Amazon Forest Response to CO2 Fertilization Dependent on Plant Phosphorus Acquisition

The Science

Plant growth is dependent on the availability of nutrients such as nitrogen, phosphorous, and potassium in the soil. Despite the importance of phosphorous in plant processes (e.g., growth and photosynthesis), global Earth system models used in the Coupled Model Intercomparison Project (CMIP5) have not previously included the effects of its availability in studying the global carbon cycle. This study shows that phosphorus availability could greatly reduce the projected CO₂-induced carbon sink in Amazon rainforests. This study suggests that the Amazon rainforest response to increasing atmospheric CO₂ depends on the ability of trees to upregulate phosphorus acquisition in response to increased carbon availability.

The Impact

Currently, CMIP5 models predict that Amazon rainforests will continue to act as carbon sinks in the future due to the CO₂ fertilization effect. However, the role of phosphorus availability (which is impoverished across the Amazon Basin yet controls forest functioning) has not been considered within CMIP5 simulations. This study suggests that the CMIP5 predicted carbon sink would likely be much less due to phosphorus limitation, suggesting that Amazon rainforests may be less resilient to climate change than previously assumed.

Summary

An ensemble of 14 terrestrial ecosystem models was used to simulate the planned free-air CO₂ enrichment experiment, AmazonFACE. Model simulations showed that phosphorus availability reduced the projected CO₂– induced carbon sink by about 50% compared to estimates from models assuming no phosphorus limitation.

Large variations in ecosystem responses to elevated CO₂ among phosphorous-enabled models (ranging from 5 to 140 g C m^–2 yr^–2 in biomass carbon response) are mainly due to contrasting representations of plant phosphorus use and acquisition strategies among models. This study highlights the importance of phosphorus acquisition and use, including alternative strategies, in Amazon rainforest responses to increasing atmospheric CO₂ concentration.

Funding

DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments (NGEE)–Tropics and Energy Exascale Earth System Model (E3SM) programs.

References

Fleischer, K., A. Rammig, M. G. De Kauwe, A. P. Walker, T. F. Domingues, L. Fuchslueger, S. Garcia, D. Goll, A. Grandis, M. Jiang, V. E. Haverd, F. Hofhansl, J. Holm, B. Kruijt, F. Leung, B. Medlyn, L. M. Mercado, R. J. Norby, B. C. Pak, B. Quesada, C. von Randow, K. Schaap, O. Valverde-Barrantes, Y. Wang, X. Yang, S. Zaehle, Q. Zhu, and D. Lapola. “Amazon forest responses to CO₂ fertilization dependent on plant phosphorus acquisition.” Nature Geoscience 12, 736–41 (2019). DOI:10.1038/s41561-019-0404-9