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Tropical Forests Face Increased Soil Carbon Loss Due to Climate Change
Context:
A recent study conducted by Lawrence Livermore National Laboratory (LLNL), Colorado State University, and the Smithsonian Tropical Research Institute found that climate changes could intensify soil carbon losses.
More on News:
Tropical forests, which account for more than 50% of the global terrestrial carbon sink and store nearly one-third of global soil carbon stocks, are facing a significant threat from climate change.
Carbon Dynamics and Future Projections
- Tropical forests have the shortest carbon residence time on Earth, from 6 to 15 years.
- This means that any changes in carbon inputs or outputs, such as CO2 emissions from soil, can quickly and significantly impact the carbon balance and feedback of these ecosystems.
- Future climate models predict increased warmth and dryness in the tropics, with intensified droughts and longer dry seasons, particularly in the Neotropics.
- A region stretching from southern Mexico through Central America and into northern South America, encompassing the expansive Amazon rainforest
Key Highlights:
- The research took place in Panama’s tropical forests using climate manipulation experiments that involved heating the soil by 4°C and reducing rainfall by 50%.
- Both warming and drying increased the carbon-14 content in the CO2 released from soil, which corresponds to an increase in the average age of the carbon by about 2–3 years.
- This increase indicates a greater release of “bomb” carbon (carbon-14 from underground nuclear testing circa 1963), reflecting the accelerated decomposition of older soil carbon.
- Mechanisms driving these changes differed between warming and drying.
- Warming accelerated the decomposition of older carbon by increasing CO2 emissions, which depleted newer carbon and led to a microbial shift towards using older carbon resources.
- Drying reduced the decomposition of newer carbon inputs, decreased overall soil CO2 emissions, and increased the contribution of older carbon to CO2 release due to limited delivery of fresh carbon inputs like leaf litter and roots.
Significance of Carbon-14 Analysis:
- Traditional CO2 flux measurements provide important data on overall carbon balance but are limited in revealing the underlying mechanisms.
- Carbon-14 and carbon-13 isotopes provide insights into the age of the carbon sources being metabolised and released as CO2.
- “Young” carbon is recently fixed from the atmosphere, while older carbon (decadal, century, or millennial-aged) is enriched or depleted in carbon-14 relative to the current atmosphere.