Plants across the globe are now believed to absorb around 31% more carbon dioxide than previously estimated, as indicated by a recent study. This research is anticipated to enhance the Earth system simulations utilized by scientists to forecast future climate changes, highlighting the crucial role of natural carbon sequestration in managing greenhouse gases.
A new assessment from scientists reveals that plants worldwide are capturing approximately 31% more carbon dioxide than was originally thought. This research, published in the journal Nature, is expected to refine Earth system simulations that scientists depend on for predicting future climatic conditions, emphasizing the significance of natural carbon capture for mitigating greenhouse gas emissions.
The process by which land plants extract CO2 from the atmosphere through photosynthesis is termed Terrestrial Gross Primary Production (GPP). This process represents the largest exchange of carbon between the land and the atmosphere globally. GPP is typically measured in petagrams of carbon per year, with one petagram equivalent to one billion metric tons, approximately the CO2 produced annually by 238 million gasoline-powered cars.
A group of researchers from Cornell University, in collaboration with the Department of Energy’s Oak Ridge National Laboratory, employed new models and measurements to estimate GPP from land at 157 petagrams of carbon per year, an increase from the previous estimate of 120 petagrams made 40 years ago, which is still used in most carbon cycle assessments. Their findings are documented in the paper titled “Terrestrial Photosynthesis Inferred from Plant Carbonyl Sulfide Uptake.”
The researchers developed a comprehensive model that tracks carbonyl sulfide (OCS) from the atmosphere into the chloroplasts of leaves, where photosynthesis occurs. They quantified photosynthetic activity by monitoring OCS, which takes a path similar to CO2 within a leaf and is more straightforward to measure than CO2 diffusion. For these reasons, OCS is utilized as a proxy for photosynthesis at both the plant and leaf levels. This study demonstrated that OCS is an effective measure for estimating photosynthesis on larger scales over extended periods, making it a reliable indicator of global GPP.
The team utilized plant data from multiple sources to aid the model’s development, including the LeafWeb database, created at ORNL to support the Department of Energy’s Terrestrial Ecosystem Science Scientific Focus Area (TES-SFA). LeafWeb compiles photosynthetic trait data from scientists worldwide to enhance carbon cycle modeling. The researchers validated their model results by comparing them with high-resolution data from environmental monitoring towers, avoiding potential satellite data complications caused by cloud cover, particularly in tropical regions.
A significant contributor to the revised estimate is an improved understanding of a process known as mesophyll diffusion, which describes how OCS and CO2 move from leaves into chloroplasts for carbon fixation. Grasping mesophyll diffusion is vital for assessing how effectively plants perform photosynthesis and adapt to changing environments.
Co-author Lianhong Gu, a specialist in photosynthesis and distinguished staff scientist at ORNL’s Environmental Sciences Division, played a pivotal role in developing the mesophyll conductance model, which numerically illustrates the diffusion of OCS within leaves and its connection to photosynthesis.
Gu commented, “Determining the annual CO2 fixation by plants has been a complex challenge for scientists for some time. The initial estimate of 120 petagrams per year was made in the 1980s, and it persisted as we explored new methodologies. Accurately gauging global GPP is essential since initial land carbon uptake influences our broader assessments of Earth’s carbon cycle.”
“It is crucial to ensure that fundamental processes in the carbon cycle are adequately represented in larger-scale models,” Gu further stated. “For Earth-scale simulations to be effective, they must accurately depict the processes involved. This work marks a significant advancement in establishing a definitive number.”
Research indicated that pan-tropical rainforests contributed the most significant difference between prior estimates and the new figures, a finding supported by ground data, according to Gu. This revelation suggests that rainforests serve as a more substantial natural carbon sink than what satellite data previously indicated.
Understanding how much carbon can be captured by land ecosystems, particularly forests with their extensive biomass, is critical for predicting future climate changes.
“Pinpointing our GPP estimates using dependable global observations is vital for enhancing our predictions of future atmospheric CO2 levels and the implications for global climate,” explained Peter Thornton, Corporate Fellow and lead of the Earth Systems Science Section at ORNL.
The outcomes of this study underline the need to incorporate essential processes, such as mesophyll conductance, into photosynthesis model representations. The Department of Energy’s Next Generation Ecosystem Experiments in the Tropics aim to improve model predictions regarding tropical forest responses to climate change. These findings can guide new model developments aimed at reducing uncertainties in tropical forest GPP predictions.
Collaborating with Cornell’s School of Integrative Plant Sciences on this project were Wageningen University and Research from The Netherlands, the Carnegie Institution for Sciences, Colorado State University, the University of California Santa Cruz, and the NASA Jet Propulsion Laboratory.
Funding was provided by Cornell, the National Science Foundation, and the ORNL TES-SFA, supported by the Department of Energy’s Office of Science Biological and Environmental Research program.
