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Biogeochemical Relationships of a Subtropical Dry Forest on KarstAuthor(s): E. Medina; E. Cuevas; H. Marcano-Vega; E. Meléndez-Ackerman; E.H. Helmer
Source: Caribbean Naturalist. No. 41:1-24.
Publication Series: Scientific Journal (JRNL)
Station: International Institute of Tropical Forestry
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DescriptionTropical dry forests on calcareous substrate constitute the main vegetation cover in many islands of the Caribbean. Dry climate and nutrient scarcity in those environments are ideal to investigate the potential role of high levels of soil calcium (Ca) in regulating plant selection and productivity. We analyzed the elemental composition of soil, loose litter, and leaf samples of the woody vegetation on the plateau of Mona Island, an emergent block of carbonate rock in the Caribbean located between Puerto Rico and the Dominican Republic, to explore the nutrient relationships of plants growing on calcareous substrates. The mineral soil has an elemental composition characterized by high levels of aluminum (Al) and iron (Fe) in agreement with the hypothesis that it derives in part from sediments transported by rivers eroding plutonic rocks, and deposited before the massive lifting of biological limestone. Calcium concentration varied within sites, and Ca–Al and Ca–Fe correlations were negative in soils and positive in plant material, implying that element uptake from these soils depends on acidification of the rhizosphere. This acidification should be high enough to extract carbonate-bound elements and solubilize Al, Fe, and probably phosphate (P) compounds. The most abundant cation in leaves was Ca, followed by potassium (K) and magnesium (Mg); Ca/K and Ca/Mg molar ratios averaged 2 and 3, respectively, indicating that most species maintain K and Mg uptake in the presence of high Ca levels. Both N and P concentrations and N/P ratios in soils, loose litter, and woody plant leaves indicate comparatively high P availability. Based on elemental composition, 3 species groups were identified: one associated with higher values of N, P, and K; a second characterized by the lowest concentrations of Mg, Ca, and Al; and a third containing species with greater relative amounts of Ca, Mg, and Al, and higher Ca:K ratios. Differences are probably the result of species-specific requirements, but ecological implications are not clear yet. Phylogenetic arrangement of species showed that Ca concentration varies smoothly between botanical orders, revealing a phylogenetic signature. Brassicales, Ericales, and Lamiales had the highest Ca values, whereas Fabales and Arecales were at the lower end of the concentration scale. Aluminum showed a tight correlation with Ca within the plant orders.
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CitationMedina, E.; Cuevas, E.; Marcano-Vega, H.; Meléndez-Ackerman, E.; Helmer, E.H. 2017. Biogeochemical Relationships of a Subtropical Dry Forest on Karst. Caribbean Naturalist. No. 41:1-24.
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