Diurnal Response of Sun-Induced Fluorescence and PRI to Water Stress in Maize Using a Near-Surface Remote Sensing Platform

Abstract

Sun-induced Fluorescence (SIF) and Photochemical Reflectance Index (PRI) data were collected in the field over maize to study their diurnal responses to different water stresses at the canopy scale. An automated field spectroscopy system was used to obtain continuous and long-term measurements of maize canopy in four field plots with different irrigation treatments. This system collects visible to near-infrared spectra with a spectrometer, which provides a sub-nanometer spectral resolution in the spectral range of 480~850 nm. The red SIF (FR) and far red SIF (FFR) data were retrieved by Spectral Fitting Methods (SFM) in the O 2 -A band and O 2 -B band, respectively. In addition to PRI, Δ PRI values were derived from PRI by subtracting an early morning PRI value. Photosynthetic active radiation (PAR) data, the canopy fraction of absorbed PAR (fPAR), and the air/canopy temperature and photosystem II operating efficiency (YII) at the leaf scale were collected concurrently. In this paper, the diurnal dynamics of each parameter before and after watering at the jointing stage were compared. The results showed that (i) both FR and FFR decreased under water stress, but FR always peaked at noon, and the peak of FFR advanced with the increase in stress. Leaf folding and the increase in Non-photochemical Quenching (NPQ) are the main reasons for this trend. Leaf YII gradually decreased from 8:00 to 14:00 and then recovered. In drought, leaf YII was smaller and decreased more rapidly. Therefore, the fluorescence yield at both the leaf and canopy scale responded to water stress. (ii) As good indicators of changes in NPQ, diurnal PRI and Δ PRI data also showed specific decreases due to water stress. Δ PRI can eliminate the impact of canopy structure. Under water stress, Δ PRI decreased rapidly from 8:00 to 13:00, and the maximum range of this decrease was approximately 0.05. After 13:00, their values started to increase but could not recover to their morning level. (iii) Higher canopy-air temperature differences ( Δ T ) indicate that stomatal closure leads to an increase in leaf temperature, which maintains a higher state in the afternoon. In summary, to cope with water stress, both leaf folding and changes in physiology are activated. To monitor drought, SIF performs best around midday, and PRI is better after noon.

Nonlinear Relationship Between the Yield of Solar-Induced Chlorophyll Fluorescence and Photosynthetic Efficiency in Senescent Crops

“…Numerous studies have found that the leaf F q /F m is linearly related to the canopy SIF based on ground measurements [17,18]. This linear relationship is the scientific basis for the application of SIF in detecting the gross primary productivity (GPP) at various ecosystem levels, because SIF and GPP can be separately calculated as: SIF = SIF yield × APAR and GPP = PSII operating efficiencey × APAR.…”

“…Thus, the linear relationship between SIF and GPP is briefly determined by the ratio LUE P /LUE F (λ). A mass of evidence based on experimental measurements has shown that the relationship between LUE P and LUE F (λ) (i.e., the SIF yield at 760 nm) is linear [17,18], which means that the value of LUE P /LUE F (λ) remains relatively constant and GPP is linearly related to SIF in a specific ecosystem.…”

Retrieving the Diurnal FPAR of a Maize Canopy from the Jointing Stage to the Tasseling Stage with Vegetation Indices under Different Water Stresses and Light Conditions

“…In reference to previous research [ 13 , 24 , 31 , 32 , 33 , 34 ], based on the characteristics of this study and combined with the physical meaning of the VI, we evaluated 13 VIs ( Table 1 ) in relation to the canopy structure, chlorophyll, soil adjustment, and physiological response to stress. We also selected some red-edge VIs that had a good estimate effect for the FPAR, according to Dong et al (2015) [ 31 ].…”

“…These results show that instantaneous NDVI measurements provide a stable and near-linear estimate of the diurnally integrated FPAR in an herbaceous vegetation canopy as long as the remotely sensed observations are taken when the solar zenith angle is above 60° and the sensor views are within 40° of the nadir [ 14 ]. Recent in situ measurements, however, show that the FPAR may fluctuate dramatically within a day because of changes in the light conditions [ 23 ] and stress states [ 24 ]. The FPAR diurnal course of an alpine wetland showed a “bowl-shaped” pattern, which was small around noon but larger in the early morning (before 10:00) and mid-afternoon (after 14:00) [ 23 ].…”

“…The FPAR diurnal course of an alpine wetland showed a “bowl-shaped” pattern, which was small around noon but larger in the early morning (before 10:00) and mid-afternoon (after 14:00) [ 23 ]. Under a water deficit, the decline of the FPAR around noon will become much more significant [ 24 ].…”