Nitrogen and Phosphorus Pools and Turnover in Peat Following 5 Years of Simulated Climate Change
Authors
Verity G. Salmon* (salmonvg@ornl.gov), Joanne Childs, Geoff Schwaner, Colleen M. Iversen, Paul Hanson, Melanie Mayes, Daniel Ricciuto
Institutions
Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN
URLs
Abstract
Boreal peatlands currently store large amounts of carbon (C) and will be exposed to higher temperatures and elevated levels of atmospheric carbon dioxide (eCO2) in the coming decades. The Spruce and Peatland Under Changing Environments (SPRUCE) experimental site in northern Minnesota is a forested, ombrotrophic bog that has been subjected to experimental warming and eCO2 treatments since 2016. In 2021, the team sampled the top 30 cm of the peat at SPRUCE and began a year-long laboratory incubation to assess pool sizes and turnover of C, nitrogen (N) and phosphorous (P) in the rhizosphere. Mineralization of C, N, and P was quantified by measuring carbon dioxide (CO2), N2O, and methane (CH4) gas fluxes as well as NH4, NO3, and PO4 in soil leachate. The optimized decomposition conditions and extended timeframe of the laboratory incubation meant that total mineralization cumulative mineralization curves fit with exponential decay models could be explored for the three elements. Preliminary results from this experiment indicate that 5 years of experimental field manipulations have significantly impacted pool sizes and cumulative mineralization of these critical elements in the rhizosphere. Total CO2 mineralized significantly decreased with field temperature and, in surface soils, slower CO2 mineralization was explained by a higher proportion of soil C being present in an inactive versus active cycling C pool. The bulk %N of incubated peat increased broadly with depth (p=0.09) but notably increased with field temperature (p=0.01). Total NH4 mineralization significantly increased with field temperature and this increase was greater than expected based on the higher bulk soil %N alone. Total PO4 mineralization was not impacted by the experimental treatments. These findings indicate that C, N, and P cycling in warmed rhizosphere at SPRUCE has become uncoupled during the first 5 years of experimental warming due to actively cycling C being lost and peat N being found in more readily mineralized forms.