Leaf chlorophyll content is an important index for plant N status, photosynthesis capacity, and stress tolerance (Taiz et al., 2015). It is common to estimate leaf chlorophyll content using nondestructive optical chlorophyll meters (Ferrarezi et al., 2020; Neilsen et al., 1995). Relative chlorophyll content is estimated using the ratio of transmitted red light and NIR light emitted by a red and an NIR LED, respectively, through a leaf (Monje and Bugbee, 1992). Transmitted red light through a leaf is related inversely to the chlorophyll content because chlorophylls absorb red light efficiently (Taiz et al., 2015). Conversely, chlorophylls absorb little NIR light, thus NIR light can be used as a reference for a nonchlorophyll absorption spectrum (Monje and Bugbee, 1992). The SPAD-502 chlorophyll meter developed by Konica Minolta (Tokyo, Japan) is commercially available to estimate relative chlorophyll content. Recently, multiple chlorophyll meters such as the CL-01 chlorophyll content meter (Hansatech Instruments, Hitchin, UK), the Dualex leafclip sensor (Force-A, Paris, France), and the MC-100 chlorophyll meter (Apogee Instruments, Logan, UT) have been developed following a similar protocol (Kalaji et al., 2017).
Optical chlorophyll meters are simple, quick, and nondestructive tools for determining chlorophyll content (Parry et al., 2014), but efforts have been made to develop alternative options because of their high prices (Richardson et al., 2002; Vesali et al., 2015; Yang et al., 2003). NDVI sensors equipped with red and NIR light detectors are mostly used in remote sensing to estimate vegetation coverage (Wang et al., 2012). NDVI sensors are sensitive to the red and NIR light of solar radiation and may be used to estimate leaf chlorophyll content through determining transmitted red and NIR light to help growers adjust fertilization.
In our study, an NDVI sensor (S2-412-SS, Apogee Instruments) and two commercial chlorophyll meters (MC-100 and SPAD-502) were used to measure leaf chlorophyll content of ‘Torrey’ buffaloberry (Shepherdia × utahensis). Chlorophyll extraction was also conducted to assess the accuracy of estimating leaf chlorophyll content using NDVI sensors. Because sunlight varies greatly depending on weather and seasonality, one concern about using NDVI sensors to estimate chlorophyll content is if changes in solar radiation affect the chlorophyll content measurements. The impacts of sunlight and electric light source (e.g., halogen) on NDVI measurements were compared.
Chen, J., Kratsch, H., Norton, J., Sun, Y. & Rupp, L. 2020 Nodulation and plant growth of Shepherdia ×utahensis ‘Torrey’ topdressed with controlled-release fertilizer HortScience 55 1956 1962
Ferrarezi, R., Geiger, T.C., Greenidge, J., Dennery, S., Weiss, S.A. & Vieira, G.S. 2020 Microirrigation equipment for okra cultivation in the U.S. Virgin Islands HortScience 55 1045 1052
Kalaji, H.M., Dąbrowski, P., Cetner, M.D., Samborska, I.A., Łukasik, I., Brestic, M., Zivcak, M., Tomasz, H., Mojski, J., Kociel, H. & Panchal, B.M. 2017 A comparison between different chlorophyll content meters under nutrient deficiency conditions J. Plant Nutr. 40 1024 1034
Kusuma, P. & Bugbee, B. 2021 Far-red fraction: An improved metric for characterizing phytochrome effects on morphology J. Amer. Soc. Hort. Sci. 146 3 13
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