Effects of different irrigation minima on the growth and physiological characteristics of lettuce under plastic greenhouse

The effects of different field water capacities(70%～90%, 60%～90%, 50%～90%, 40%～90%) on the yield, quality, chlorophyll fluorescence parameters and protective enzymes of lettuce were investigated. The results show that the greatest shoot fresh weight, leaf water content, leaf area and leaf number were obtained by 70% irrigation minimum treatment. Soluble sugar and soluble protein of lettuce gradually increased with the decrease of irrigation minima, whereas the highest content of vitamin C was obtained by 50% irrigation minima. Fv/Fm, qP, ΦPSⅡ decreased whereas qN increased with the decrease of irrigation minima. The activities of SOD and CAT and the contents of MDA and Pro increased with the decrease of irrigation minima. The highest yield was obtained by 70% irrigation minimum treatment, whereas the best irrigation minimum was 60% for the growth and quality of lettuce.