Photosynthetic ecophysiology of evergreen leaves in the woody angiosperms – a review

Abstract

Abstract:Evergreen plants are an important component of many ecosystems of the world and occur in numerous evolutionary lineages. In this article we review phenotypic traits of evergreen woody angiosperms occurring in habitats that regularly experience frost. Leaf anatomical traits such as sclerenchymatic tissues or prominent cuticles ensure mechanical strength while often enhancing tolerance of water deficit. The low ratio of photosynthetic to nonphotosynthetic tissues as well as modified cell wall structure and nitrogen allocation patterns in evergreen leaves result in lower mass-based photosynthetic rate and photosynthetic nitrogen use efficiency in comparison with deciduous leaves. Their photosynthetic apparatus is adapted for the survival of frost in a down-regulated state with potential for photosynthetic activity in winter during periods of permissive temperatures. Leaf structure interacts with the mechanisms of frost survival. Stem xylem in evergreen plants tends to contain smaller diameter conduits incurring greater resistance to freeze/ thaw induced cavitation than in deciduous plants, although at the cost of reduced hydraulic efficiency. In contrast, no such differences in hydraulic conductivity have been documented at the leaf level. There is evidence for reduced structural plasticity of evergreen leaves in response to variability in irradiance, however photosynthetic downregulation occurs in mature leaves in response to self shading. Some evergreen species exhibit slow leaf development and "delayed greening", while in many species aging is also a very protracted process. Finally, evergreen leaves may participate in carbohydrate and, less obviously, in nitrogen storage for the support of spring shoot and foliage growth, although the importance of this function is under debate. In conclusion, the evergreen leaf habit is correlated with numerous structural and functional traits at the leaf and also at the stem level. These correlations may generate trade-offs that shape the ecological strategies of evergreen plants.Additional key words: internal conductance to CO 2 , leaf anatomy, sclerophylly, winter photosynthesis, winter photoinhibition.

Seasonal dynamics of nitrogen level and gas exchange in different cohorts of Scots pine needles: a conflict between nitrogen mobilization and photosynthesis?

“…Thus, in the oldest needle class, in contrast to younger needles, the variability of photosynthesis throughout the growing season appeared to be related to internal tree N dynamics, in agreement with Hypothesis (3). Such slow, extended senescence, sometimes encompassing several years, is characteristic of some other evergreen species (Reich et al 2009;Wyka and Oleksyn 2014). In some species, the N recycled during senescence originates largely from degradation of Rubisco, possibly also including the photosynthetically active pool of this enzyme (Millard and Grelet 2010).…”

Thermal niche predictors of alpine plant species

“…Like their deciduous congenerics, we found most evergreen shrub species were promoted by positive temperatures during summer. Their evergreen habits and the resulting ability to be physiologically active throughout the seasonal cycle whenever permitted by the environmental conditions, however, allowed them to capitalize on additional time windows of photosynthetic opportunities when the potentially competing deciduous species were leafless (Wyka and Oleksyn 2014). Consequently, our thermal niche predictors outside the summer season gained importance.…”

Hierarchy of plasticity traits in responses of Quercus aliena to light conditions and water availability

“…Thicker upper epidermis and compact palisade parenchyma under drought stress improved leaf water balance, and protected inner tissues from damage of high light (Oguchi et al 2003;Guerfel et al 2009;Wyka and Oleksyn 2014). Formation of xylem at midrib with smaller vessel diameter could enhance the structural strength, and reduce risks of embolism in wood subjected to water deficit (Woodruff et al 2008).…”