Expanding our understanding of leaf functional syndromes in savanna systems: the role of plant growth form

Abstract

The assessment of leaf strategies has been a common theme in ecology, especially where multiple sources of environmental constraints (fire, seasonal drought, nutrient-poor soils) impose a strong selection pressure towards leaf functional diversity, leading to inevitable tradeoffs among leaf traits, and ultimately to niche segregation among coexisting species. As diversification on leaf functional strategies is dependent on integration at whole plant level, we hypothesized that regardless of phylogenetic relatedness, leaf trait functional syndromes in a multivariate space would be associated with the type of growth form. We measured traits related to leaf gas exchange, structure and nutrient status in 57 coexisting species encompassing all Angiosperms major clades, in a wide array of plant morphologies (trees, shrubs, sub-shrubs, herbs, grasses and palms) in a savanna of Central Brazil. Growth forms differed in mean values for the studied functional leaf traits. We extracted 4 groups of functional typologies: grasses (elevated leaf dark respiration, light-saturated photosynthesis on a leaf mass and area basis, lower values of leaf Ca and Mg), herbs (high values of SLA, leaf N and leaf Fe), palms (high values of stomatal conductance, leaf transpiration and leaf K) and woody eudicots (sub-shrubs, shrubs and trees; low SLA and high leaf Ca and Mg). Despite the large range of variation among species for each individual trait and the independent evolutionary trajectory of individual species, growth forms were strongly associated with particular leaf trait combinations, suggesting clear evolutionary constraints on leaf function for morphologically similar species in savanna ecosystems.

Leaf anatomical traits of non-arboreal savanna species along a gradient of tree encroachment

“…irradiance conditions (Rossatto & Franco 2017). Despite the fact that this pattern was clearly observed in the set of typical savanna species studied here, their values of SLA were higher and their tissue thicknesses were lower than those reported for typical non-arboreal savanna species in Central Brazil (see the study by Rossatto et al 2015).…”

“…Considering these results in the context of forest expansion over savannas (Stevens et al 2017) and the ecophysiology of non-arboreal savanna plants (Rossatto & Franco 2017), it can be postulated that the persistence of non-arboreal plants in encroached situations may occur only with the set of leaf anatomical strategies presented here by the FS plants. As the TS species showed thicker leaves, with anatomical traits that are advantageous to survive under elevated light irradiances (Rossatto et al 2015;Rossatto & Franco 2017), this may imply that they cannot thrive under shaded conditions, which in turn can explain why the diversity of such species drastically decrease from the TS to the FS (Pinheiro et al 2016).…”

“…As the TS species showed thicker leaves, with anatomical traits that are advantageous to survive under elevated light irradiances (Rossatto et al 2015;Rossatto & Franco 2017), this may imply that they cannot thrive under shaded conditions, which in turn can explain why the diversity of such species drastically decrease from the TS to the FS (Pinheiro et al 2016). The disappearance of such typical savanna species may occur because their set of anatomical leaf traits are not specialized in capturing low and diffuse light; this can drastically affect the carbon balance, probably leading plants to carbon starvation (Sevanto et al 2014).…”

Leaf traits combinations may explain the occurrence of savanna herbaceous species along a gradient of tree encroachment

“…This is particularly the case for traits associated with carbon gain, considering morphological (specific leaf area) and physiological aspects (maximum photosynthesis and stomatal conductance) (Pérez-Harguindeguy et al 2013). Many studies reported how these traits enable plant persistence in savanna environments (Lemos Filho 2000;Prado et al 2004;Franco et al 2005;Habermann et al 2011;Souza et al 2015;Rossatto and Franco 2017); which are characterized by a series of selective pressures such as fire, rainfall seasonality, lower content of soil nutrients and elevated irradiance (Franco 2002). Such studies, however, focused only on tree species, a diverse, but not unique, component of the savanna ecosystem.…”

The Leaf as a Sustainable and Renewable System

“…The 'leaf' is one of the three organs of vascular seed plants, taxonomically classified under angiosperms. The remaining two, namely root and stem of a vascular plant, facilitate sprouting, support the function of a leaf to assimilate solar energy through photosynthesis and generate biochemical energy through respiration (Tanaka et al, 2015;de la Riva et al, 2016;Rossatto and Franco, 2017). Hence, leaves, although looking flexible, feeble, thin and vulnerable, provide innumerable cubic metre surface area in the canopy for the absorption of blue and red wavelengths from sunlight and therefore contribute to the enhancement of biomass (Tanaka et al, 2015).…”