Abstract
BackgroundIn plants, three-dimensional (3-D) organs such as inflorescences or fruits carry out photosynthesis and thus play a significant role in carbon assimilation and yield. However, this contribution has been poorly characterized because there is no reliable method for measuring photosynthesis by 3-D organs. One of the major challenges is ensuring the uniform irradiation of samples that are placed within a sealed chamber.ResultsIn this study, we developed an innovative chamber with homogeneous lighting that can be used to measure photosynthesis by large 3-D organs. It consisted of a 15-cm-long sealed transparent cylinder that was surrounded by a decagonal prismatic light source, made up of a mixture of red and blue LEDs. We characterized irradiance homogeneity within the chamber at a resolution level of 1 cm and 10°. Photosynthetic photon flux density (PPFD) along the central axis of the chamber could be set to any value between 100 and 1100 µmol m−2 s−1. The coefficient of variation for the irradiation values found throughout the chamber was 10% and that for the ratio of red-to-blue spectra was less than 1.5%. The temperature of the sample was regulated to stay within 1 °C of the target temperature, regardless of PPFD. We compared the performance of our device with that of a commercially available device employing unidirectional lighting. Specifically, we examined net photosynthesis in two sample types—wheat ears and grape clusters—at varying PPFD levels.ConclusionsThe devices gave similar estimates of dark respiration, regardless of sample type or age. Conversely, net photosynthesis started to become asymptotic at lower irradiance levels in our device than in the conventional device because apparent quantum yield was three times higher. When examining the effects of irradiance heterogeneity, it was clear that biased estimates could result from systems employing unidirectional light sources. Our results also confirmed that our chamber could be a useful tool for obtaining more accurate estimates of photosynthesis by 3-D organs.
Highlights
In plants, three-dimensional (3-D) organs such as inflorescences or fruits carry out photosynthesis and play a significant role in carbon assimilation and yield
The quantum sensor placed in the center of the chamber indicated that Photosynthetic photon flux density (PPFD) was linearly correlated with input voltage
There was a small offset since the Light emitting diode (LED) turned on at values above 1.10 VDC and turned off at values below 0.95 VDC
Summary
Three-dimensional (3-D) organs such as inflorescences or fruits carry out photosynthesis and play a significant role in carbon assimilation and yield. This contribution has been poorly characterized because there is no reliable method for measuring photosynthesis by 3-D organs. Most wholeplant and crop models are based on photosynthesis by laminas, as that of Farquhar et al [2], even though the contributions of other photosynthetic organs, as the stem [3, 4] and fruits [5], have largely been recognized. At a time when this parameter becomes a phenotyping criterion, such an approximation can mask varietal behaviors of interest and make selection difficult
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