Review status: a revised version of this preprint was accepted for the journal BG and is expected to appear here in due course.
Representing methane emissions from wet tropical forest soils using microbial functional groups constrained by soil diffusivity
Debjani Sihi1,Xiaofeng Xu2,Mónica Salazar Ortiz3,Christine S. O'Connell4,5,Whendee L. Silver5,Carla López-Lloreda6,Julia M. Brenner1,Ryan K. Quinn1,7,Jana R. Phillips1,Brent D. Newman8,and Melanie A. Mayes1Debjani Sihi et al.Debjani Sihi1,Xiaofeng Xu2,Mónica Salazar Ortiz3,Christine S. O'Connell4,5,Whendee L. Silver5,Carla López-Lloreda6,Julia M. Brenner1,Ryan K. Quinn1,7,Jana R. Phillips1,Brent D. Newman8,and Melanie A. Mayes1
Received: 12 Jun 2020 – Accepted for review: 20 Jul 2020 – Discussion started: 29 Jul 2020
Abstract. Tropical ecosystems contribute significantly to global emissions of methane (CH4) and landscape topography influences the rate of CH4 emissions from wet tropical forest soils. However, extreme events such as drought can alter normal topographic patterns of emissions. Here we explain the dynamics of CH4 emissions during normal and drought conditions across a catena in the Luquillo Experimental Forest, Puerto Rico. Valley soils served as the major source of CH4 emissions in a normal precipitation year (2016), but drought recovery in 2015 resulted in dramatic pulses in CH4 emissions from all topographic positions. Geochemical parameters including dissolved organic carbon (C) (ridge ≫ slope ≫ valley), acetate (ridge ≥ slope > valley), and soil pH (valley ≫ slope ≫ ridge), and meteorological parameters like soil moisture (valley > slope = ridge) and oxygen (O2) concentrations (slope = ridge > valley) varied across the catena. During the drought, soil moisture decreased in the slope and ridge and O2 concentrations increased in the valley. We simulated the dynamics of CH4 emissions with the Microbial Model for Methane Dynamics-Dual Arrhenius and Michaelis Menten (M3D-DAMM) which couples a microbial functional group CH4 model with a diffusivity module for solute and gas transport within soil microsites. Contrasting patterns of soil moisture, O2, acetate, and associated changes in soil pH with topography regulated simulated CH4 emissions, but emissions were also altered by rate-limited diffusion in soil microsites. Changes in simulated available substrate for CH4 production (acetate, CO2, and H2) and oxidation (O2 and CH4) increased the predicted biomass of methanotrophs during the drought event and methanogens during drought recovery, which in turn affected net emissions of CH4. A variance-based sensitivity analysis suggested that parameters related to acetotrophic methanogenesis and methanotrophy were most critical to simulate net CH4 emissions. This study enhanced the predictive capability for CH4 emissions associated with complex topography and drought in wet tropical forest soils.
Humid tropical soils are important sources and sinks of methane. We used model simulation to understand how different kinds of microbes and observed soil moisture and oxygen dynamics contribute to production and consumption of methane along a wet tropical hillslope during normal and drought conditions. Drought alters the diffusion of oxygen and microbial substrates into and out of soil microsites, resulting in enhanced methane release from the entire hillslope during drought recovery.
Humid tropical soils are important sources and sinks of methane. We used model simulation to...