Chlorophylls (Chl) are important pigments in plants that are used to absorb photons and release electrons. There are several types of Chls but terrestrial plants only possess two of these: Chls a and b. The two pigments form light-harvesting Chl a/b-binding protein complexes (LHC), which absorb most of the light. The peak wavelengths of the absorption spectra of Chls a and b differ by c. 20 nm, and the ratio between them (the a/b ratio) is an important determinant of the light absorption efficiency of photosynthesis (i.e., the antenna size). Here, we investigated why Chl b is used in LHCs rather than other light-absorbing pigments that can be used for photosynthesis by considering the solar radiation spectrum under field conditions. We found that direct and diffuse solar radiation (PAR_dir and PAR_diff, respectively) have different spectral distributions, showing maximum spectral photon flux densities (SPFD) at c. 680 and 460 nm, respectively, during the daytime. The spectral absorbance spectra of Chls a and b functioned complementary to each other, and the absorbance peaks of Chl b were nested within those of Chl a. The absorption peak in the short wavelength region of Chl b in the proteinaceous environment occurred at c. 460 nm, making it suitable for absorbing the PAR_diff, but not suitable for avoiding the high spectral irradiance (SIR) waveband of PAR_dir. In contrast, Chl a effectively avoided the high SPFD and/or high SIR waveband. The absorption spectra of photosynthetic complexes were negatively correlated with SPFD spectra, but LHCs with low a/b ratios were more positively correlated with SIR spectra. These findings indicate that the spectra of the photosynthetic pigments and constructed photosystems and antenna proteins significantly align with the terrestrial solar spectra to allow the safe and efficient use of solar radiation.

Satellite remote sensing (RS) is useful to indirectly evaluate the spatial and temporal variability of land uses, land-cover changes, aboveground biomass of vegetation, leaf-area index of terrestrial vegetation canopies, and plant phenology. These observations allow us to gain a deeper understanding of the spatial and temporal variability of ecosystem structure, ecosystem functions, and biodiversity under climate change. However, satellite RS observations include uncertainties and other issues, and our ecological understanding of satellite RS-observed data is still insufficient. To solve these issues and to better understand the ecological meaning, we need to collect abundant ground-truth data from multiple field sites to validate satellite RS-observed data and conduct integrated analyses using both types. To enhance the development of phenology observation and land-use and land-cover change studies, the Phenological Eyes Network (PEN) and the Site-based dataset for Assessment of Changing Land cover by JAXA project (SACLAJ) were established. In this chapter, we first introduce some of our findings from these two projects, and then we discuss the usability, other related issues, and the outlook of integrated ecosystem studies that use both in situ and satellite RS-observed data.