Abstract
The purpose of this paper was to investigate the early water stress in maize using leaf-level measurements of chlorophyll fluorescence and temperature. In this study, a series of diurnal measurements, such as leaf chlorophyll fluorescence (Fs), leaf spectrum, temperature and photosynthetically active radiation (PAR), were conducted for maize during gradient watering and filled watering experiments. Fraunhofer Line Discriminator methods (FLD and 3FLD) were used to obtain fluorescence from leaves spectrum. This simulated work using the SCOPE model demonstrated the variations in fluorescence and temperature in stress levels expressed by different stress factors. In the field measurement, the gradient experiment revealed that chlorophyll fluorescence decreased for plants with water stress relative to well-water plants and Tleaf-Tair increased; the filled watering experiment stated that chlorophyll fluorescence of maize under water stress were similar to those of maize under well-watering condition. In addition, the relationships between the Fs, retrieved fluorescence, Tleaf-Tair and water content were analyzed. The Fs determination resulted to the best coefficients of determination for the normalized retrieved fluorescence FLD/PAR (R2 = 0.54), Tleaf-Tair (R2 = 0.48) and water content (R2 = 0.71). The normalized retrieved fluorescence yielded a good coefficient of determination for Tleaf-Tair (R2 = 0.48). This study demonstrated that chlorophyll fluorescence could reflect variations in the physiological states of plants during early water stress, and leaf temperature confirmed the chlorophyll fluorescence analysis results and improved the accuracy of the water stress detection.
Highlights
Vegetation water stress is a significant issue that currently affects maize growth and production.Maize is currently regarded as the most important food crop in the world
The meteorological data in Baoding, Hebei province, China, was used as input to derive the SCOPE model, and the results showed that the variations of some input parameters did not result in significant variations in fluorescence or temperature trends; these results are not presented here
Compared with fluorescence under different stress conditions, the extents of changes in fluorescence were relatively large around midday and small during the early morning and late afternoon
Summary
Vegetation water stress is a significant issue that currently affects maize growth and production.Maize is currently regarded as the most important food crop in the world. Numerous studies have shown that vegetation water stress can be measured using optical and thermal infrared remote sensing, as well as passive and active microwave remote sensing techniques [1,2,3,4,5,6,7,8,9,10]. These techniques exploit surface reflection, surface temperature, brightness, temperature and the backscatter coefficient separately to estimate soil moisture near the surface. Retrieving canopy component temperatures involve thermal infrared remote sensing problems, such as how to remove the effects of soil background [11], and the relationships between leaf temperature and water level are not clear [12]
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