Spatiotemporally variable incident light, leaf photosynthesis, and yield across a greenhouse: fine-scale hemispherical photography and a photosynthesis model

Abstract

Although greenhouse agriculture can generate high crop yields, they vary due to spatiotemporal differences in incident light and photosynthesis. To elucidate these dynamics, multipoint analysis of hemispheric images and a photosynthesis model were used to visualize the spatiotemporal distribution of photosynthetic photon flux density (PPFD) and leaf photosynthetic rate (A) and compared these with strawberry fruit yield in a greenhouse. This method enabled successful estimation of spatiotemporal variability in PPFD and A with relative root mean square errors of 4.4% and 11.0%, respectively. PPFD, captured at ca. 2 m resolution, varied diurnally and seasonally based on sun position and external light intensity. A showed less spatial variability, because it is reduced by physical and physiological mechanisms in the leaves at excessive leaf temperatures and becomes saturated at high PPFD. Yield spatial variability was better explained by A than by PPFD. The association between A and yield weakened over the cultivation period (R2 declined from 46% in winter to 12% in spring), thus suggesting that, over the cultivation period, factors such as photoassimilate availability replaced A as the primary limiting factor. The proposed method can be directly applied to other types of greenhouses, and the findings may facilitate spatiotemporal optimization in crop production, improving precision greenhouse agriculture.