Abstract
The objective of this work was to study physiological characteristics and photosynthetic apparatus in differentially pigmented leaves of three Chinese kale cultivars. Chlorophyll (Chl) fluorescence and photochemical reflectance index (PRI) measurements in green, yellow-green, and dark-green cultivars in response to varying light intensities. As light intensity increased from 200 to 2000 photosynthetic photon flux density (PPFD), fraction of light absorbed in photosystem (PS) II and PRI values in all plants were strongly lowered, but fraction of light absorbed in PSII dissipated via thermal energy dissipation and non-photochemical quenching (NPQ) values in all plants wereremarkably elevated.When plants were exposed to 200 PPFD, the values of fraction of light absorbed in PSII, utilized in photosynthetic electron transport(p), andfraction of light absorbed excitation energy in PSII dissipated via thermal energy dissipation (D), remained stable regardless of the changes in levels of Chla + b. Under 800 and 1200 PPFD, the values of p and electron transport rate (ETR) decreased, but D and NPQ increased as Chla + bcontent decreased, suggesting that decrease inChla + bcontent led to lower PSII efficiency and it became necessary to increase dissipate excess energy. On the contrary, in 2000 PPFD, leaves with lower Chla + bcontent had relatively higher p and electron transport rate (ETR) values and lower D level, as well as tended to increase more in NPQ but decrease more in PRI values. The consistent relations between PRI and NPQ suggest that NPQ is mainly consisted ofthe xanthophyll cycle-dependentenergy quenching.Yellow-green cultivar showed lower Chla + bcontent but high carotenoids/Chla + b ratio and had high light protection ability under high PPFD. The precise management of photosynthetic parameters in response to light intensity can maximize the growth and development of Chinese kale plants.
Highlights
Photosynthesis is biochemically regulated to maintain the balance between the rates of its component processes and concentrations of metabolites in response to environmental changes.Eco-physiological studies require knowledge of the photosynthetic rates of plants under different environmental conditions and a broad range in light intensity
Both chlorophyll fluorescence (ChlF) and reflectance spectroscopy are noninvasive techniques andoften used in physiologicalstudies to investigate a plant0 s response to various abiotic and biotic stresses in controlled environments and in the field [3]
When plants were measuredat 2000 μmol m−2 s−1 photosynthetic photon flux density (PPFD), yellow-green leaves had higher p and electron transportrate (ETR) values. These results indicate that dark-green cultivarfavored moderate PPFDs while yellow-green cultivar was adapted under high light intensities
Summary
Photosynthesis is biochemically regulated to maintain the balance between the rates of its component processes and concentrations of metabolites in response to environmental changes.Eco-physiological studies require knowledge of the photosynthetic rates of plants under different environmental conditions and a broad range in light intensity. The study of photosynthesis irradiance relationships is a basic aspect of plant physiological research and is important for managing various species; photosynthetic light responses can be used to assess the ability to capture light and understand the optimal habitat light intensity conditions of plants [2]. Both chlorophyll fluorescence (ChlF) and reflectance spectroscopy (i.e., photochemical reflectance index, PRI) are noninvasive techniques andoften used in physiologicalstudies to investigate a plant0 s response to various abiotic and biotic stresses in controlled environments and in the field [3]
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