Check out our latest paper on the mineralization of soil organic matter in coastal wetlands. Coastal wetlands are mangrove forests and salt marshes at the interface where land meets the sea. Mangrove forests are located in the tropics, salt marshes with primarily herbaceous vegetation are found at cooler latitudes, and the two habitat types intergrade in the subtropics. These ecosystems store massive amounts of soil organic matter, the decaying remains of once-living material. The mineralization (i.e., complete decomposition) of this organic matter results in the loss of soil mass and a decline in soil elevation, rendering these ecosystems more vulnerable to sea level rise; releases carbon- and nitrogen-based greenhouse gases and pollutants to air and seawater; and yet supplies nutrients to coastal wetland vegetation.
Given these important roles played by soil organic matter mineralization, we are interested in how mineralization in Florida’s subtropical coastal wetlands might respond to climate change. Climate change results in sea level rise and an increase in coastal soil inundation, warming, and the redistribution of plant species (the encroachment of mangrove forests into herbaceous salt marshes). An understanding of how climate change might affect organic matter mineralization must account for the response of mineralization to these three factors: increased tidal inundation (which should increase anoxia that suppresses mineralization), warming (which should stimulate mineralization), and changes in the plant species that produce organic matter.
Our new paper investigates how these factors interactively affect carbon (C) and nitrogen (N) mineralization in coastal wetland soils. Using both a field survey and laboratory experiment, we found C mineralization was increased by warming, but suppressed by soil saturation and prolonged inundation. However, C mineralization in inundated soil was extraordinarily sensitive to temperature, so the stimulation of C mineralization by warming may “win out” over the protection of soil C by prolonged inundation and soil saturation. Ecosystem type was important, too, as mangrove forest soil had higher “carbon quality” (more mineralization for a given amount of organic matter), while N mineralization was higher in salt marshes. The take-home message is that C and N mineralization in coastal wetlands will change with the alterations in soil water regime, temperature, and plant composition that accompany climate change.