02404naa a2200301 a 450000100080000000500110000800800410001910000180006024501240007826000090020252014980021165000130170965000270172265000170174965000220176665000190178865000240180765000250183165000220185665000130187865300300189165300280192165300250194970000250197470000260199970000200202577300570204519151122012-08-07       2011    bl uuuu     u00u1 u    #d1 aMARKEWITZ, D.  aSoil and tree response to P fertilization in a secondary tropical forest supported by an Oxisol.h[electronic resource]  c2011  aAbstract: Abstract Mature tropical forests are considered to be P limited and to cycle P efficiently. Whether P limitations are significant in younger secondary tropical forests, how- ever, remains largely unexplored. This study evaluated P limitation by observing the P fertilizer response of a natu- rally regenerated 24-year-old forest and its soil. In February 1999, six 20×20-m plots were established in secondary forest in the Brazilian Amazon. After 1 year of pre- treatment tree measurements, 50 kg Pha-1 was applied in January 2000 and again in January 2001. Soil sorption of P was relatively low (~100 micrograms g-1) in the surface 0–20 cm while sorption increased to ~180 micrograms g-1 at 20–50 cm and approached ~500 micrograms g-1 for the 50- to 200-cm layers. Soil P in 0–10 cm, measured as sequentially extractable fractions (resin, HCO3-Pi, NaOH-Pi, NaOH-Po, and 1 M HCl), in- creased shortly after fertilization and could account for nearly all the 50 kg Pha-1 added at each date. During the   following 6 years, soil P in fertilized plots declined in all pools other than resin P, and by June 2006, concentrations returned to pre-fertilization levels. Despite the increase in extractable P with fertilization, increased tree growth was not detected from stand age 25 to 31 years. It appears that during secondary forest succession at this site, the forest P cycle was conservative so as to maintain available P at a sufficient concentration to meet forest P demands.  aAmazonia  aPhosphorus fertilizers  aRain forests  aSecondary forests  aSoil fertility  aFertilidade do solo  aFloresta secundária  aFloresta tropical  aFósforo  aFracionamento de fósforo  aLimitação de fósforo  aSorção de fósforo1 aFIGUEIREDO, R. de O.1 aCARVALHO, C. J. R. de1 aDAVIDSON, E. A.  tBiology and Fertility of Soils, Berlingv. 48, 2011.