Decomposition of soil organic matter due to dessication of high elevation meadow soils

Background/Question/Methods

The cyclic drawdown/recharge of the water table that exists in most peatland systems impose important controls on organic matter storage and decomposition as well as soil physical properties.  The normally saturated soils function to reduce the aerobic decomposition and allow organic matter to accumulate over time, which increases the ability of these systems to retain water. However, during dry years, there is potential for peatland systems to dessicate, allowing decomposition to proceed at a faster rate than normal. In order to better understand how high elevation wetlands will respond to increasingly dry years, we incubated meadow soils collected along a hydrologic gradient at three different depths at 5 different water potentials and measured the CO₂ flux at intervals for over one year to determine if dessication of meadow soils influences cumulative carbon flux. 

Results/Conclusions

Contrary to what was expected, we found that the cumulative carbon mineralization was greatest at the highest (0.1 bar) and lowest (4 bar) water potential, across all regions of the meadow. We propose a conceptual model that illustrates how compaction of organic matter rich soils during drydown leads to rapid loss of soil carbon that was previously physically protected from oxidative decomposition.