Assessing shaded-leaf effects on photochemical reflectance index (PRI) for water stress detection in winter wheat
The photochemical reflectance index (PRI) has emerged to
be a pre-visual indicator of water stress. However, whether the varying
shaded-leaf fractions, which may be caused by multiple view angles or the
changing crop density in the field, affect the performance of PRI in
detecting water stress of crops is still uncertain. This study evaluated the
impact of the varying shaded-leaf fractions on estimating relative water
content (RWC) across growth stages of winter wheat using seven formulations
of PRI. Results demonstrated that for the control treatment the mean PRI of
sunlit leaves was slightly higher than those of shaded leaves, but the
difference between PRI of sunlit and shaded leaves increased as water
resources became more limiting. Despite the difference between PRI of sunlit
and shaded leaves, the significance of the linear relationship between RWC
and most studied formulations of PRI did not show obvious variations with
shadow fractions, except for the 100 % shaded-leaf condition. Among the
studied formulations of PRI, PRI3 based on reflectance at 512 nm as the
reference band provided the most accurate estimates of RWC with varying
shaded-leaf fractions, except for the 100 % shaded-leaf condition. The
slope and the intercept of linear regression models with PRI3 also showed
minimized variations with shaded-leaf fractions. We then applied a uniform
RWC prediction model to the data of varying shaded-leaf fractions and found
that the accuracy of RWC predictions was not significantly affected in the
mixture of sunlit and shaded leaves. However, RWC estimated with PRI of the
100 % shaded-leaf condition had the highest root mean square error (RMSE), implying that PRI of the
pure shaded leaves may yield inaccurate estimates of plant water status.
Vorschau
Zitieren
Yang