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Publication Date
12 March 2024

Plant Responses to Elevated CO2 Under Competing Hypotheses of Nitrogen and Phosphorus Limitations

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Natural terrestrial ecosystem processes, including plant biomass growth and microbial decomposition of soil organic matter, are commonly constrained by the availability of multiple nutrients. It has been widely acknowledged that high latitude ecosystems are more limited by Nitrogen (N) supply, while tropical ecosystems are strongly limited by soil Phosphorus (P) supply. However, model simulated responses of ecosystem dynamics to CO2 and nutrient perturbation remain highly uncertain, raising the question of whether models can accurately predict ecosystem carbon dynamics under future environmental changes.


This work bridges the gap between observations and model predictions, and improves the confidence in modeled carbon-climate predictions under a changing climate. Extrapolating the two prevailing nutrient limitation hypotheses (Liebig’s Law of the Minimum (LLM), Multiple Element Limitation (MEL)) to global scales using the E3SM land model, we find that the LLM and MEL significantly differ in predicting the future trajectory of ecosystem carbon accumulation. By the end of the 21st century, LLM and MEL predictions could differ by a factor of two for both vegetation and soil carbon fluxes.


Two prevailing approaches are widely applied to represent the mechanisms affecting nutrient limitations to plant growth. The LLM implies that a more limited supply of N or P in the future will dramatically dampen the rate of ecosystem carbon accumulation. The MEL approach, in which plants possess multiple pathways to overcome N and P limitation, e.g., adjustment of photosynthetic rates or investment to enhance phosphatase production or N2 fixation. In this work, we first compiled field measurements of forest N and P fertilization experiments across tropical, temperate, and boreal forest ecosystems. We then compared the LLM and MEL modeled responses of net primary production (NPP) to the applied nutrient fertilizations, and analyzed which mechanism provides a more accurate plant growth response. Finally, we evaluated the consequences of applying the two limitation approaches on future global carbon dynamics.

Point of Contact
Qing Zhu
Lawrence Berkeley National Laboratory
Funding Program Area(s)