Negative Feedback by Vegetation on Soil Organic Matter Decomposition in a Coastal Wetland

Abstract

There has been much debate about the external drivers that affect the decomposition of soil organic matter (SOM). Particularly, the feedback mechanisms between SOM and mineral weathering are poorly understood. We used the cotton strip assay combined with measurements of water table, pore water salinity, and soil properties along a landscape-scale gradient to study these mechanisms. The results revealed that cotton tensile strength loss (CTSL) rates ranged from 2.0% day−1 to 4.6% day−1 and varied significantly among sites and depths. A multiple regression model revealed that the corelation between the CTSL and submersion duration (SD) was positive when the chemical index of alteration (CIA) was ~65% and negative over most of the range of SD when the CIA was ~45%. The results suggest that the hydrological conditions induced by tidal effects endanger the stocks of carbon sequestered in coastal wetland soils. However, sites with CTSL rates as high as 4.0–5.0% day−1 tended to gain more nutrients than sites with lower CTSL rates. The fixation of atmospheric CO2 via plant growth may therefore be stimulated in coastal wetland soils by the recycling of mineral nutrients via enhanced weathering. The result is a negative feedback of the ecotone on SOM decomposition.