Temperature Thresholds of Pyrogenic Dissolved Organic Matter in Heating Experiments Simulating Forest Fires

Area of Science:

• Environmental Chemistry
• Soil Science
• Organic Geochemistry

Background:

• Forest fires generate pyrogenic dissolved organic matter (DOM), influencing soil properties.
• Heating temperature (HT) is a key factor, but component-specific thresholds for DOM production and loss are unknown.

Purpose of the Study:

• To identify temperature thresholds for maximum DOM production (TTmax) and net DOC loss (TT0) on a component-specific basis.
• To analyze DOM compositional changes with varying HT in detritus and soil.

Main Methods:

• Solid-state 13C nuclear magnetic resonance spectroscopy
• Absorbance and fluorescence spectroscopies
• Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS)
• Analysis of DOM from detritus and soil heated from 150-500 °C

Main Results:

• TTmax for bulk dissolved organic carbon (DOC) and most DOM components ranged from 225-250 °C in both detritus and soil.
• TT0 was consistently lower in detritus than in soil.
• Different DOM components exhibited distinct temperature thresholds for net loss, starting with carbohydrates/aliphatics, followed by proteins/polyphenolics, and finally condensed aromatics.
• Burning below TT0, especially at TTmax, increased DOC quantity, potentially enhancing labile substrates for microbes.

Conclusions:

• Wildfire impacts on soil organic matter are nonlinear and depend on temperature and DOM component.
• Understanding component-specific temperature thresholds is crucial for predicting post-fire soil organic matter dynamics and ecosystem recovery.