The role of microsite sunlight environment on growth, architecture, and resource allocation in dominant Acacia tree seed
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The role of microsite sunlight environment on growth, architecture, and resource allocation in dominant Acacia tree seedlings, in Serengeti, East Africa Deusdedith M. Rugemalila T. Michael Anderson
. Scott T. Cory
. William K. Smith
.
Received: 14 May 2020 / Accepted: 18 August 2020 Ó Springer Nature B.V. 2020
Abstract Seedling establishment is a critical life history stage for savanna tree recruitment due to variability in resource availability. While tree–grass competition for water is recognized as an important driver of tree seedling mortality, the importance of sunlight exposure on tree seedling performance has received little attention in savanna ecosystems despite variable seedling light environments caused by heterogeneity in biomass of the grass canopy. We studied the seasonal sunlight micro-environment for two dominant East African tree species (Acacia = Vachellia) robusta (Burch) and A. tortilis (Forssk) under natural field conditions. In the Serengeti National Park, Tanzania, A. robusta trees occur in tall grasslands of the north (shady) and A. tortilis in the southern short grasslands (less shaded). We also designed a greenhouse experiment to quantify sunlight effects on seedling growth, architecture, and resource allocation traits. In the field, A. robusta
seedlings were associated with lower understorey sunlight during the wet season compared to A. tortilis, with this trend switching during the dry season. In the greenhouse experiments, under low sunlight (25% radiation), A. robusta gained height faster than A. tortilis and self-shading among canopy leaves was evident in A. tortilis but not A. robusta. Biomass allocation to leaves, stems, and roots differed between species under different light environments suggesting phenotypic plasticity in response to variable light availability. Our study suggests that microsite light variability should be incorporated in models of the spatial and temporal variability of savanna tree recruitment. Keywords Coexistence Incident sunlight Light interception Seedling recruitment Savanna
Introduction Communicated by Michael John Lawes.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11258-020-01074-5) contains supplementary material, which is available to authorized users. D. M. Rugemalila (&) S. T. Cory W. K. Smith T. M. Anderson Department of Biology, Wake Forest University, Winston-Salem, NC 27109, USA e-mail: [email protected]
A fundamental goal in plant ecology is to understand how plants co-exist and persist under variable and limited resource availability (Foster and Tilman 2003; Tilman 1997). Because of high mortality, the tree seedling stage may be a critical demographic bottleneck for plants in highly seasonal environments (Brodersen et al. 2019; Holdo et al. 2014). Savannas are highly seasonal, and are fire-dependent ecosystems
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Plant Ecol
characterized by a grass-dominated understorey and a spatially heterogeneous distribution of adult
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