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 species. We studied the effects of RZT on muskmelons (Cucumis melo L. 'Gold Star') held continuously at 25 degrees, 30 degrees, 35 degrees, 40 degrees, and 45 degrees C in a nutrient solution bath for 12 days. Muskmelon seedling sizes used were the first and fourth leaf growth stages. Large seedling size growth rate was approximately double that of the small size. Plant fresh weight gain for large plants was highest at the 25 degrees C RZT, while for small plants fresh weight gain was similar from 25 to 35 degrees C. But dry weight gain was similar for both plant sizes from 25 to 35 degrees C. Root-zone temperatures >35 degrees C resulted in a sharp linear decrease in fresh weight, dry weight, and leaf number. Shoot elemental phosphorus (P), zinc (Zn), and manganese (Mn) content and concentration followed the same pattern as growth. Root P and Zn concentration increased linearly with increasing RZT, but Mn concentration reached a maximum at 35 degrees C. The RZT threshold for optimum muskmelon seedling growth seems to be 35 to 36 degrees C.