EFFECT OF INCREASING ROOT-ZONE TEMPERATURE ON GROWTH AND NUTRIENT-UPTAKE BY GOLD-STAR MUSKMELON PLANTS

Growth response of plants to root-zone temperature (RZT) varies with s pecies. We studied the effects of RZT on muskmelons (Cucumis melo L. ' Gold Star') held continuously at 25 degrees, 30 degrees, 35 degrees, 4 0 degrees, and 45 degrees C in a nutrient solution bath for 12 days. M uskmelon seedling sizes used were the first and fourth leaf growth sta ges. Large seedling size growth rate was approximately double that of the small size. Plant fresh weight gain for large plants was highest a t the 25 degrees C RZT, while for small plants fresh weight gain was s imilar from 25 to 35 degrees C. But dry weight gain was similar for bo th plant sizes from 25 to 35 degrees C. Root-zone temperatures >35 deg rees C resulted in a sharp linear decrease in fresh weight, dry weight , and leaf number. Shoot elemental phosphorus (P), zinc (Zn), and mang anese (Mn) content and concentration followed the same pattern as grow th. Root P and Zn concentration increased linearly with increasing RZT , but Mn concentration reached a maximum at 35 degrees C. The RZT thre shold for optimum muskmelon seedling growth seems to be 35 to 36 degre es C.