Abstract
Resorption is the active withdrawal of nutrients before leaf abscission. This mechanism represents an important strategy to maintain efficient nutrient cycling; however, resorption is poorly characterized in old‐growth tropical forests growing in nutrient‐poor soils. We investigated nutrient resorption from leaves in 39 tree species in two tropical forests on the Guiana Shield, French Guiana, to investigate whether resorption efficiencies varied with soil nutrient, seasonality, and species traits. The stocks of P in leaves, litter, and soil were low at both sites, indicating potential P limitation of the forests. Accordingly, mean resorption efficiencies were higher for P (35.9%) and potassium (K; 44.6%) than for nitrogen (N; 10.3%). K resorption was higher in the wet (70.2%) than in the dry (41.7%) season. P resorption increased slightly with decreasing total soil P; and N and P resorptions were positively related to their foliar concentrations. We conclude that nutrient resorption is a key plant nutrition strategy in these old‐growth tropical forests, that trees with high foliar nutrient concentration reabsorb more nutrient, and that nutrients resorption in leaves, except P, are quite decoupled from nutrients in the soil. Seasonality and biochemical limitation played a role in the resorption of nutrients in leaves, but species‐specific requirements obscured general tendencies at stand and ecosystem level.
Highlights
Tropical forests store large amounts of aboveground biomass, even though they grow on old, highly weathered infertile soils (Gersmehl, 1976; Vitousek & Sanford, 1986)
Nitrogen and P resorption efficiencies increased with foliar N and P concentrations across species (R2 = 0.27, p < .0001 and R2 = 0.15, p = .013, respectively), whereas K resorption efficiency was only marginally related to foliar K concentration (R2 = 0.08, p = .08; Figure 3), so our second hypothesis establishing that nutrient resorption will be higher for trees with higher foliar nutrient concentrations was only partially supported
Our study of 39 tropical tree species across two sites demonstrated that the resorption efficiencies of N, P, and K are partially dependent on foliar nutrient concentrations, but largely decoupled from soil nutrient stocks, indicating a key role for plant-internal nutrient cycling for maintaining growth despite infertile tropical soils
Summary
Tropical forests store large amounts of aboveground biomass, even though they grow on old, highly weathered infertile soils (Gersmehl, 1976; Vitousek & Sanford, 1986). The resorption of foliar nutrients is activated by kinetin signals, which promote nutrient mobilization through the phloem from old senescent leaves (the source) to other plant organs such as stems, roots, or new leaves (sinks) (Hill, 1980) This process of internal nutrient recycling plays an important role in plant nutrition and survival, allowing plants to be more independent of external conditions (Aerts, 1996b; Brant & Chen, 2015; van Heerwaarden et al, 2002; Killingbeck, 1996; Reed et al, 2012). Resorption efficiencies will be more similar among more closely related than phylogenetically distant species To address these hypotheses, we explored the stocks and the resorption efficiencies of essential elements (N, P, and K) in aboveground (leaves and leaf-litter) and soil compartments during the wet and dry season in two old-growth tropical forests growing on old, nutrient-poor soils
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