The Science

In tropical forests, available phosphorus can limit plant growth. Enzymes released by plant roots and soil microbes can increase phosphorus availability throughout the soil profile. Phosphatase enzymes convert phosphorus bound in organic molecules to an inorganic form that is available to plants. Roots of different tree species can have different effects on phosphatase activity. The number of roots and their activities vary with depth in soil. Current models distribute roots through the soil column; new data on how root traits, soil characteristics, and phosphorus availability vary with soil depth will improve how models represent tree growth in tropical forests.

The Impact

This study pairs new data on soil and root phosphatase with fine-root and soil factors. The root and soil factors regulate enzyme activity in the soil profile. The results improve understanding of root-soil interactions that influence phosphorus dynamics. These findings from a tropical forest in Puerto Rico generated predictive relationships that were robust across a wide range of soil conditions. The best equation predicted root phosphatase from specific root length and soil available phosphorus content. These relationships will enable more accurate models of phosphorus control on tropical forest productivity under changing environmental conditions.

Summary

The study’s objective was to determine fine-root traits and soil measurements that influenced soil and root phosphatase activity in the soil profile. Researchers measured soil and root phosphatase to 1 m and 30 cm in soil depth, respectively, including corresponding soil conditions (phosphorus concentrations, soil texture, and bulk density) and fine-root traits (specific root length and fine-root mass density). The team found that soil phosphatase can be predicted by bulk density, organic phosphorus, and fine-root mass density and that variation in root phosphatase can be explained by available phosphorus and specific fine-root length. Thus, both fine-root traits and soil phosphorus measurements are needed to understand mechanisms, like phosphatase, that mediate phosphorus availability in tropical forests. These findings strengthen the link between phosphatase activity and existing root and soil phosphorus parameters in ecosystem models, enabling a more accurate representing of the phosphorus cycle. The study’s data merge phosphatase activity—a root and microbial function important to phosphorus acquisition—with fine-root traits and soil data, informing the understanding of phosphorus acquisition throughout the soil profile and the potential feedbacks to tropical forest growth.

Principal Investigator

Richard J. Norby
Oak Ridge National Laboratory; currently, University of Tennessee, Knoxville
rnorby@utk.edu

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
brian.benscoter@science.doe.gov

Funding

This research was supported as part of the Next Generation Ecosystem Experiments (NGEE)–Tropics project, funded by the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science.

Related Links

• Dataset Information

References