Abstract
Measurement and analysis of the numerous reflectance indices of plants is an effective approach for the remote sensing of plant physiological processes in agriculture and ecological monitoring. A photochemical reflectance index (PRI) plays an important role in this kind of remote sensing because it can be related to early changes in photosynthetic processes under the action of stressors (excess light, changes in temperature, drought, etc.). In particular, we previously showed that light-induced changes in PRIs could be strongly related to the energy-dependent component of the non-photochemical quenching in photosystem II. The aim of the present work was to undertake comparative analysis of the efficiency of using light-induced changes in PRIs (ΔPRIs) based on different wavelengths for the estimation of the parameters of photosynthetic light reactions (including the parameters of photosystem I). Pea plants were used in the investigation; the photosynthetic parameters were measured using the pulse-amplitude-modulated (PAM) fluorometer Dual-PAM-100 and the intensities of the reflected light were measured using the spectrometer S100. The ΔPRIs were calculated as ΔPRI(band,570), where the band was 531 nm for the typical PRI and 515, 525, 535, 545, or 555 nm for modified PRIs; 570 nm was the reference wavelength for all PRIs. There were several important results: (1) ∆PRI(525,570), ∆PRI(531,570), ∆PRI(535,570), and ∆PRI(545,570) could be used for estimation of most of the photosynthetic parameters under light only or under dark only conditions. (2) The combination of dark and light conditions decreased the efficiency of ∆PRIs for the estimation of the photosynthetic parameters; ∆PRI(535,570) and ∆PRI(545,570) had maximal efficiency under these conditions. (3) ∆PRI(515,570) and ∆PRI(525,570) mainly included the slow-relaxing component of PRI; in contrast, ∆PRI(531,570), ∆PRI(535,570), ∆PRI(545,570), and ∆PRI(555,570) mainly included the fast-relaxing component of PRI. These components were probably caused by different mechanisms.
Highlights
Environmental conditions change over time; in particular, there are fluctuations in light intensity [1,2,3], temperature [4,5], precipitation [6,7], etc., with durations from less than one second to days and weeks
We previously showed that a reference wavelength equal to 570 nm is optimal for photochemical reflectance index (PRI) calculation in this object [26], and that light-induced changes in PRIs (∆PRIs) were more effective for the estimation of nonphotochemical quenching of chlorophyll a (NPQ) in peas than the absolute values of these indices [62,64]
Most of these photosynthetic parameters were not saturated in the investigated range of intensities of actinic light; the values of γ(NA) were similar under the intensities of actinic light equal to 344, 830, and 1599 μmol m−2 s−1
Summary
Environmental conditions change over time; in particular, there are fluctuations in light intensity [1,2,3], temperature [4,5], precipitation [6,7], etc., with durations from less than one second to days and weeks. Plants are very sensitive to these fluctuations in environmental conditions, which can act as stressors, inducing a decrease in photosynthetic activity and plant productivity, as well as other changes in physiological processes [1,3,4,8,9]. And remote detection of stressor-induced changes forms the basis of the timely use of methods of plant protection, i.e., it is important for agriculture and environmental conservation [10]. It is shown that these reflectance indices can be used for the effective remote sensing of plants in short-term [13,35,37,38,39], seasonal [20,40,41,42], and multi-year observations [39,43,44]
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