Analysis of Bell Pepper (Capsicum annuum L.) Leaf Spectral Properties and Photosynthesis According to Growth Period

This study analyzed the leaf spectral properties and photosynthesis rates of greenhouse-grown bell pepper leaves according to the growth period and leaf position to investigate the changes in carbon assimilation function according to leaf aging. Photosynthesis, growth, transpiration, stomatal conductance, light transmittance, and light reflectance were measured. As the plants’ growth progressed, the number of leaves, fresh weight, and dry weight increased, but the specific leaf area decreased, likely due to the increased distribution of assimilates to reproductive organs. The average photosynthesis rate, according to the measured dates, exhibited a high value despite a large standard error, which was likely influenced by measurement errors caused by external environmental factors. The reflectance and transmittance increased from the upper to the middle and bottom leaves, and the absorption ratio decreased in the same order. The green light spectrum (500–580 nm) had a lower absorption ratio than other spectra because the green coloration of the leaves increased the light reflectance of this spectrum. As the PPFD increased where the leaf was positioned higher, the photosynthesis rate, transpiration amount, and stomatal conductance also increased. The higher the leaf position, the higher the photosynthesis rate, the amount of transpiration, and the stomatal conductance. As the CO2 concentration increased, the photosynthesis rate increased, but the transpiration and stomatal conductance changed little, indicating that the gas exchange within leaves was hardly affected by CO2, but the light levels promoted photosynthesis. From the results of this study, the optical properties of the leaves indicate that they are consistent with Lambert–Beer’s law, which implies that the length of the optical path is linearly proportional to the number of molecules in the absorption layer. We obtained the light saturation point and CO2 saturation point of bell peppers grown in a greenhouse and were able to determine the physiological changes in the leaves with increasing leaf age. Therefore, based on this information, it appears that a leaf removal model based on the productivity of bell pepper leaves could be developed.