Does elevated atmospheric CO₂affect soil carbon burial and soil weathering in a forest ecosystem?

Abstract

Most experimental studies measuring the effects of climate change on terrestrial C cycling have focused on processes that occur at relatively short time scales (up to a few years). However, climate-soil C interactions are influenced over much longer time scales by bioturbation and soil weathering affecting soil fertility, ecosystem productivity, and C storage. Elevated CO2can increase belowground C inputs and stimulate soil biota, potentially affecting bioturbation, and can decrease soil pH which could accelerate soil weathering rates. To determine whether we could resolve any changes in bioturbation or C storage, we investigated soil profiles collected from ambient and elevated-CO2plots at the Free-Air Carbon-Dioxide Enrichment (FACE) forest site at Oak Ridge National Laboratory after 11 years of 13C-depleted CO2 release. Profiles of organic carbon concentration, δ13C values, and activities of 137Cs, 210Pb, and 226Ra were measured to ∼30 cm depth in replicated soil cores to evaluate the effects of elevated CO2 on these parameters. Bioturbation models based on fitting advection-diffusion equations to 137Cs and 210Pb profiles showed that ambient and elevated-CO2 plots had indistinguishable ranges of apparent biodiffusion constants, advection rates, and soil mixing times, although apparent biodiffusion constants and advection rates were larger for 137Cs than for 210Pb as is generally observed in soils. Temporal changes in profiles of δ13C values of soil organic carbon (SOC) suggest that addition of new SOC at depth was occurring at a faster rate than that implied by the net advection term of the bioturbation model. Ratios of (210Pb/226Ra) may indicate apparent soil mixing cells that are consistent with biological mechanisms, possibly earthworms and root proliferation, driving C addition and the mixing of soil between ∼4 cm and ∼18 cm depth. Burial of SOC by soil mixing processes could substantially increase the net long-term storage of soil C and should be incorporated in soil-atmosphere interaction models.

Greenhouse gas emissions from riparian zone cropland in a tributary bay of the Three Gorges Reservoir, China

“…Cumulative fluxes of GHGs (Table 5) showed that CO 2 emission dominated the GHG fluxes when the CH 4 and N 2 O fluxes were calculated as CO 2 equivalents during the growing season, which is comparable to the results archived in Audet et al (2013) and Zhou et al (2017). Litter from soil surface, root residues and exudates in splits are the main source of soil organic matter in terrestrial ecosystems (Gleixner, 2005;Gonzalez-Meler et al, 2018). The high organic matter in riparian soil along with water level fluctuation created slow decomposition of external organic matter and microorganisms (Schimel et al, 2011), and insoluble organic carbon transferred to inorganic carbon through mineralization resulting in the increase of CO 2 emissions (Andrews & Schlesinger, 2001).…”

Peer Review #1 of "Greenhouse gas emissions from riparian zone cropland in a tributary bay of the Three Gorges Reservoir, China (v0.1)"

“…Cumulative fluxes of GHGs (Table 5) showed that CO 2 emission dominated the GHG fluxes when the CH 4 and N 2 O fluxes were calculated as CO 2 equivalents during the growing season, which is comparable to the results archived in Aude et al 2013and Zhou et al (2017). Litter from soil surface, root residues and exudates in splits are the main source of soil organic matter in terrestrial ecosystems (Gleixner et al, 2005;Gonzalez-Meler et al, 2018 ).The high organic matter in riparian soil along with water level fluctuation created slow decomposition of external organic matter and microorganisms (Schimel et al, 2011), and insoluble organic carbon transferred to inorganic carbon through mineralization resulting in the increase of CO 2 emissions (Andrews &Schlesinger, 2001). Soil TC and DOC in croplands were lower than in grass fields (Table 3), probably due to the intensive interference of anthropogenic activities in cropland which may loosen the soil, increase the soil permeability, and hence lead to the easy run-off of soil DOC (Wang et al, 2005).…”

Deeper snow increases the net soil organic carbon accrual rate in moist acidic tussock tundra:210Pb evidence from Arctic Alaska

“…We measured and compared profiles of soil organic carbon and 210 Pb (half-life = 22.3 a) along with 7 Be (half-life = 53.3 d), 137 Cs (half-life = 30.2 a), and 241 Am (half-life = 432.2 a) in a set of active layer cores from within and outside the area influenced by a twenty-two-year snow fence experiment. This was a reconnaissance study conducted with a relatively small set of cores to assess whether this approach could give meaningful results over a decadal timescale, given the known complications of 210 Pb-based soil chronology Münnich 1989, 1991;Kaste, Heimsath, and Bostick 2007;Kaste et al 2011;Landis, Renshaw, and Kaste 2016;Olid et al 2016;Gonzalez-Meler et al 2018). Our objective was to ascertain the impact of deeper winter snow accumulation (caused by the snow fence) on the net rate of soil organic carbon accumulation.…”

“…Applications of fallout radionuclides in studies of sediment, soil, and peat accumulation ( 7 Be, 137 Cs, 210 Pb, 241 Am) have been explored by a number of authors (Robbins and Edgington 1975;Münnich 1989, 1991;Urban et al 1990;Kaste, Heimsath, and Bostick 2007;Kaste et al 2011;Abril and Gharbi 2012;Kaste 2014, 2016;Shotyk et al 2015;Olid et al 2016;Davies et al 2018;Gonzalez-Meler et al 2018). The prior studies most relevant to the current study are those dealing with accumulation of soil and peat.…”