Plant water parameters and the remote sensing R 1300/R 1450 leaf water index: controlled condition dynamics during the development of water deficit stress

Plants with different abilities for osmotic adjustment (cowpea, bean, and sugarbeet) were subjected to gradually decreasing soil water content. During the development of water deficit stress, various plant water parameters were measured to characterize their relationship to the near infrared R (1300)/R (1450) leaf water index, which is based on the measurement of light reflected from leaves. In all three species, leaf water thickness (LWT), leaf cell relative water content (RWC), and overall leaf thickness remained relatively constant under moderate water deficit stress. However, at the point when plants could no longer cope with the increasing level of water deficit stress, LWT, RWC, and leaf thickness were found to decrease substantially, signaling the onset of leaf dehydration. The R (1300)/R (1450) leaf water index followed the RWC very closely in cowpea and bean leaves, and with some time lag in sugarbeet leaves. The R (1300)/R (1450) index may therefore be used as a feedback-signal in precision irrigation control, signaling effectively the physiological response of plants when water deficit stress becomes detrimental. RWC and the R (1300)/R (1450) index were linearly correlated in cowpea and bean leaves, but not in sugarbeet leaves.