The Quantity of Aluminum and Phosphorus in Plants and Its Influence on the Sepal Color of <i>Hydrangea macrophylla</i> DC

The quantity of aluminum and phosphorus contained in Hydrangea macrophylla DC. changes from the raising period to the flowering time. The present investigation was undertaken to make clear the feature of this change and its influence on sepal color, using the scarlet-flowered cultivars ‘King George’ and ‘Prima’.<br>During the raising period from June to December prior to forcing, the potted plants were grown in acid soil of pH5.7, prepared by mixing equal parts of red loam (Kanto-loam) and well-decayed manure. The considerable amounts of aluminum and phosphorus were absorbed and accumulated during this raising period, but the large portion of them, i.e. 70-80 per cent of total amount was lost through the defoliation in late fall. On December 12, the amount of aluminum in ‘King George’ and ‘Prima’ was no more than 0.55mg and 0.707mg per plant, respectively.<br>On December 25, the plants were divided into two different soil plots. One plot was repotted with the acid soil of pH6.05 similarly prepared to the soil previously used and the other with the alkline soil of pH7.50 prepared by addition of calcium hydroxide to the sandy loam soil. All pots were then transferred to a greenhouse and forced at the temperature of 15-25°C until flowering.<br>The sepal color of plants grown in the alkaline soil during the forcing period was clear scarlet, while the color of these in the acid soil was dark blue or mauve. Absorption maxima of spectra of the blue sepals were 557mμ in ‘King George’ and 582mμ in ‘Prima’, whereas those of the scarlet sepals were 532mμ and 540mμ, respectively. Moreover, the distribution of spots of the scarlet sepals on Hunter′s color diagram was clearly separated from those of the blue sepal.<br>The concentration of aluminum in each plant part, in particular in flower part of those grown in the acid soil, was much higher than that in the alkaline soil. The values of the former were 985ppm and 1, 258ppm, and those of the latter were 430 ppm and 335ppm for each variety. By contrast, the concentration of phosphorus absorbed was inversely correlated. It was much lower in the acid soil plot as compared with alkaline soil plot. The ratios of the concentration of aluminum to phosphorus of ‘King George’ and ‘Prima’ in the acid soil were 0.334 and 0.434, whereas those in the alkaline soil were only 0.106 and 0.094 respectively.<br>Furthermore, the concentration of water soluble aluminum in plants, which plays presumably an important role for the formation of the blue aluminum-anthocyanin complex, was much higher in plant of the acid soil plot than in the alkaline soil. The percentages of it to total aluminum in flower part were 27-38 per cent in the acid soil and only 7-8 per cent in the alkaline soil.<br>On the basis of these evidences it was considered that, within plants, some of aluminum absorbed is combined with phosphorous and turns into insoluble compound and, in addition to this change, the much less absorption of aluminum in the alkaline soil may prevent the formation of blue aluminum-anthocyanin complex, thus leading to the clear scarlet color.