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

Wallace De Paula Bernado,Ana Cabrera Abraham,Weverton Pereira Rodrigues,Dhiego Da Silva Oliveira,Maura Da Cunha,Eliemar Campostrini,Miroslava Rakocevic,Anne Reis Santos,Danilo Força Baroni,Saulo Pireda,Katherine Fraga Ruas,José Cochicho Ramalho

doi:10.3390/plants10040640

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.

Highlights

Climate changes have important potential impacts on the structure, function, and diversity of terrestrial ecosystems and national economies
On 2 June 2018, 120-day-old C. arabica and C. canephora seedlings produced from seeds and cuttings, respectively, were transplanted to 32-L pots, which was considered as the beginning of the experiment and denominated as the first day after transplanting (DAT)
In the evolution of two economically important coffee species, from forest shade in their African centers of origin, to the monoculture cultivated under the full sunlight, various acclimations have developed to mitigate the possible damage caused by increased levels of UV solar radiation

Summary

Introduction

Climate changes have important potential impacts on the structure, function, and diversity of terrestrial ecosystems and national economies. Estimates of stratospheric ozone depletion and associated changes in ultraviolet radiation levels (200–400 nm) suggest that solar radiation can be one of the most damaging stress factors for many crops [1,2]. Current estimates of the ultraviolet index (UVI), thirty years after the considerations proposed by the Montreal Protocol, show that the prohibition of substances that deplete the ozone layer is highly efficient for the recovery of stratospheric ozone [1]. C. arabica is originally from the African tropical rainforests of Ethiopia, Kenya, and Sudan, and is found at high altitudes of 1600–2800 m, with an average annual temperature between 18 and 22 ◦C, and annual precipitation ranging from 1600 to 2000 mm [4]. Despite the well-described environment under which coffee species have evolved, information about the impacts of UV radiation on these two economically important species is lacking

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