Chlorophyll fluorescence upper-to-lower-leaf ratio for determination of irrigation time for Pentas lanceolata

摘要

The objective of this study was to use nondestructive measurements as the precise irrigation indices for potted star cluster (Pentas lanceolata). Drought stress was imposed on plants for 0, 3, 5, 7, 12, and 16 d by withholding water. Measurements were conducted on the third leaf counted from the apex (upper leaves) and on the third leaf from the bottom (lower leaves). Within the range of soil water content (SWC) from 10 to 45%, leaf water potential (WP), SWC, and soil matric potential (SMP), chlorophyll fluorescence, photochemical reflectance index (PRI), adjusted normalized difference vegetation index (aNDVI), and the reflectance (R) at 1950 nm (R-1950) were measured. The plants reached the temporary wilting point at -3.87 MPa of leaf WP; the maximal fluorescence yield of the light-adapted state (F-m') ratio of upper-to-lower leaves was 1.7. When the F-m' ratio was 1.3, it corresponded to lower-leaf WP -2.27 MPa, SWC 21%, SMP -20 kPa, PRI 0.0443, aNDVI 0.0301, and R-1950 > 8.904; it was the time to irrigate. In conclusion, the F-m' ratio of upper-to-lower leaves was shown to be a nondestructive predictor of leaf WP and can be used to estimate irrigation timing.