GROWTH AND PHOTOSYNTHETIC USE EFFICIENCY OF NITROGEN AND PHOSPHORUS IN SAPLINGS OF AMAZONIAN TREE SPECIES

In the Amazon Rainforest, photosynthesis and tree growth may be limited by the availability of nutrient. Thus, the objectives of this study were to determine the effect of leaf N and P content on photosynthesis, and to assess plant growth in response to understory light in ten tree species in Central Amazonia. Data were collected in January 2008. The photosynthetic capacity (A(pot)) of leaves positively increased with foliar N and P content, but it was only responsive to P use efficiency. The contents of N and P increased as understory irradiance increased. In addition, we found a positive relationship between N content and the N/P ratio. On the contrary, the relationship between P content and the N/P ratio was negative. Specific leaf area was negatively correlated with N and P. N use efficiency declined with increases with the N/P ratio, but the N/P ratio had no significant effect on P use efficiency. Growth in diameter increased with understory light. In conclusion, saplings were highly sensitive to variations in light intensity, and P was used with high efficiency in studied species.