Chlorophyll fluorescence parameter of F_v/F_m, as an important index for evaluating crop yields and biomass, is key to guide crop management. However, the shortage of good hyperspectral data can hinder the accurate assessment of wheat F_v/F_m. In this research, the relationships between wheat canopy F_v/F_m and in-situ hyperspectral vegetation indexes were explored to develop a strategy for accurate F_v/F_m assessment. F_v/F_m had the highest coefficients with normalized pigments chlorophyll ratio index (NPCI) and the medium terrestrial chlorophyll index (MTCI). Both NPCI and MTCI were increased with the increase in F_v/F_m. However, NPCI value ceased to increase as F_v/F_m reached 0.61. MTCI had a descending trend when F_v/F_m value was higher than 0.61. A piecewise F_v/F_m assessment model with NPCI and MTCI regression variables was established when F_v/F_m value was ≤0.61 and >0.61, respectively. The model increased the accuracy of assessment by up to 16% as compared with the F_v/F_m assessment model based on a single vegetation index. Our study indicated that it was feasible to apply NPCI and MTCI to assess wheat F_v/F_m and to establish a piecewise F_v/F_m assessment model that can overcome the limitations from vegetation index saturation under high F_v/F_m value.

Dun-Liang Wang

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