Morpho‐anatomical and physiological differences between sun and shade leaves in Abies alba Mill. (Pinaceae, Coniferales): a combined approach

Abstract

Morphology, anatomy and physiology of sun and shade leaves of Abies alba were investigated and major differences were identified, such as sun leaves being larger, containing a hypodermis and palisade parenchyma as well as possessing more stomata, while shade leaves exhibit a distinct leaf dimorphism. The large size of sun leaves and their arrangement crowded on the upper side of a plagiotropic shoot leads to self-shading which is explainable as protection from high solar radiation and to reduce the transpiration via the lamina. Sun leaves furthermore contain a higher xanthophyll cycle pigment amount and Non-Photochemical Quenching (NPQ) capacity, a lower amount of chlorophyll b and a total lower chlorophyll amount per leaf, as well as an increased electron transport rate and an increased photosynthesis light saturation intensity. However, sun leaves switch on their NPQ capacity at rather low light intensities, as exemplified by several parameters newly measured for conifers. Our holistic approach extends previous findings about sun and shade leaves in conifers and demonstrates that both leaf types of A. alba show structural and physiological remarkable similarities to their respective counterparts in angiosperms, but also possess unique characteristics allowing them to cope efficiently with their environmental constraints.

Dynamic acclimation to sunlight in an alpine plant, Soldanella alpina L.

“…The increase in leaf thickness, observed in Hedera Remarkably, the stomatal density increased in shade-sun transferred leaves compared to shade leaves. A higher stomatal density in sun compared to shade grown leaves was widely reported (Casson and Gray 2007, Gerardin et al 2018, Dörken and Lepetit 2018, Quevedo-Rojas et al 2018 and is usually accompanied by higher stomatal conductance. This was not the case in shade-sun transferred S. alpina leaves, where stomatal conductance to water vapour remained lowest.…”

The foliar characters in Callitris (Callitroideae, Cupressaceae s. str.) and their evolutionary and ecological significance

“…). Suggested functions of such tissue include protecting the mesophyll from excess solar radiation, reducing water loss via the lamina and preventing leaf collapse during low water potential in drought (Dörken & Lepetit ). Jordan et al.…”

“…The presence of a hypodermis predominantly in the most light‐exposed part of the leaves accords with work on Abies alba Mill. (Pinaceae) showing a distinct hypodermis on sun leaves but a virtual absence on shade leaves (Dörken & Lepetit ).…”

The flattened and needlelike leaves of the pine family (Pinaceae) share a conserved genetic network for adaxial-abaxial polarity but have diverged for photosynthetic adaptation

“…Generally, needlelike leaves appear to be more drought-resistant than flattened leaves [ 5 , 6 ]. Previous studies on conifer “needles” have evaluated their morphology and physiology [ 7 – 9 ] but rarely focused on their developmental mechanisms and evolution. Pinaceae (the pine family), comprising 11 genera and approximately 230 species, is the most important component of the coniferous forests in the Northern Hemisphere, with both needlelike and flattened leaves [ 4 , 10 , 11 ].…”