Tropical Tree Photosynthesis and Nutrients: The Model-Data Connection

Models of phosphorus-limited tropical forests may be improved through empirical relationships between photosynthesis and nutrients.

The Science

Gas exchange and nutrient content data were collected from upper canopy leaves of 144 trees at two forest sites in Panama, differing in species composition, rainfall, and soil fertility. Relationships between photosynthesis, foliar nitrogen and phosphorus, and wood density were evaluated against mechanistic and empirical models.

The Impact

This study provides a basis for improving models of photosynthesis based on phosphorus nutrition and thereby increasing the capability of models to predict future conditions in phosphorus-limited tropical forests.

Summary

The objective of this study was to analyze and summarize data describing photosynthetic parameters and foliar nutrient concentrations from tropical forests in Panama to inform model representation of phosphorus limitation of tropical forest productivity. Gas exchange and nutrient content data were collected from upper canopy leaves of 144 trees from at least 65 species at two forest sites in Panama, differing in species composition, rainfall, and soil fertility. The relationships between photosynthetic parameters and nutrients were of similar strength for nitrogen and phosphorus and robust across diverse species and site conditions. The strongest relationship expressed maximum electron transport rate (Jmax ) as a multivariate function of both nitrogen and phosphorus, and this relationship was improved with the inclusion of independent data on wood density. Models that estimate photosynthesis from foliar nitrogen content would be improved only modestly with the inclusion of additional data on foliar phosphorus, but doing so may increase the capability of models to predict future conditions in phosphorus-limited tropical forests, especially when combined with data on edaphic conditions and other environmental drivers.

Principal Investigator

Richard Norby
Oak Ridge National Laboratory
rjn@ornl.gov

Program Manager

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

Funding

Data collection was supported by Oak Ridge National Laboratory’s Laboratory-Directed Research and Development Program. Data analysis and interpretation were supported by 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

References

Norby, R. J., L. Gu., I. C. Haworth, and A. M. Jensen, et al. "Informing models through empirical relationships between foliar phosphorus, nitrogen and photosynthesis across diverse woody species in Panama". New Phytologist 215 (4), 1425–1437  (2016). https://doi.org/10.1111/nph.14319.