Soil Solution Viscosity Reduces CO2 Emissions in Tropical Soils: Implications for Climate Change Mitigation

Soil CO2 emissions, driven primarily by microbial respiration, represent a major component of terrestrial carbon flux and play a crucial role in global climate change. Although several soil physicochemical factors regulating microbial activity are well known, the role of soil solution viscosity remains largely unexplored. This study evaluated how polyethylene glycol (PEG6000)-induced increases in soil solution viscosity affect microbial activity-derived CO2 emissions in a Rhodic Ferralsol (eutric). Three concentrations of PEG6000 (50, 75, and 100 g L−1), corresponding to viscosities of 1.93, 2.76, and 3.88 cP, respectively, were compared to a water-based control (1.11 cP). Soil CO2 emissions, soil O2 capture, temperature, and water content were measured over a 60-day period using standard methods. Results showed significant reductions in cumulative CO2 emissions of 20%, 25%, and 12% for PEG6000 treatments, respectively, compared to the control. Decreased O2 capture at viscosities of 1.93 and 2.76 cP (50 and 75 g L−1, respectively) indicated reduced microbial activity. These findings reveal a previously underappreciated biophysical mechanism regulating soil carbon emissions. Understanding and managing soil solution viscosity could offer a novel strategy to mitigate CO2 emissions in tropical soils, thus contributing to climate change mitigation and sustainable soil management, particularly in highly weathered tropical ecosystems.