Recent levels of daily photosynthetic photon flux density have a larger influence on light acclimation responses of cucumber leaves than earlier levels

Leaves respond to the photosynthetic photon flux density (PPFD) and accordingly adjust their morphological and physiological properties, including leaf mass per area (LMA) and the chlorophyll (chl) a/b ratio. These responses are called light acclimation responses. Although the properties that are responsive to high or low constant PPFD levels have been well described, the extent of the responses to changing PPFD, as observed in open fields and greenhouses, remains insufficiently quantified. In this study, we quantitatively investigated the effects of changes among three PPFD levels (100, 400, and 700 μmol m −2 s −1 ) over six days (constant within each day) on leaf light acclimation responses in cucumber ( Cucumis sativus ) seedlings. We introduced a time-weighted average PPFD ( L w ), in which the effect of the PPFD in the earlier growth period was given less weight, and demonstrated a significant linear regression of parameters of the leaf light acclimation responses including the LMA, chl a / b ratio, maximum rate of carboxylation capacity of ribulose-1,5-bisphosphate carboxylase/oxygenase ( V c max ) and maximum rate of electron transport ( J max ) on L w . The result showed that the linear regression model with L w well explained the light acclimation responses of leaves to the day-to-day changes in daily PPFD and it estimated these response parameters more accurately than a model with an average PPFD.