Extending a land-surface model with <i>Sphagnum</i> moss to simulate responses of a northern temperate bog to whole ecosystem warming and elevated CO<sub>2</sub>

Abstract

Abstract. Mosses need to be incorporated into Earth system models to better simulate peatland functional dynamics under the changing environment. Sphagnum mosses are strong determinants of nutrient, carbon, and water cycling in peatland ecosystems. However, most land-surface models do not include Sphagnum or other mosses as represented plant functional types (PFTs), thereby limiting predictive assessment of peatland responses to environmental change. In this study, we introduce a moss PFT into the land model component (ELM) of the Energy Exascale Earth System Model (E3SM) by developing water content dynamics and nonvascular photosynthetic processes for moss. The model was parameterized and independently evaluated against observations from an ombrotrophic forested bog as part of the Spruce and Peatland Responses Under Changing Environments (SPRUCE) project. The inclusion of a Sphagnum PFT with some Sphagnum-specific processes in ELM allows it to capture the observed seasonal dynamics of Sphagnum gross primary production (GPP) albeit with an underestimate of peak GPP. The model simulated a reasonable annual net primary production (NPP) for moss but with less interannual variation than observed, and it reproduced aboveground biomass for tree PFTs and stem biomass for shrubs. Different species showed highly variable warming responses under both ambient and elevated atmospheric CO2 concentrations, and elevated CO2 altered the warming response direction for the peatland ecosystem. Microtopography is critical: Sphagnum mosses on hummocks and hollows were simulated to show opposite warming responses (NPP decreasing with warming on hummocks but increasing in hollows), and hummock Sphagnum was modeled to have a strong dependence on water table height. The inclusion of this new moss PFT in global ELM simulations may provide a useful foundation for the investigation of northern peatland carbon exchange, enhancing the predictive capacity of carbon dynamics across the regional and global scales.

Integrating Arctic Plant Functional Types in a Land Surface Model Using Above‐ and Belowground Field Observations

“…Lichens can contribute significantly to C uptake and N fixation in arctic ecosystems (Crittenden & Kershaw, 1978;Lange et al, 1998) and play important ecological roles including forming an essential part of the caribou diet in the winter (Longton, 1997). While some large-scale models have begun to integrate nonvascular PFTs and their particular traits (e.g., Druel et al, 2019;Shi et al, 2021), ELM has, until now, lacked specific capability for nonvascular arctic PFTs. In this study, bryophytes and lichens were implemented within the existing PFT framework as nonwoody plants with very low belowground biomass.…”

“…More model improvements are needed to accurately represent bryophyte and lichen physiology in ELM. To this end, Sphagnum physiological processes such as capillary wicking of water and coupling of photosynthetic rate to tissue water content are being developed in ELM for northern peatland ecosystems (Shi et al, 2021), and these developments could be incorporated into arctic bryophyte simulations in the future.…”

“…Mosses, and particularly Sphagnum spp., play important roles in high-latitude ecosystems, including buffering the soil from air temperature fluctuations and potential permafrost thaw, forming a barrier to surface water fluxes, and influencing nutrient availability and ecosystem responses to fire (Beringer et al, 2001;Blok et al, 2011;Gornall et al, 2007;Kellner, 2001;Turetsky et al, 2012 contribute significantly to C uptake and N fixation in arctic ecosystems (Crittenden & Kershaw, 1978;Lange et al, 1998) and play important ecological roles including forming an essential part of the caribou diet in the winter (Longton, 1997). While some large-scale models have begun to integrate nonvascular PFTs and their particular traits (e.g., Druel et al, 2019;Shi et al, 2021), ELM has, until now, lacked specific capability for nonvascular arctic PFTs. In this study, bryophytes and lichens were implemented within the existing PFT framework as nonwoody plants with very low belowground biomass.…”

A new approach to simulate peat accumulation, degradation and stability in a global land surface scheme (JULES vn5.8_accumulate_soil)

“…Thus the inclusion of a moss PFT and its unique functions in land surface models like JULES should be a priority, and indeed several models have done this (e.g. Porada et al (2016); Chaudhary et al (2017); Shi et al (2021)).…”

An Integrative Model for Soil Biogeochemistry and Methane Processes. II: Warming and Elevated CO2 Effects on Peatland CH4 Emissions

“…In this study, we reported on the simulating effects of warming and eCO 2 on CH 4 cycling in a northern Minnesota peatland under various warming and eCO 2 scenarios by using the ELM-SPRUCE model, a version of ELM designed for this experiment (Ricciuto et al, 2021;Shi et al, 2015Shi et al, , 2021. As the second in a series of two modeling papers, we expanded upon the model description provided by Ricciuto et al (2021) and explored the warming and eCO 2 impacts on CH 4 cycling and further compared the simulated processes against observational data obtained from a global meta-analysis.…”