U.S. Department of Energy Office of Biological and Environmental Research

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Tropical Forest Soil Carbon Stocks Predicted by Nutrients and Roots, not Aboveground Plant Biomass
Published: January 02, 2018
Posted: January 31, 2018

Soil base cation availability regulates tropical soil C stocks via a negative relationship with fine root biomass.

The Science
Scientists at UCLA and the Smithsonian conducted an extensive study of predictors of tropical soil C stocks to 1 m depth at 48 sites in Panama, including measurements of soil characteristics, plant biomass, and climate. The study revealed a nearly three-fold change in soil C stocks across five soil orders, with soil characteristics like fine root biomass, clay content, and nutrient base cations the strongest predictors of soil C stocks.

The Impact
Tropical forests are the most carbon (C)-rich ecosystems on Earth, containing 25-40% of global terrestrial C stocks. Quantification of aboveground biomass in tropical forests has improved recently, but soil C dynamics remains one of the largest sources of uncertainty in Earth system models. Including soil base cations in C cycle models, and thus emphasizing mechanistic links among nutrients, root biomass, and soil C stocks, will improve prediction of climate-soil feedbacks in tropical forests.

Summary
Overall, soil characteristics were the best predictors of soil C stocks, with no relationship to aboveground plant biomass or litterfall. The best fit model for our data suggested that available base cations provide an indirect control over tropical soil C stocks via a negative relationship with fine root biomass. Soil clay content and rainfall also emerged as significant predictors of soil C. In addition to the nearly three-fold change in soil C stocks, the sites used here covered five soil orders, over 25 geological formations, a two-fold range in rainfall, a 20-fold range in base cations, and a 100-fold range in available P. Thus, although the data come from a relatively restricted geographic region, the diversity of environmental conditions means that the results are likely to be broadly applicable over much larger geographical ranges.

Contacts (BER PM)
Daniela F Cusack
Assistant Professor, Department of Geography, UCLA
dcusack@geog.ucla.edu

(PI Contact)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Funding
Funding was provided by NSF GSS Grant #BCS-1437591 and DOE Office of Science Early Career Research Program Grant DE-SC0015898 to D. F. Cusack, and NERC Grant NE/J011169/1 to O. T. Lewis.

Publications
Cusack D.F., L. Markesteijn, R. Condit, O.T. Lewis, B.L. Turner. “Soil carbon stocks across tropical forests of Panama regulated by base cation effects on fine roots.” Biogeochemistry (2018). [DOI:10.1007/s10533-017-0416-8]

Related Links
Complete data on location, rainfall, geology, soil, litterfall, aboveground and root biomass in 48 plots in central Panama, excel format

Topic Areas:

  • Research Area: Terrestrial Ecosystem Science
  • Research Area: Carbon Cycle, Nutrient Cycling
  • Cross-Cutting: Early Career

 

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