Abstract
Summary Plant biomass allocation may be optimized to acquire and conserve resources. How trade‐offs in the allocation of tropical tree seedlings depend on different stressors remains poorly understood. Here we test whether above‐ and below‐ground traits of tropical tree seedlings could explain observed occurrence along gradients of resources (light, water) and defoliation (fire, herbivory).We grew 24 tree species occurring in five African vegetation types, varying from dry savanna to moist forest, in a glasshouse for 6 months, and measured traits associated with biomass allocation.Classification based on above‐ground traits resulted in clusters representing savanna and forest species, with low and high shoot investment, respectively. Classification based on root traits resulted in four clusters representing dry savanna, humid savanna, dry forest and moist forest, characterized by a deep mean rooting depth, root starch investment, high specific root length in deeper soil layers, and high specific root length in the top soil layer, respectively.In conclusion, tree seedlings in this study show root trait syndromes, which vary along gradients of resources and defoliation: seedlings from dry areas invest in deep roots, seedlings from shaded environments optimize shoot investment, and seedlings experiencing frequent defoliation store resources in the roots.
Highlights
Plant species’ performance is greatly dependent on resource management – the balance between acquisition and conservation
The dry savanna cluster was characterized by a greater MRD (28.8 Æ 2.06 cm), a large Root mass fraction (RMF) (0.40 Æ 0.04), an intermediate specific root length at shallow depth (SRL fraction 1 = 0.24 Æ 0.05), a significantly lower specific root length at deeper depth than the equal distribution null hypothesis of 0.25 (SRL fraction 3 = 0.16 Æ 0.02) and a high starch content (12.2 Æ 2.1%; Fig. 4; Tables S3, S4)
The humid savanna cluster was characterized by a smaller MRD (15.9 Æ 1.37 cm), a large RMF (0.52 Æ 0.05), a lower SRL fraction 1 than the equal distribution null hypothesis (0.12 Æ 0.02), a higher SRL fraction 3 than the equal distribution null hypothesis (0.35 Æ 0.02) and a high starch content (16.6 Æ 2.6%) (Fig. 4; Tables S3, S4)
Summary
Plant species’ performance is greatly dependent on resource management – the balance between acquisition and conservation. In drier areas, where water is the limiting resource as evaporative demand exceeds the amount of precipitation, plants require increased below-ground biomass allocation to form long roots that reach deeper available soil water in order to satisfy water demand (Canadell et al, 1996; Nicotra et al, 2002; Schenk & Jackson, 2002; Laio et al, 2006; Markesteijn & Poorter, 2009; Poorter et al, 2012). This investment should come at the cost of shoot biomass
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