Biological Nitrogen Fixation in Two Tropical Forests: Ecosystem-Level Patterns and Effects of Nitrogen Fertilization

By D. Cusack, Whendee Silver, William H. McDowell. Ecosystems, 2009

166 citations recorded by the source corpus.

Humid tropical forests are often characterized by large nitrogen (N) pools, and are known to have large potential N losses. Although rarely measured, tropical forests likely maintain considerable biological N fixation (BNF) to balance N losses. We estimated inputs of N via BNF by free-living microbes for two tropical forests in Puerto Rico, and assessed the response to increased N availability using an on-going N fertilization experiment. Nitrogenase activity was measured across forest strata, including the soil, forest floor, mosses, canopy epiphylls, and lichens using acetylene (C2H2) reduction assays. BNF varied significantly among ecosystem compartments in both forests. Mosses had the highest rates of nitrogenase activity per gram of sample, with 11 ± 6 nmol C2H2 reduced/g dry weight/h (mean ± SE) in a lower elevation forest, and 6 ± 1 nmol C2H2/g/h in an upper elevation forest. We calculated potential N fluxes via BNF to each forest compartment using surveys of standing stocks. Soils and mosses provided the largest potential inputs of N via BNF to these ecosystems. Summing all components, total background BNF inputs were 120 ± 29 μg N/m2/h in the lower elevation forest, and 95 ± 15 μg N/m2/h in the upper elevation forest, with added N significantly suppressing BNF in soils and forest floor. Moisture content was significantly positively correlated with BNF rates for soils and the forest floor. We conclude that BNF is an active biological process across forest strata for these tropical forests, and is likely to be sensitive to increases in N deposition in tropical regions.

Subfields: Ecology, Environmental Chemistry, Soil Science

View Paper: https://www.semanticscholar.org/paper/deec6f1799da1f48a505fb67333d5e419abf4b89

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Ecology

1. C. Cleveland
2. A. Townsend
3. S. Reed
4. D. Cusack

In Environmental Chemistry

1. C. Cleveland
2. S. Reed
3. A. Townsend
4. M. Spohn

In Soil Science

1. C. Cleveland
2. A. Townsend
3. S. Reed
4. D. Cusack

Citations in the corpus

• Global change effects on humid tropical forests: Evidence for biogeochemical and biodiversity shifts at an ecosystem scale (2016, background): “A similar trend of increased foliar P at drier sites was observed across a rainfall gradient of 1800–3500mmmean annual precipitation (MAP) in Panama [Santiago et al., 2005].”
• Relationships among phosphorus, molybdenum and free-living nitrogen fixation in tropical rain forests: results from observational and experimental analyses (2013, background): “A number of biotic and abiotic factors—including temperature, species composition and nutrient availability—affect N fixation rates (Sprent and Sprent 1990; Vitousek and Howarth 1991; Vitousek and Field 1999; Vitousek et al. 2002; Hicks et al. 2003; Cusack et al. 2009).”