Phenolic Compounds and Black Carbon Feedback Controls on Peat Decomposition and Carbon Accumulation in Southeastern Peat

Earth System Models (ESMs) predict increased frequency of extreme wet and dry periods in the subtropics and tropics over the next century, resulting in uncertain carbon (C) budgets and greenhouse gases (GHG) fluxes. Globally, approximately 1/3 of peat stores are found in subtropical and tropical peatlands (STPs) formed from high-lignin woody biomass. These peatlands have persisted through changing climate and sea level over the last 4000 years and continue to accrete peat along the Atlantic coast from Virginia/North Carolina (VA/NC), to Florida (FL) to tropical Panama (PN), even under climate driven conditions of drought, warmer temperatures and fire. Our questions are: 1) why do these stressed non-Sphagnum subtropical and tropical peatlands continue to accumulate C, and 2) what insights can we gain from studying their natural processes and control mechanisms. We propose a 3-year experimental comparison across STPs to reveal the key process-level mechanisms controlling soil C stabilization, accumulation, and long-term carbon storage. Our main hypothesize is that STPs native-fire-adapted shrubs/trees communities produce higher polyphenol containing litter than Sphagnum/Carex communities. Polyphenols are secondary metabolites of plants involved in defense against ultraviolet radiation or attack by pathogens. High concentrations in plant tissues also prevent microbial decay of litter resulting in buildup of recalcitrant (decay resistant) organic matter in the soil and leading to the formation and long-term storage of peat. This storage difference, in conjunction with climate induced regimes of frequent low-intensity fire, creates refractory decomposition-resistant peat by a dual “latch key mechanism” consisting of high phenol and Black Carbon (i.e., the BC complex from fire forms decay resistant aromatics). Together these retardants reduce GHG flux, and C decomposition of STPs peats even under altered hydrologic conditions, higher temperatures and drought.

Objectives:

I: Identify and compare process-level mechanisms controlling peat accretion and C losses from Sphagnum-spruce bog sites in MN, shrub-bogs in NC, subtropical sawgrass-shrub peats in the FL Everglades, to tropical Wax Myrtle-Titi shrub bogs in PN. This never-before-studied latitudinal gradient will allow experimental quantification of biotic (plants type) and abiotic (low-intensity fire and drought) contributions to resultant high phenol/low carbon quality litter and specific BC aromatics;

II: Assess the composition and origin of aromatic compounds in peat and porewater at the molecular level and the importance of fire derived aromatic compounds limiting peat decomposition using multiple advanced analytical chemistry techniques.

Anticipated Outcomes:

This research provides the first major latitudinal comparative analysis of peatland C chemistry, tests a new dual control model for sustaining C, incorporates advanced analytical methods and comprehensive C chemistry data, and uses these data for modeling in support of DOE’s climate change research program and ESMs.