Effect of irradiance and temperature on composition of spinach

The Connecticut Agricultural Experiment Station studied the composition of spinach (Spinacea oleracea L.) in response to daily light integral (DLI) and diurnal variation in a greenhouse. Values for plantings with different irradiance were compared using normalized daily light integral (NDLI), which was DLI divided by leaf area index.

The dry mass as a ratio of fresh mass increased with NDLI as it increased from 3 to 27 mol·m−2·d−1. Reduced nitrogen (N) changed with time of day under high but not under low NDLI. Nitrate and amino acids were affected by temperature more than NDLI. Starch increased with NDLI to 27 mol·m−2·d−1 in morning or afternoon. However, sugars decreased with temperature more than with NDLI, due to a decrease in petioles up to 20 °C. Oxalic acid increased with NDLI or temperature.

Over a diurnal cycle, starch had minimum value at 0800 hr and maximum at 1800 hr in all parts. The sugars, sucrose, glucose, and fructose, had a binary response with high values in the day and low values in the night. Oxalic acid increased at the end of the day. Other metabolites had no response to time of day. The growth of spinach may be slow in fall compared with summer due to the effect of low temperature on metabolism of sugars and nitrate.

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