Relations of remote sensing leaf water indices to leaf water thickness in cowpea, bean, and sugarbeet plants

Remote sensing leaf water indices depend on two variables: the relative water content (RWC) of leaf cells, which may serve as an indicator for water deficit stress in plants, and leaf thickness. The measurement of leaf water thickness (LWT) appears to be an experimental method that can be well correlated with leaf water indices. We studied how leaf water indices relate to the LWT in cowpea, bean, and sugarbeet. In all three species, the LWT increased linearly with increasing leaf thickness. The T1300/T1450 leaf water index, based on light transmitted through leaves, showed a strong exponential correlation with the LWT as expected from theoretical analysis. However, the R1300/R1450 leaf water index, based on light reflected from leaves, exhibited a characteristic logarithmic correlation with the LWT. For both leaf water indices we found only minor differences between the three species examined.