Nondestructive assessment of leaf chemistry and physiology through spectral reflectance measurements may be misleading when changes in trichome density co‐occur

Abstract

Summary• Reflectance indices are frequently used for the nondestructive assessment of leaf chemistry, especially pigment content, in environmental or developmental studies. Since reflectance spectra are influenced by trichome density, and trichome density displays a considerable phenotypic plasticity, we asked whether this structural parameter could be a source of variation in the values of the most commonly used indices.• Trichome density was manipulated in detached leaves of three species having either peltate ( Olea europaea and Elaeagnus angustifolius ) or tubular ( Populus alba ) trichomes by successive removal of hairs. After each dehairing step, trichome density was determined by light or scanning electron microscopy and reflectance spectra were obtained with a diode-array spectrometer.• Although species-specific differences were evident, most of the indices were considerably affected even at low trichome densities. In general, the less-affected indices were those using wavebands within the visible spectral region. The index that could be safely used even at very high hair densities in all species was the red edge index ( λ RE ) for chlorophyll.• The results indicate that changes in reflectance indices should be interpreted cautiously when concurrent changes in trichome density are suspected. In this case, the red edge for chlorophyll content may be the index of choice.

Diurnal patterns of photosynthesis, chlorophyll fluorescence, and PRI to evaluate water stress in the invasive species, Elaeagnus umbellata Thunb.

“…PRI was not effective at tracking changes in DF/F 0 m during water stress in both field and laboratory studies. Future studies are needed to determine if trichome density changes throughout the summer, and if this has an effect on PRI as suggested by Levizou et al (2005). However, our results provide further evidence that Elaeagnus species use other energy dissipative mechanisms for protection of the photosystem.…”

Nondestructive determination of leaf chlorophyll content in two flowering cherries using reflectance and absorptance spectra

“…However, in order to extract pigment information, a range of other factors that also influence vegetation reflectance spectra must be taken into account (Blackburn 2007). Leaf reflectance can vary independently of pigment concentration due to differences in parameters such as leaf thickness and surface characteristics (e.g., hairs and waxes) (Sims and Gamon 2002;Levizou et al 2005). Thus, the relationships between the spectrum and the chlorophyll content must be determined for each species of interest if more accurate quantification is required.…”

Do Reflectance Spectra of Different Plant Stands in Wetland Indicate Species Properties?

“…Different indices that are based on species and/or stand reflectance spectra have been developed to determine the properties of different plant species and plant functional groups (Levizou et al 2005). However, without detailed knowledge of the basic parameters that define the spectral signatures at the species level, reflectance spectra might not provide reliable information (Milton et al 2009).…”

“…It also provides information on leaf biochemistry (Levizou et al 2005;Castro and Sanchez-Azofeifa 2008) and nutrient and water status (Baltzer and Thomas 2005;Asner and Martin 2008) and can serve as a tool for stress detection (Gitelson et al 2002); in some cases, this also allows species classification (i.e. through their spectral signatures) (Castro-Esau et al 2006).…”