Diurnal Variation in Root Respiration

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Abstract
A diurnal variation in root respiration was observed with intact root systems of 3 species of plants grown in the greenhouse in nutrient culture. Respiratory rates during daylight were 25-50% greater than during the night. The diurnal variation occurred under conditions of constant temperature and humidity. When light was also held constant, the variation pattern was interrupted, although root respiration still fluctuated. There also was a diurnal variation in uptake of Rb86 by intact plants with maximum rates during the day. On the other hand, with respiration and ion accumulation of tissue excised from root systems at various periods of the day and night there was no significant diurnal fluctuation. Thus the shoot proved essential for the development of the diurnal variation in root activities. Sugar analyses showed that the fluctuations in root respiration were not correlated with substrate levels.