiration rate( Tr) of ZM was effected more obviously than those of HY. When Al concentration was above 1 000 μmol / L,the value of these four items all intended to fall down; Changes of Chlorophyll fluorescence in these two watermelon variety in the Al treatment( without Al3 += 250μmol /L concentration) were as follow: original fluorescence( Fo),maximum fluorescence( Fm),potential photochemical efficiency( Fv / Fo),photochemical maximum efficiency of PS Ⅱ( Fv / Fm) and the ability of leaves to transform energy Y( Ⅱ) decreased,while non-photochemical quenching( NPQ) increased,and leaves maintained a high actinic light energy distribution by adjusting the heat dissipation; In addition,photochemical quenching coefficient( q P) and electron transport rate( ETR) decreased. At Al3 +≤250 μmol/L concentration,the four parametersof HY: Fo,Fm,Fv / Fo,Fv / Fm was more stable; with aluminum concentration increases,the electron transfer rate was less affected,NPQ relatively constant,that is able to maintain a constant light protection.