Calibration of a multi-species model for chlorophyll estimation in seedlings of Neotropical tree species using hand-held leaf absorbance meters and spectral reflectance

The aim of the present study was to calibrate a multi-species model for assessing leaf chlorophyll content in seedlings of six Neotropical rainforest tree species. Two hand-held chlorophyll absorbance meters (SPAD-502 and ClorofiLog) and the chlorophyll normalized difference leaf reflectance index (ND705) were tested. Measurements of leaf absorbance and reflectance, contents of chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll (Chl t), leaf area (LA), and leaf mass per area (LMA) were performed on fully expanded leaves. A total of 200 leaves were used for the calibration of the multiple-species model. The relative root mean square calibration errors (RMSεc, %) were calculated based on estimated chlorophyll values for multiple-species models and on measured values for each of the six species. The average values of LA varied between 14.2 and 29.5 cm-2, LMA between 34.8 and 98.9 g m-2, and Chl t between 3 and 815 mg m-2. For all indices, the highest values of the coefficients of determination (R2) were observed for Chl a (R2 ≥ 0.91), followed by Chl t (R2 ≥ 0.89) and Chl b (R2 ≥ 0.82). The highest values of R2 were obtained for ND705 (R2 ≥ 0.86) followed by SPAD-502 (R2 ≥ 0.83) and ClorofiLog (R2 ≥ 0.82). The present study showed that ClorofiLog and SPAD-502 indices could be safely interconverted by a simple linear regression model (R2 = 0.98). RMSεc values were lower than 20%, which confirmed the feasibility of the multi-species model for estimating the chlorophyll content using hand-held chlorophyll absorbance meters and leaf reflectance