The effect of potassium on translocation of photosynthates and yield pattern of potato plants

Abstract

The effect of increasing potassium supplies on the translocation of ¹⁴C‐labelled photosynthates from the leaves to the tubers was investigated in potatoes at different growth stages. Until flowering most of the assimilates were used for the development of above‐ground parts. With adequate K nutrition two thirds of the labelled photosynthates passed within one day into the tubers when after flowering intensive growth of tubers set in. With insufficient K supply (0.4 mequiv. K/litre), however, only half of the photosynthates were translocated to the tubers during the same period. The heavier accumulation of assimilates in the leaves resulted in a lower rate of photosynthesis in relation to leaf matter. It could thus be confirmed that potassium directly favours the transport of assimilates and, due to the faster translocation of photosynthates, brings about a higher assimilation rate of the leaves. The plants of the K₃ treatment (10 mequiv. K/litre) at all growth stages produced the highest tuber yield per leaf matter. On the other hand, the amount of leaf matter in these plants was smaller, so that the plants supplied with medium K rates (2.0 mequiv. K/litre) gave the highest absolute tuber yield. Within 24 hours three quarters of the labelled photosynthates were converted, for the major part into starch and protein. Potassium favoured in the young above‐ground parts the conversion of photosynthates to protein and in the tubers the synthesis of starch. Its effect on metabolism therefore differs in dependence on plant organ and physiological age of the plant.