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Controls Over Leaf Litter and Soil Nitrogen Fixation in Two Lowland Tropical Rain Forests
Author(s) -
Reed Sasha C.,
Cleveland Cory C.,
Townsend Alan R.
Publication year - 2007
Publication title -
biotropica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.813
H-Index - 96
eISSN - 1744-7429
pISSN - 0006-3606
DOI - 10.1111/j.1744-7429.2007.00310.x
Subject(s) - dry season , wet season , biology , litter , tropical savanna climate , nutrient , biome , agronomy , tropics , plant litter , nitrogen fixation , fixation (population genetics) , rainforest , ecology , ecosystem , biochemistry , genetics , bacteria , gene
Global comparisons suggest that rates of N fixation in tropical rain forests may be among the highest on earth. However, data supporting this contention are rare, and the factors that regulate N fixation within the biome remain largely unknown. We conducted a full‐factorial (N × P) fertilization experiment in two lowland tropical rain forests in Costa Rica to explore the effects of nutrient availability on rates of free‐living N fixation in leaf litter and soil. P fertilization significantly increased N fixation rates in both leaf litter and soil, and the effect was dependent on sampling date. Fertilization with N did not affect rates of N fixation at any time. In addition, variation in N fixation rates measured in unfertilized plots at four sampling time points suggested seasonal variability in N fixation: leaf litter N fixation ranged from 0.36 kg/ha/yr in the dry season to 5.48 kg/ha/yr in the wet season. Soil N fixation showed similar patterns ranging from a dry season low of 0.26 kg/ha/yr to a wet season high of 2.71 kg/ha/yr. While the observed temporal variability suggests potential climatic control over free‐living N fixation in these forests, data suggest that neither soil nor leaf litter moisture alone regulate N fixation rates. Instead, we hypothesize that a combination of ample C availability, low leaf litter N:P ratios, and high rainfall coincide during the latter portions of the rainy season and drive the highest free‐living N fixation rates of the year.