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There is considerable interest in the potential use of soils to sequester carbon for climate change mitigation. As such, there is a need to evaluate the potential for carbon accumulation in tropical regions. We compared the effects of three annual additions of nitrogen and/or phosphorus on soil carbon and nitrogen contents and pools (bulk soil, macro-, meso-, and microaggregates) of two regenerating secondary tropical dry forest differing in nutrient status and succession stage (10-year-old early-succession stage and approximately 60-year-old late-succession stage). The selected forest sites were located on a shallow calcareous soil in the Yucatá n Peninsula (Mexico). The primary production is limited by nitrogen and phosphorus in earlysuccession stage and by phosphorus in late-succession stage. In each forest site, four independent plots (12 3 12 m 2 ) were established, the treatments being: controls and plots fertilized during three consecutive years with nitrogen, phosphorus, or nitrogen plus phosphorus. In both forests, soil carbon and nitrogen contents were consistently high, with soil carbon:nitrogen ratios generally greater than 10. Results indicate that usually there are no significant increases of soil carbon stock associated to late succession but can be increased to 3.7 MgÁha 21 Áyr 21 with adoption of fertilizer practices. The potential soil carbon sequestration in early-succession forest was estimated to be 2.7 MgÁha 21 Áyr 21 , and there is no indication that fertilization improves carbon sequestration. In short, results suggest that the soil potential for carbon sequestration in these ecosystems is high and depends on the specific nutrient status of the site.

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