1974 Volume 43 Issue 1 Pages 15-23
Diurnal and seasonal fluctuations in osmotic concentration in leaves and shoots of alternate- and annual-bearing satsuma mandarin trees were examined to test whether or not these changes are correlated to the internal moisture status. The following observations were made:
1) Osmotic values of leaves and shoots increased during the day attaining a maximum about 2-4PM and subsequently decreased to a minimum at 6AM. This diurnal pattern did not vary among the different seasons. Analysis of seasonal samples taken once a month at 10AM revealed that the osmotic values were relatively low in mid-summer and high during the months of January and February. The osmotic values increased beyond the degree of the decrease in water contents in winter. It was also confirmed from these data that the change of osmotic values in winter was due not only to that of the water contents but also to that of the solute ratios.
2) Calculations of the solute ratio by the following equation:
Solute ratio=osmotic value (atm)×% moisture content/24.05, the constant 24.05=the osmotic value of a molal solution, disclosed that the values of leaves and shoots closely paralleled the water contents in the organs from spring to summer and corresponded to osmotic concentrations of them from autumn to winter. Changes in solute ratios of leaves and stems occasionally oscillated as much as I mol which was comparable to the maximum amplitude of their diurnal fluctuations found in the organs.
3) The presence of fruits influenced the osmotic values of the sap extracted from leaves and shoots. The osmotic values of leaves and stems in non-bearing 4-year-old trees were respectively higher in almost every season as compared to those of correspondingly aged organs in the bearing trees.
4) As for alternate bearing mature trees in the on-year, osmotic concentration of 1-year-old leaves was relatively low during the period from June to September, increasing markedly after harvest. From autumn to winter, however, two-year-old leaves and shoots of heavily cropped trees did not show an increase in osmotic concentration which comparable organs from trees with a light or no crop manifested at the same period.
