Journal Article

Flexible Foliar Stoichiometry Reduces the Magnitude of the Global Land Carbon Sink

Bonan, Gordon B., Cleveland, Cory C., Wieder, William R., Hauser, Emma

2023

Overview

Increased plant growth under elevated carbon dioxide (CO2) slows the pace of climate warming and underlies projections of terrestrial carbon (C) and climate dynamics. However, this important ecosystem service may be diminished by concurrent changes to vegetation carbon‐to‐nitrogen (C:N) ratios. Despite clear observational evidence of increasing foliar C:N under elevated CO2, our understanding of potential ecological consequences of foliar stoichiometric flexibility is incomplete. Here, we illustrate that when we incorporated CO2‐driven increases in foliar stoichiometry into the Community Land Model the projected land C sink decreased two‐fold by the end of the century compared to simulations with fixed foliar chemistry. Further, CO2‐driven increases in foliar C:N profoundly altered Earth's hydrologic cycle, reducing evapotranspiration and increasing runoff, and reduced belowground N cycling rates. These findings underscore the urgency of further research to examine both the direct and indirect effects of changing foliar stoichiometry on soil N cycling and plant productivity. Plain Language Summary As atmospheric carbon dioxide (CO2) increases, plants grow more and take up more CO2, which could slow the pace of climate change. However, higher CO2 dilutes leaf nutrient concentrations, which could ultimately limit plant growth as CO2 continues to rise. The change in leaf chemistry in response to rising CO2 is not well represented in models used to predict future productivity and the land carbon sink. By simulating CO2‐driven changes in leaf chemistry in the Community Land Model, we quantified potential effects of shifting leaf chemistry on future vegetation growth and global C, nutrient, and hydrologic cycles. The new model simulation reduced the strength of the land C sink 2‐fold compared to simulations where foliar chemistry does not change in response to atmospheric CO2. The reduction in plant growth also produced large hydrologic changes, including reduced global evapotranspiration and increased runoff. Nitrogen cycling rates were reduced in the flexible simulation but highlighted a gap in our understanding of aboveground‐belowground feedbacks that warrants further research. Thus, the ways we represent foliar chemistry in models are important for understanding the future conditions of the planet and our capacity to respond to climate change. Key Points A flexible, CO2‐driven parameterization of foliar C:N in the Community Land Model produced a 2‐fold reduction in the projected land C sink The flexible foliar C:N parameterization also had large effects on the hydrologic cycle, reducing evapotranspiration and increasing runoff N cycling rates were reduced under the flexible C:N scenario but highlight the need for additional research on modeled plant‐soil feedbacks

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: biogeochemical cycling / Biogeochemistry / Carbon dioxide / Carbon sinks / Climate / Climate change / Community Land Model / Ecological effects / Ecosystem services / elevated CO2 / Evapotranspiration / Global warming / Hydrologic cycle / Hydrological cycle / land C sink / Nitrogen / Plant growth / Simulation / Stoichiometry / Terrestrial ecosystems / Vegetation