Nitrogen fixation and phosphatase activity of 97 nitrogen-fixing and non-fixing trees in Panama

The dataset includes the original values for all variables except nitrogen fixation and phosphatase activity, which represent the mean across replicates within a tree (three replicates for fixation rate, five replicates for phosphatase activity). Data have not been transformed and no outliers were removed.

Nitrogen fixation was measured using three approaches: (1) To measure nodule biomass, six 5.5 cm diameter soil cores were taken from within two meters of the base of the tree and examined for root nodules in the lab. (2) To measure rates of fixation within the nodules of the majority of trees, nodules were excavated from fine roots at the base of each tree and acetylene reduction assay was conducted immediately. (3) To obtain the conversion of acetylene reduced to nitrogen fixed, nodules were excavated from fine roots at the base of a subset of trees and were incubated with labeled 15N and later analysed with isotope ratio mass spectrometry to determine the nitrogen fixed relative to non-enriched control nodules for each tree. Data were expressed as nodule biomass, nitrogen fixation rate converted to grams nitrogen fixed per area of rooting zone of the focal tree.