Can SPAD Values and CIE L*a*b* Scales Predict Chlorophyll and Carotenoid Concentrations in Leaves and Diagnose the Growth Potential of Trees? An Empirical Study of Four Tree Species

Photosynthetic pigments are fundamental for plant photosynthesis and play an important role in plant growth. Currently, the frequently used method for measuring photosynthetic pigments is spectrophotometry. Additionally, the SPAD-502 chlorophyll meter, with its advantages of easy operation and non-destructive testing, has been widely applied in land agriculture. However, the application prospects of its test results in horticultural plants have not yet been proven. This study examines the reliability of SPAD values for predicting chlorophyll concentrations. Using fresh and senescent leaves from four common horticultural plants, we measured SPAD values, photosynthetic pigment concentrations, and leaf color parameters. A generalized linear mixed model demonstrated that SPAD values are a reliable indicator for predicting chlorophyll concentrations, yet interspecific variations exist. Based on the predictive power of SPAD values for chlorophyll, we first propose an Enrichment Index (CEI) and a Normal Chlorophyll Concentration Threshold (NCCT). The CEI can be used to compare SPAD values among different species, and the NCCT value can serve as a more accurate indicator for assessing the growth potential of old trees. However, due to a limited sample size, further research with larger samples is needed to refine the diagnosis of plant growth potential and enhance the management of ornamental plant cultivation.