SEQUENTIAL EFFECTS OF CARBOHYDRATE ACCUMULATION AND CONSUMPTION IN MARIGOLD SEEDLINGS

Abstract

Supplemental CO2 of 1500 μl/l with radiation of 35 mols/day/m2 resulted in a daily net accumulation of 60% increase in starch and 100% increase in soluble sugars at the end of the light period compared to seedlings grown at ambient CO2. During low solar radiation periods the net daily accumulation of starch and soluble sugars was very little in seedlings grown with or without supplemental CO2. At night, the concentration of starch decreased linearly with time, whereas soluble sugars decreased only slightly. The greater the concentration of carbohydrates at sunset the greater the metabolism of carbohydrates at night. When solar radiation was between 30-60 mols/day/m2, the greater the concentration of starch in seedlings at the end of the dark period the lower the net daily accumulated starch at the end of the next day. Also higher night temperatures (23° vs. 8°), which maintained high metabolism of starch at night and thus a lower starch concentration at sunrise the next day, was correlated with greater net accumulated starch at the end of the next day. These results indicate that starch may inhibit photosynthesis in marigold seedlings; thus cultural practices that maintain low starch accumulation or high metabolism may enhance photosynthesis.