Effect of temporally heterogeneous light on photosynthetic light use efficiency, plant acclimation and growth in Abatia parviflora

Abstract

Individual leaves have a unique instantaneous photosynthetic photon flux density (PPFD) at which net photosynthetic light use efficiency (?L, the ratio between net photosynthesis and PPFD) is maximised (PPFD?max). When PPFD is above or below PPFD?max, efficiency declines. Thus, we hypothesised that heterogeneous PPFD conditions should increase the amount of time leaves photosynthesise at a PPFD different than PPFD?max and result in reduced growth. To date, this prediction has not been rigorously tested. Here, we exposed seedlings of Abatia parviflora Ruiz and amp; Pav to light regimes of equal total daily irradiance but with three different daily time courses of PPFD: constant PPFD (NoH), low heterogeneity (Low-H) and high heterogeneity (High-H). Mean ?L, leaf daily photosynthesis and plant growth were all significantly higher in No-H and Low-H plants than in High-H plants, supporting our hypothesis. In addition, mean ?L was positively related to final plant biomass. Unexpectedly, High-H plants had more etiolated stems and more horizontal leaves than No-H and Low-H plants, possibly due to exposure to low PPFD in the morning and afternoon. In conclusion, PPFD heterogeneity had an important effect on average ?L, photosynthesis and growth, but also on allocation and plant morphology. © 2019 CSIRO.