Abstract
Diurnal and day-to-day fluctuations in the concentrations of mineral nutrients in the leaves of spinach were investigated by successive sampling of the pot-grown plants.
1. As for diurnal fluctuations, the concentrations of N, P, K and Mg on a dry weight basis decreased after sunrise and reached a minimum in the late afternoon. They increased thereafter and reached a maximum at dawn.
2. The concentrations of N and Mg as % fresh weight and of K as % tissue water increased in the daytime and decreased at night.
3. Regarding day-to-day fluctuations, the concentrations of P and K as % dry weight continued to decrease over 3 days immediately after rainy days in the leaves sampled either at dawn or in the afternoon.
4. The concentrations of N, Ca and Mg as % fresh weight and of K as % tissue water were constant in the leaves sampled at dawn, except on the day immediately after rainy days. In the leaves sampled in the afternoon, those were constant even after rainy days.
5. After the number of leaves ceased to increase due to low temperature, the concentrations of N, P and K as % dry weight decreased but those of N, Ca and Mg as % fresh weight and that of K as % tissue water increased.
6. No diurnal nor day-to-day fluctuations were found in the concentration of P on a fresh weight basis.
