Occurrence of homobaric and heterobaric leaves in two forest types of southern Brazil

Abstract

In ombrophilous forests, light stratifi cation provokes diff erent adjustments by plants for better use of the environmental conditions of each stratum. Among the morphological traits that vary with strata, the presence of bundle sheath extensions (BSEs) is related to water transport, photosynthesis, and leaf mechanical support and classifi es leaves as homobaric or heterobaric. Th is study analyzed the proportion of these types of leaves in a Lowland Ombrophilous Dense Forest (LLODF) and a Mixed Ombrophilous Forest (MOF), and among the strata of each forest type. Th e morphological leaf traits of 89 LLODF tree species and 57 MOF tree species were examined. Th e proportion of homobaric and heterobaric leaves did not diff er between forests. However, in both forest types, the distribution of species with heterobaric or homobaric leaves depended on strata, with heterobaric species occurring mainly in higher strata, and homobaric species in lower strata. Th us, light stratifi cation acts as an ecological fi lter on the composition of the vegetation of these forests, favoring heterobaric species in places with higher light intensity and temperature, such as the highest strata of canopy. On the other hand, homobaric species are more frequent in lower strata, where light is less available and humidity higher.

Leaf toughness increases with tree height and is associated with internal leaf structure and photosynthetic traits in a tropical rain forest

“…Lower midday water potential was observed in leaves with denser BSEs in temperate trees, consistent with our prediction (Kawai et al, 2017). In various forest ecosystems, the proportion of heterobaric species to homobaric species increases with tree height (McClendon, 1992;Boeger et al, 2016;Kenzo et al, 2016). For example, in the studied tropical rainforest, 78% of canopy trees have heterobaric leaves, whereas 93% of understory trees and 67% of sub-canopy trees have homobaric leaves (Appendix 3).…”

“…The presence or absence of BSEs affects not only physiological functions but also the ecological distribution of plants in tropical rainforests. Specifically, there is clear evidence of niche segregation, with a higher proportion of homobaric species found among forest floor shrubs, and a higher proportion of heterobaric species in high-light environments, such as the canopy and canopy gaps (Kenzo et al, 2007;Boeger et al, 2016). In addition, leaf type does not vary ontogenetically within species (Wylie, 1952).…”

The Optical Properties of Leaf Structural Elements and Their Contribution to Photosynthetic Performance and Photoprotection

“…Probably for this reason, heterobaric leaf species (mainly trees) tend to be distributed in high irradiance, occasionally xerothermic environments, such as the Mediterranean forest gaps; a similar distribution characterizes species of the Proteaceae family with sclerophyllous leaves referred above [ 86 ]. In contrast, homobaric leaf species (mainly herbs) are found in shady and moist environments such as the forest understory or their biological cycle is confined within the favourable season [ 91 , 111 , 112 , 113 ]. The heterobaric character is also stronger at an intraspecific level as a result of acclimatization to xerothermic conditions and high light intensities.…”

Distribution of homobaric and heterobaric leafed species in the Brazilian Cerrado and seasonal semideciduous forests

“…The highest thickness of the homobaric leaves as in shrub and trees in Cerrado and seasonal forest is a common trait to other studies (Terashima, 1992;Kenzo et al, 2007;Liakoura et al, 2009;Pieruschka et al, 2010;Lynch et al, 2012;Boeger et al, 2016) and has been associated to a well-developed spongy parenchyma (Boeger et al, 2016). According to Vogelman et al (1996), a thicker spongy parenchyma is advantageous for capturing diffuse light, mainly under limited light conditions.…”

“…This adaptation has been considered important in terms of specific growth environments and/or life-form types (Kenzo et al, 2007;Rossato et al, 2015). In addition, studies indicate that homobaric leaves are thicker than heterobaric leaves (Boeger et al, 2016) and present a higher proportion of photosynthetic areas in the mesophyll which is advantageous for capturing diffuse light (Terashima, 1992).…”