Biomass and Leaf Acclimations to Ultraviolet Solar Radiation in Juvenile Plants of Coffea arabica and C. canephora

Abstract

Despite the negative impacts of increased ultraviolet radiation intensity on plants, these organisms continue to grow and produce under the increased environmental UV levels. We hypothesized that ambient UV intensity can generate acclimations in plant growth, leaf morphology, and photochemical functioning in modern genotypes of Coffea arabica and C. canephora. Coffee plants were cultivated for ca. six months in a mini greenhouse under either near ambient (UVam) or reduced (UVre) ultraviolet regimes. At the plant scale, C. canephora was substantially more impacted by UVam when compared to C. arabica, investing more carbon in all juvenile plant components than under UVre. When subjected to UVam, both species showed anatomic adjustments at the leaf scale, such as increases in stomatal density in C. canephora, at the abaxial and adaxial cuticles in both species, and abaxial epidermal thickening in C. arabica, although without apparent impact on the thickness of palisade and spongy parenchyma. Surprisingly, C. arabica showed more efficient energy dissipation mechanism under UVam than C. canephora. UVam promoted elevated protective carotenoid content and a greater use of energy through photochemistry in both species, as reflected in the photochemical quenching increases. This was associated with an altered chlorophyll a/b ratio (significantly only in C. arabica) that likely promoted a greater capability to light energy capture. Therefore, UV levels promoted different modifications between the two Coffea sp. regarding plant biomass production and leaf morphology, including a few photochemical differences between species, suggesting that modifications at plant and leaf scale acted as an acclimation response to actual UV intensity.

Kaolin Film Increases Gas Exchange Parameters of Coffee Seedlings During Transference From Nursery to Full Sunlight

“…Without KF, C. canephora kept the leaves cooler at midday than C. arabica, which was likely related primarily to the higher E values linked to higher g s , knowing that the increased transpiration rate results in increased latent heat loss and reduced leaf temperature (Ainsworth and Rogers, 2007;Jones, 2018). Additionally, overall, non-KF treated leaves from C. canephora have showed higher stomatal density than C. arabica (Rodrigues et al, 2018;Bernado et al, 2021), helping to understand the species-specific responses, i.e., could allow C. canephora leaves to respond more rapidly to changing environmental cues. C. arabica also showed increased g s and E values when treated with KF, but the difference in g s and E between the two coffee species was reduced with KF spraying, resulting from the reduction in C. canephora efforts to acclimatize on high light and temperature.…”

“…Kaolin applied at high doses acts as an antitranspirant, impacting the direction of leaf A and E reductions in some stages of grapevines (Frioni et al, 2019(Frioni et al, , 2020. Two coffee species differ in anatomical leaf characteristics: C. arabica is characterized by a greater thickness of the abaxial epidermis and the spongy parenchyma, and by the lower thickness of the palisade parenchyma and reduced stomatal density than C. canephora (Bernado et al, 2021).…”

“…In coffee, generally limited and low A is explained by stomatal factor limitations, followed by the mesophyll and biochemical constraints (Martins et al, 2014). Moreover, coffee plants showed significant sensibility to UV radiation, mainly C. canephora, which displayed reduced root and total biomass, number of leaves and leaf area, increased leaf elongation rate under ambient compared with reduced UV radiation (Bernado et al, 2021).…”

“…In the post-planting period, under the combination of elevated air temperatures and elevated solar irradiance, especially its UV bands (Ulm and Jenkins, 2015;Bernado et al, 2021), one physiological disorder called leaf sunburn can occur in coffee seedlings (Santos et al, 2016). Sunburn is expressed by symptoms of chlorosis and necrosis in a great number of species (Racskó et al, 2010).…”

Morphophysiological and Proteomic Responses on Plants of Irradiation with Electromagnetic Waves

“…Generally, some plants such as coffee are naturally adapted to UV and continued to grow and produce under the increased environmental UV levels [68], owing to stocky phenotype and morphological traits of their leaf, such as increased stomatal density, epidermal thickness, and sunscreen accumulation in the leaf surface [69]. For most of the other plants, UV acted both as an environmental stress eliciting a stress-control response [70] and an informational development signal inducing photomorphogenic responses [71].…”