Abstract
Understanding the relative importance of environment and life history strategies in determining leaf chemical traits remains a key objective of plant ecology. We assessed 20 foliar chemical properties among 12 African savanna woody plant species and their relation to environmental variables (hillslope position, precipitation, geology) and two functional traits (thorn type and seed dispersal mechanism). We found that combinations of six leaf chemical traits (lignin, hemi-cellulose, zinc, boron, magnesium, and manganese) predicted the species with 91% accuracy. Hillslope position, precipitation, and geology accounted for only 12% of the total variance in these six chemical traits. However, thorn type and seed dispersal mechanism accounted for 46% of variance in these chemical traits. The physically defended species had the highest concentrations of hemi-cellulose and boron. Species without physical defense had the highest lignin content if dispersed by vertebrates, but threefold lower lignin content if dispersed by wind. One of the most abundant woody species in southern Africa, Colophospermum mopane, was found to have the highest foliar concentrations of zinc, phosphorus, and δ13C, suggesting that zinc chelation may be used by this species to bind metallic toxins and increase uptake of soil phosphorus. Across all studied species, taxonomy and physical traits accounted for the majority of variability in leaf chemistry.
Highlights
Leaf chemistry is fundamental to tree physiology [1,2,3,4], and has evolved in concert with other plant traits to serve plant functional strategies [5,6,7,8,9,10]
Our results reveal high levels of foliar chemical diversity among coexisting savanna woody plant species, suggestive of divergent life strategies
We found that environmental filters were weakly correlated with these chemicals (R2 = 12%), whereas two non-foliar traits—thorn type and seed dispersal mechanism—accounted for nearly as much variance in these chemicals as did species (R2 = 46% for thorn+dispersal, R2 = 54% for species)
Summary
Leaf chemistry is fundamental to tree physiology [1,2,3,4], and has evolved in concert with other plant traits to serve plant functional strategies [5,6,7,8,9,10]. African savannas impose a unique set of selective pressures on the foliar chemistry of woody plants: drought, frequent fires and megaherbivores such as elephants and giraffe, and tree-grass interactions [11,12,13]. Tree Foliar Chemistry in an African Savanna savanna woody plants found foliar condensed tannins, known to protect plant cells against microbial attack, to inactivate digestive enzymes in insect herbivores, and to slow digestion by mammalian herbivores [11]. Cost-benefit analyses have indicated that leaf nitrogen (N) content is significantly lower and lignin content higher in leaves of savanna trees compared to other biomes, suggesting an investment in longevity and toughness at the expense of N-rich photosynthetic compounds, such as Rubisco and chlorophyll [22]
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