LTER: Carbon and Nutrient Relations Among Oligotrophic Forest Communities in the North Central Amazon Basin

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Nutrient limitations appear to be widespread in the oligotrophic rainforest ecosystems of the Rio Negro portion of the Amazon basin. This research will test several hypotheses regarding carbon-nutrient relations and nutrient-use efficiency for these forests. Four discrete primary forest communities (each on different soil type) will be studied, along with a successional community. Species overlap between these communities is minimal, even though all five communities are located within 1 km from each other at San Carlos de Rio Negro, Venezuela. Individuals from 5 species in each community (25 species total) have been monitored for six years, providing baseline data on leaf production and leaf duration. Now nutrient and carbon relations will be studied with respect to leaf longevity and leaf aging and soil nutrient availability. The main hypotheses are that distinct differences will emerge among communities (and species): 1) in leaf morphology and nutrient content, as a result of variation in habitat resource availability and species successional niche, 2) in CO2 assimilation capacity, as function of leaf nutrient content and photosynthetic nitrogen- and phosphorus-use efficiency, 3) in long-term carbon gain and nutrient-use efficiency, as a result of variation in photosynthetic nutrient-use efficiency, leaf longevity, and leaf nutrient retention and retranslocation over time.