Diel changes in tuber volume

Summary The long-term and short-term changes in volume of tubers from plants grown under controlled conditions, when assessed by an accurate, non-destructive tuber-volume meter, showed sigmoid increases in volume. The diel changes were remarkable: the rate of volume increase was very high shortly after the onset of the dark phase, but it declined sharply directly after the onset of the light phase; it was much faster during the night than during the day, especially in the later stages of growth. The nocturnal rate of volume increase was greatest when the tubers showed their greatest overall rate of growth. The daytime increases in volume were fastest during the early stages of tuber development. The key process underlying these phenomena seems to be the movement of water out of and into the tuber.