scholarly journals The contribution of deadwood to soil carbon dynamics in contrasting temperate forest ecosystems

2021 ◽  
Author(s):  
V. L. Shannon ◽  
E. I. Vanguelova ◽  
J. I. L. Morison ◽  
L. J. Shaw ◽  
J. M. Clark
Keyword(s):  
Organic Carbon ◽  
Soil Carbon ◽  
Leaf Litter ◽  
Phenol Oxidase ◽  
Forest Carbon ◽  
Microbial Decomposition ◽  
High Background ◽  
Soil C ◽  
Tea Bag Index ◽  
Water Extractable Organic Carbon

AbstractDeadwood forms a significant carbon pool in forest systems and is a potential source of dissolved organic carbon (DOC) input to soil, yet little is known about how deadwood effects forest soil carbon cycling. Deadwood DOC inputs to soil may be retained through sorption or may prime microbial decomposition of existing organic matter to produce additional DOC. To determine impacts of deadwood on soil C cycling, we analysed surface soil from beneath deadwood or leaf litter only, along chronosequences of stands of lowland oak and upland Sitka spruce. The concentration and quality (by optical indices) of water-extracted soil DOC (water-extractable organic carbon; WEOC), in situ decomposition ‘tea bag index’ (TBI) parameters and enzymatic potential assays (β-D-cellubiosidase, β-glucosidase, β-xylosidase, leucine aminopeptidase, phosphatase, phenol oxidase) were determined. Presence of deadwood significantly (p < 0.05) increased WEOC concentration (~ 1.5 to ~ 1.75 times) in the mineral oak soil but had no effect on WEOC in spruce soils, potentially because spruce deadwood DOC inputs were masked by a high background of WEOC (1168 mg kg−1 soil) and/or were not retained through mineral sorption in the highly organic (~ 90% SOM) soil. TBI and enzyme evidence suggested that deadwood-derived DOC did not impact existing forest carbon pools via microbial priming, possibly due to the more humified/aromatic quality of DOC produced (humification index of 0.75 and 0.65 for deadwood and leaf litter WEOC, respectively). Forest carbon budgets, particularly those for mineral soils, may underestimate the quantity of DOC if derived from soil monitoring that does not include a deadwood component.

scholarly journals The undetected loss of aged carbon from boreal mineral soils

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Geert Hensgens ◽  
Hjalmar Laudon ◽  
Mark S. Johnson ◽  
Martin Berggren
Keyword(s):  
Organic Carbon ◽  
Boreal Forest ◽  
Soil C ◽  
Earth Systems ◽  
Nuclear Bomb ◽  
C Cycle ◽  
Water Extractable Organic Carbon ◽  
High Lability ◽  
Mineral Soils ◽  
Terrestrial Biomes

AbstractThe boreal forest is among the largest terrestrial biomes on earth, storing more carbon (C) than the atmosphere. Due to rapid climatic warming and enhanced human development, the boreal region may have begun transitioning from a net C sink to a net source. This raises serious concern that old biogenic soil C can be re-introduced into the modern C cycle in near future. Combining bio-decay experiments, mixing models and the Keeling plot method, we discovered a distinct old pre-bomb organic carbon fraction with high biodegradation rate. In total, 34 ± 12% of water-extractable organic carbon (WEOC) in podzols, one of the dominating boreal soil types, consisted of aged (~ 1000 year) labile C. The omission of this aged (i.e., Δ14C depleted) WEOC fraction in earlier studies is due to the co-occurrence with Δ14C enriched modern C formed following 1950s nuclear bomb testing masking its existence. High lability of aged soil WEOC and masking effects of modern Δ14C enriched C suggests that the risk for mobilization and re-introduction of this ancient C pool into the modern C cycle has gone undetected. Our findings have important implications for earth systems models in terms of climate-carbon feedbacks and the future C balance of the boreal forest.

scholarly journals Examining soil carbon uncertainty in a global model: response of microbial decomposition to temperature, moisture and nutrient limitation

2013 ◽  
Vol 10 (6) ◽  
pp. 10229-10269
Author(s):  
J.-F. Exbrayat ◽  
A. J. Pitman ◽  
Q. Zhang ◽  
G. Abramowitz ◽  
Y.-P. Wang
Keyword(s):  
Soil Carbon ◽  
Nutrient Limitation ◽  
Historical Change ◽  
Cmip5 Models ◽  
Earth System ◽  
Microbial Decomposition ◽  
Soil C ◽  
System Models ◽  
C And N ◽  
Earth System Models

Abstract. Reliable projections of future climate require land–atmosphere carbon (C) fluxes to be represented realistically in Earth System Models. There are several sources of uncertainty in how carbon is parameterized in these models. First, while interactions between the C, nitrogen (N) and phosphorus (P) cycles have been implemented in some models, these lead to diverse changes in land–atmosphere fluxes. Second, while the parameterization of soil organic matter decomposition is similar between models, formulations of the control of the soil physical state on microbial activity vary widely. We address these sources uncertainty by implementing three soil moisture (SMRF) and three soil temperature (STRF) respiration functions in an Earth System Model that can be run with three degrees of biogeochemical nutrient limitation (C-only, C and N, and C and N and P). All 27 possible combinations of a SMRF with a STRF and a biogeochemical mode are equilibrated before transient historical (1850–2005) simulations are performed. As expected, implementing N and P limitation reduces the land carbon sink, transforming some regions from net sinks to net sources over the historical period (1850–2005). Differences in the soil C balance implied by the various SMRFs and STRFs also change the sign of some regional sinks. Further, although the absolute uncertainty in global carbon uptake is reduced, the uncertainty due to the SMRFs and STRFs grows relative to the inter-annual variability in net uptake when N and P limitations are added. We also demonstrate that the equilibrated soil C also depend on the shape of the SMRF and STRF. Equilibration using different STRFs and SMRFs and nutrient limitation generates a six-fold range of global soil C that largely mirrors the range in available (17) CMIP5 models. Simulating the historical change in soil carbon therefore critically depends on the choice of STRF, SMRF and nutrient limitation, as it controls the equilibrated state to which transient conditions are applied. This direct effect of the representation of microbial decomposition in Earth System Models adds to recent concerns on the adequacy of these simple representations of very complex soil carbon processes.

Estimates of soil organic carbon stocks in central Canada using three different approaches

2002 ◽  
Vol 32 (5) ◽  
pp. 805-812 ◽  
Author(s):  
J S Bhatti ◽  
M J Apps ◽  
C Tarnocai
Keyword(s):  
Surface Layer ◽  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Soil Carbon ◽  
Soil Depth ◽  
Peat Soil ◽  
Regression Line ◽  
Organic C ◽  
Soil C ◽  
Total Soil

This study compared three estimates of carbon (C) contained both in the surface layer (0–30 cm) and the total soil pools at polygon and regional scales and the spatial distribution in the three prairie provinces of western Canada (Alberta, Saskatchewan, and Manitoba). The soil C estimates were based on data from (i) analysis of pedon data from both the Boreal Forest Transect Case Study (BFTCS) area and from a national-scale soil profile database; (ii) the Canadian Soil Organic Carbon Database (CSOCD), which uses expert estimation based on soil characteristics; and (iii) model simulations with the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS2). At the polygon scale, good agreement was found between the CSOCD and pedon (the first method) total soil carbon values. Slightly higher total soil carbon values obtained from BFTCS averaged pedon data (the first method), as indicated by the slope of the regression line, may be related to micro- and meso-scale geomorphic and microclimate influences that are not accounted for in the CSOCD. Regional estimates of organic C from these three approaches for upland forest soils ranged from 1.4 to 7.7 kg C·m–2 for the surface layer and 6.2 to 27.4 kg C·m–2 for the total soil. In general, the CBM-CFS2 simulated higher soil C content compared with the field observed and CSOCD soil C estimates, but showed similar patterns in the total soil C content for the different regions. The higher soil C content simulated with CBM-CFS2 arises in part because the modelled results include forest floor detritus pool components (such as coarse woody debris, which account for 4–12% of the total soil pool in the region) that are not included in the other estimates. The comparison between the simulated values (the third method) and the values obtained from the two empirical approaches (the first two methods) provided an independent test of CBM-CFS2 soil simulations for upland forests soils. The CSOCD yielded significantly higher C content for peatland soils than for upland soils, ranging from 14.6 to 28 kg C·m–2 for the surface layer and 60 to 181 kg C·m–2 for the total peat soil depth. All three approaches indicated higher soil carbon content in the boreal zone than in other regions (subarctic, grassland).

scholarly journals Effects of litter and root manipulations on soil carbon and nitrogen in a Schrenk’s spruce (Picea schrenkiana) forest

PLoS ONE ◽  
2021 ◽  
Vol 16 (2) ◽  
pp. e0247725
Author(s):  
Haiqiang Zhu ◽  
Lu Gong ◽  
Zhaolong Ding ◽  
Yuefeng Li
Keyword(s):  
Enzyme Activity ◽  
Microbial Biomass ◽  
Organic Carbon ◽  
Soil Carbon ◽  
Abiotic Factors ◽  
Soil C ◽  
Plant Detritus ◽  
Soil C And N ◽  
C And N ◽  
Root Exclusion

Plant detritus represents the major source of soil carbon (C) and nitrogen (N), and changes in its quantity can influence below-ground biogeochemical processes in forests. However, we lack a mechanistic understanding of how above- and belowground detrital inputs affect soil C and N in mountain forests in an arid land. Here, we explored the effects of litter and root manipulations (control (CK), doubled litter input (DL), removal of litter (NL), root exclusion (NR), and a combination of litter removal and root exclusion (NI)) on soil C and N concentrations, enzyme activity and microbial biomass during a 2-year field experiment. We found that DL had no significant effect on soil total organic carbon (SOC) and total nitrogen (TN) but significantly increased soil dissolved organic carbon (DOC), microbial biomass C, N and inorganic N as well as soil cellulase, phosphatase and peroxidase activities. Conversely, NL and NR reduced soil C and N concentrations and enzyme activities. We also found an increase in the biomass of soil bacteria, fungi and actinomycetes in the DL treatment, while NL reduced the biomass of gram-positive bacteria, gram-negative bacteria and fungi by 5.15%, 17.50% and 14.17%, respectively. The NR decreased the biomass of these three taxonomic groups by 8.97%, 22.11% and 21.36%, respectively. Correlation analysis showed that soil biotic factors (enzyme activity and microbial biomass) and abiotic factors (soil moisture content) significantly controlled the change in soil C and N concentrations (P < 0.01). In brief, we found that the short-term input of plant detritus could markedly affect the concentrations and biological characteristics of the C and N fractions in soil. The removal experiment indicated that the contribution of roots to soil nutrients is greater than that of the litter.

scholarly journals Long-term bare fallow experiments offer new opportunities for the quantification and the study of stable carbon in soil

2010 ◽  
Vol 7 (3) ◽  
pp. 4887-4917 ◽  
Author(s):  
P. Barré ◽  
T. Eglin ◽  
B. T. Christensen ◽  
P. Ciais ◽  
S. Houot ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Soil Carbon ◽  
Co2 Concentration ◽  
Soil C ◽  
Climate Conditions ◽  
Stable Pool ◽  
Bare Fallow ◽  
The Stability ◽  
A Site

Abstract. The stability of soil carbon is a major source of uncertainty for the prediction of atmospheric CO2 concentration during the 21st century. Isolating experimentally the stable soil carbon from other, more vulnerable, pools is of prime importance for calibrating soil C models, and gaining insights on the mechanisms leading to soil organic carbon (SOC) stability. Long-term bare fallow experiments, in which the decay of SOC is monitored for decades after inputs from plant material have stopped, represent a unique opportunity to assess the stable organic carbon. We synthesized data from 6 bare fallow experiments of long-duration, covering a range of soil types and climate conditions, at Askov (Denmark), Grignon and Versailles (France), Kursk (Russia), Rothamsted (UK), and Ultuna (Sweden). The conceptual model of SOC being divided into three pools with increasing turnover times, a labile pool (~ years), an intermediate pool (~ decades) and a stable pool (~ several centuries or more) fits well with the long term SOC decays observed in bare fallow soils. The modeled stable pool estimates ranged from 2.7 gC kg−1 at Rothamsted to 6.8 gC kg−1 at Grignon. The uncertainty over the identification of the stable pool is large due to the short length of the fallow records relative to the time scales involved in the decay of soil C. At Versailles, where there is least uncertainty associated with the determination of a stable pool, the soil contains predominantly stable C after 80 years of continuous bare fallow. Such a site represents a unique research platform for future experimentation addressing the characteristics of stable SOC and its vulnerability to global change.

scholarly journals Factors controlling <i>Carex brevicuspis</i> leaf litter decomposition and its contribution to surface soil organic carbon pool at different water levels

2020 ◽  
Author(s):  
Lianlian Zhu ◽  
Zhengmiao Deng ◽  
Yonghong Xie ◽  
Xu Li ◽  
Feng Li ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Soil Carbon ◽  
Water Level ◽  
Leaf Litter ◽  
Litter Decomposition ◽  
Water Levels ◽  
Carbon Pool ◽  
Leaf Litter Decomposition ◽  
Litter Input

Abstract. Litter decomposition plays a vital role in wetland carbon cycling. However, the contribution of aboveground litter decomposition to the wetland soil organic carbon (SOC) pool has not yet been quantified. Here, we conducted a Carex brevicuspis leaf litter input experiment to clarify the intrinsic factors controlling litter decomposition and quantify it's contribution to SOC pool at different water levels. This species is ubiquitous to global freshwater wetlands. We sampled this plant leaf litter at −25, 0, and +25 cm relative to the soil surface over 280 days and analysed leaf litter decomposition and its contribution to the SOC pool. The mass loss and carbon release rates were the highest at +25 cm water level, followed by the 0 cm water level. The rates of these parameters were the lowest at −25 cm water level. Significant amounts of litter carbon, nitrogen, and phosphorus were released at all three water levels. Litter input significantly increased the soil microbial biomass and fungal density but had nonsignificant impacts on soil bacteria, actinomycetes, and fungal/bacterial concentrations at all three water levels. Compared with litter removal, litter application increased the SOC by 25.12 %, 9.58 %, and 4.98 % at the +25 cm, 0 cm, and −25 cm water levels, respectively. Hence, higher water levels facilitate the release of organic carbon from leaf litter into the soil via water leaching. In this way, they strengthen the soil carbon pool. At lower water levels, soil carbon is lost as the slower litter decomposition rate and active microbial (actinomycete) respiration. Our results revealed that the water level in natural wetlands influences litter decomposition mainly by leaching and microbial activity, by extension, affects wetland surface carbon pool.

scholarly journals Dynamics of deep soil carbon – insights from <sup>14</sup>C time-series across a climatic gradient

2018 ◽  
Author(s):  
Tessa Sophia van der Voort ◽  
Utsav Mannu ◽  
Frank Hagedorn ◽  
Cameron McIntyre ◽  
Lorenz Walthert ◽  
...  
Keyword(s):  
Time Series ◽  
Soil Carbon ◽  
Turnover Time ◽  
Climatic Gradient ◽  
Turnover Rates ◽  
Deep Soil ◽  
Dynamic Component ◽  
Soil C ◽  
Terrestrial Carbon Cycle ◽  
Water Extractable Organic Carbon

Abstract. Quantitative constraints on soil organic matter (SOM) dynamics are essential for comprehensive understanding of the terrestrial carbon cycle. Deep soil carbon is of particular interest, as it represents large stocks and its turnover rates remain highly uncertain. In this study, SOM dynamics in both the top and deep soil across a climatic (average temperature ~ 1–9 °C) gradient are determined using time-series (~ 20 years) 14C data from bulk soil and water-extractable organic carbon (WEOC). Analytical measurements reveal enrichment of bomb-derived radiocarbon in the deep soil layers on the bulk level during the last two decades. The WEOC pool is strongly enriched in bomb-derived carbon, indicating that it is a dynamic pool. We used a numerical model to determine turnover time of the bulk, slow and dynamic pool as well as the size of the dynamic pool. The presence of bomb-derived carbon in the deep soil, as well as the rapidly turning over WEOC pool and sizeable dynamic fraction at depth across the climatic gradient implies that there likely is a dynamic component of carbon in the deep soil. Precipitation appears to exert a stronger influence on soil C dynamics than temperature. Overall, geology seems to impact the carbon cycling in three key ways: (1) bedrock-derived (petrogenic) carbon can comprise an important component of the soil carbon pool even at relatively shallow depths (< 1 m). (2) Bedrock type influences water logging either by its porosity or by determining texture, and (3) rock and soil mineralogy controls C stabilization.

scholarly journals Dynamics of deep soil carbon – insights from <sup>14</sup>C time series across a climatic gradient

2019 ◽  
Vol 16 (16) ◽  
pp. 3233-3246 ◽  
Author(s):  
Tessa Sophia van der Voort ◽  
Utsav Mannu ◽  
Frank Hagedorn ◽  
Cameron McIntyre ◽  
Lorenz Walthert ◽  
...  
Keyword(s):  
Time Series ◽  
Soil Carbon ◽  
Turnover Time ◽  
Climatic Gradient ◽  
Deep Soil ◽  
Dynamic Component ◽  
Soil C ◽  
Time Estimates ◽  
Terrestrial Carbon Cycle ◽  
Water Extractable Organic Carbon

Abstract. Quantitative constraints on soil organic matter (SOM) dynamics are essential for comprehensive understanding of the terrestrial carbon cycle. Deep soil carbon is of particular interest as it represents large stocks and its turnover times remain highly uncertain. In this study, SOM dynamics in both the top and deep soil across a climatic (average temperature ∼ 1–9 ∘C) gradient are determined using time-series (∼20 years) 14C data from bulk soil and water-extractable organic carbon (WEOC). Analytical measurements reveal enrichment of bomb-derived radiocarbon in the deep soil layers on the bulk level during the last 2 decades. The WEOC pool is strongly enriched in bomb-derived carbon, indicating that it is a dynamic pool. Turnover time estimates of both the bulk and WEOC pool show that the latter cycles up to a magnitude faster than the former. The presence of bomb-derived carbon in the deep soil, as well as the rapidly turning WEOC pool across the climatic gradient, implies that there likely is a dynamic component of carbon in the deep soil. Precipitation and bedrock type appear to exert a stronger influence on soil C turnover time and stocks as compared to temperature.

Integrating mineral interactions with organic carbon in thawing permafrost to assess climate feedbacks

2020 ◽  
Author(s):  
Sophie Opfergelt ◽  
Catherine Hirst ◽  
Arthur Monhonval ◽  
Elisabeth Mauclet ◽  
Maxime Thomas
Keyword(s):  
Organic Carbon ◽  
Soil Carbon ◽  
Clay Minerals ◽  
Metal Cations ◽  
Mineral Surfaces ◽  
Microbial Decomposition ◽  
Fe Oxides ◽  
Physico Chemical ◽  
Thawing Permafrost ◽  
Chemical Conditions

&lt;p&gt;Permafrost contains 1400-1660 Gt of organic carbon (OC), from which 5-15% will likely be emitted as greenhouse gases (GHG) by 2100. The soil organic carbon stock is distributed between a pool of particulate organic matter (POM), and a pool of mineral-associated OM (MOM). POM can be free, i.e., more readily available for microbial decomposition, or occluded within soil aggregates (involving clay minerals or Fe-Al (hydr)oxides), i.e., spatially inaccessible for microorganisms. MOM includes OC sorbed onto mineral surfaces (such as clay minerals or Fe-oxides) and OC complexed with metal cations (e.g., Al, Fe, Ca), i.e., stabilized OC. The interactions between OC and minerals influence the accessibility of OC for microbial decomposition and OC stability and are therefore a factor in controlling the C emissions rate upon thawing permafrost.&lt;/p&gt;&lt;p&gt;In the warming Arctic, there is growing evidence for soil disturbance such as coastal erosion, thermokarst and soil drainage as a consequence of abrupt and gradual permafrost thaw. These disturbances induce changes in the physico-chemical conditions controlling mineral solubility in permafrost soils which directly affect the stability of the MOM and of the occluded POM. As a consequence, a portion of OC can be unlocked and transferred into the free POM. This additional pool of freely available OC may be degraded and amplify C emissions from permafrost to the atmosphere. Conversely, the concomitant release of metal cations upon permafrost thaw may partly mitigate permafrost C emissions by stabilization of OC via complexation or sorption onto mineral surfaces and return a portion of freely available OC to the MOM. The majority of C is emitted as CO&lt;sub&gt;2&lt;/sub&gt; but 1.5 and 3.5% of the total permafrost C emissions will be released as CH&lt;sub&gt;4&lt;/sub&gt;, with implications for the atmospheric radiative forcing balance. Importantly, the proportion CH&lt;sub&gt;4&lt;/sub&gt; emitted relative to CO&lt;sub&gt;2&lt;/sub&gt; is likely to increase with increasing abrupt thaw and associated anoxic conditions, but a portion of CH&lt;sub&gt;4&lt;/sub&gt; emissions could be mitigated by the anoxic oxidation of methane mediated by the presence of Fe-oxides exposed by abrupt thaw of deep permafrost.&lt;/p&gt;&lt;p&gt;This contribution aims at assessing how changing soil physico-chemical conditions affect interactions between mineral surfaces and OC in thawing permafrost. Scenarios of mineral-organic interactions during gradual thaw, including changes in water drainage and talik formation, and abrupt thaw including shifting redox conditions associated with thermokarst will be presented. Approaches to quantify changes in mineral-organic interactions will be discussed. By integrating the most recent studies from the permafrost carbon community with soil mineralogy, soil chemistry and soil hydrology, this contribution demonstrates that the fate of mineral-organic interactions upon thawing must be considered given their potential implications for GHG emissions. If we do not include the role of mineral-organic interactions in this puzzle, the complexities involved in soil carbon decomposition may propagate large uncertainties into coupled soil carbon-climate feedback predictions.&lt;/p&gt;

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