Journal Article

Causal mechanisms of soil organic matter decomposition: deconstructing salinity and flooding impacts in coastal wetlands

Schoolmaster, Donald R., Stagg, Camille L., Cormier, Nicole, Krauss, Ken W., Conner, William H.

2017

Overview

Coastal wetlands significantly contribute to global carbon storage potential. Sea-level rise and other climate-change-induced disturbances threaten coastal wetland sustainability and carbon storage capacity. It is critical that we understand the mechanisms controlling wetland carbon loss so that we can predict and manage these resources in anticipation of climate change. However, our current understanding of the mechanisms that control soil organic matter decomposition, in particular the impacts of elevated salinity, are limited, and literature reports are contradictory. In an attempt to improve our understanding of these complex processes, we measured root and rhizome decomposition and developed a causal model to identify and quantify the mechanisms that influence soil organic matter decomposition in coastal wetlands that are impacted by sea-level rise. We identified three causal pathways: (1) a direct pathway representing the effects of flooding on soil moisture, (2) a direct pathway representing the effects of salinity on decomposer microbial communities and soil biogeochemistry, and (3) an indirect pathway representing the effects of salinity on litter quality through changes in plant community composition over time. We used this model to test the effects of alternate scenarios on the response of tidal freshwater forested wetlands and oligohaline marshes to short- and long-term climate-induced disturbances of flooding and salinity. In tidal freshwater forested wetlands, the model predicted less decomposition in response to drought, hurricane salinity pulsing, and long-term sea-level rise. In contrast, in the oligohaline marsh, the model predicted no change in response to drought and sea-level rise, and increased decomposition following a hurricane salinity pulse. Our results show that it is critical to consider the temporal scale of disturbance and the magnitude of exposure when assessing the effects of salinity intrusion on carbon mineralization in coastal wetlands. Here, we identify three causal mechanisms that can reconcile disparities between long-term and short-term salinity impacts on organic matter decomposition.

• Publisher: Wiley Subscription Services, Inc,Ecological Society of America
• Subject: Biogeochemistry / botanical composition / Carbon / Carbon sequestration / causal model / Climate / Climate change / climatic factors / Coastal environments / Community composition / Composition effects / CONCEPTS & SYNTHESIS: EMPHASIZING NEW IDEAS TO STIMULATE RESEARCH IN ECOLOGY / Decomposition / Disturbances / Drought / Flood predictions / Flooding / Floods / Forested wetlands / Fresh Water / freshwater / hurricane / Hurricanes / Intrusion / Litter / lowland forests / Marshes / Mathematical models / Microbial activity / microbial communities / Microorganisms / Mineralization / oligohaline marsh / Organic matter / Organic soils / Plant communities / rhizomes / Salinity / Salinity effects / Sea level / Sea level rise / Soil - chemistry / Soil moisture / Soil organic matter / soil water / Soils / Storage capacity / structural equation model / tidal freshwater forested wetlands / Wetlands