Relationships between crown architecture and available irradiance in two cerrado species with different leaf phenologies

Abstract

-(Relationships between crown architecture and available irradiance in two cerrado species with different leaf phenologies). Structural differences between cerrado species with different leaf phenologies are linked to crown architecture, leaf production, and biomass allocation to shoots and leaves. The present study characterized crown structures and the patterns of biomass allocation to leaves and shoots in two woody cerrado species with contrasting leaf phenologies and quantifi ed the irradiance reaching their leaves to determine the best period during the day for photosynthetic activity. The shoots and leaves of fi ve individuals of both Annona coriacea (deciduous) and Hymenaea stigonocarpa (evergreen) were collected along a 50 m transect in a cerrado fragment within the urban perimeter of Catalão -GO, to determine their patterns of biomass allocation in their crowns. The evergreen H. stigonocarpa had signifi cantly higher mean values of shoot inclination (SI), petiole length (PL), leaf area (LA), leaf display index (LDI), and individual leaf area per shoot (ILA), while the deciduous species A. coriacea had signifi cantly higher leaf numbers (LN). The more complex crown of H. stigonocarpa had shoots in more erect positions (orthotropic), with intense self-shading within shoots; A. coriacea, on the other hand, had slanting (plagiotropic) shoots in the crown, allowing similar irradiance levels to all leaf surfaces. The production of plagiotropic shoots by the deciduous species (A. coriacea) is a strategy that enables its use of incident sunlight early in the morning and preventing excessive water loss or excessive irradiance. Hymenaea stigonocarpa (an evergreen), by contrast, had orthotropic shoots and uses intense self-shading as a strategy to avoid excessive irradiance, especially at midday. Differences in crown architectures between evergreen and deciduous species of cerrado sensu stricto can therefore be viewed as adaptations to the environmental light regime.

Evidence of the effects of fire on branching and leaf development in cerrado trees

“…Only four studies deal with whole crown architecture (Souza et al 2011;Santos et al 2012) or modular growth (Damascos et al 2005;Damascos 2008) of woody cerrado species. In general, cerrado species with perennial foliage adjust shoot growth to the rainy period, while those with deciduous foliage produces leaves and shoots before the fi rst rains (Damascos et al 2005;Lenza & Klink 2006;Damascos 2008).…”

“…On the other hand, evergreens have orthotropic shoots, where distal shoot leaves receive greater irradiance than basal shoot leaves. These differences result in a complex crown in evergreens that has more shoots and nodes than in deciduous trees (Souza et al 2011), which affects light utilization during the day (Santos et al 2012). However, the crown architecture in cerrado habitats can be modified by environmental characteristics such as periodic fires.…”