A theoretical analysis of steady state δ13C profiles of soil organic matter

2004 ◽  
Vol 18 (2) ◽  
pp. n/a-n/a ◽  
Author(s):  
Michael A. Poage ◽  
Xiahong Feng
Keyword(s):  
Organic Matter ◽  
Steady State ◽  
Soil Organic Matter ◽  
Theoretical Analysis

scholarly journals Colimitation of decomposition by substrate and decomposers – a comparison of model formulations

2008 ◽  
Vol 5 (1) ◽  
pp. 163-190 ◽  
Author(s):  
T. Wutzler ◽  
M. Reichstein
Keyword(s):  
Organic Matter ◽  
Steady State ◽  
Soil Organic Matter ◽  
Priming Effect ◽  
Deep Soil ◽  
Fresh Organic Matter ◽  
Decomposition Models ◽  
Decomposer Community ◽  
Som Decomposition

Abstract. Decomposition of soil organic matter (SOM) is limited by both the available substrate and the active decomposer community. The understanding of this colimitation strongly affects the understanding of feedbacks of soil carbon to global warming and its consequences. This study compares different formulations of soil organic matter (SOM) decomposition. We compiled formulations from literature into groups according to the representation of decomposer biomass on the SOM decomposition rate a) non-explicit (substrate only), b) linear, and c) non-linear. By varying the SOM decomposition equation in a basic simplified decomposition model, we analyzed the following questions. Is the priming effect represented? Under which conditions is SOM accumulation limited? And, how does steady state SOM stocks scale with amount of fresh organic matter (FOM) litter inputs? While formulations (a) did not represent the priming effect, with formulations (b) steady state SOM stocks were independent of amount of litter input. Further, with several formulations (c) there was an offset of SOM that was not decomposed when no fresh OM was supplied. The finding that a part of the SOM is not decomposed on exhaust of FOM supply supports the hypothesis of carbon stabilization in deep soil by the absence of energy-rich fresh organic matter. Different representations of colimitation of decomposition by substrate and decomposers in SOM decomposition models resulted in qualitatively different long-term behaviour. A collaborative effort by modellers and experimentalists is required to identify appropriate and inappropriate formulations.

scholarly journals Long-term steady state <sup>13</sup>C labelling to investigate soil carbon turnover in grasslands

2007 ◽  
Vol 4 (3) ◽  
pp. 385-394 ◽  
Author(s):  
K. Klumpp ◽  
J. F. Soussana ◽  
R. Falcimagne
Keyword(s):  
Organic Matter ◽  
Steady State ◽  
Soil Organic Matter ◽  
Soil Carbon ◽  
Residence Time ◽  
Particulate Organic Matter ◽  
Mean Residence Time ◽  
Carbon Turnover ◽  
13C Labelling

Abstract. We have set up a facility allowing steady state 13CO2 labeling of short stature vegetation (12 m2) for several years. 13C labelling is obtained by scrubbing the CO2 from outdoors air with a self-regenerating molecular sieve and by replacing it with 13C depleted (−34.7±0.03‰) fossil-fuel derived CO2 The facility, which comprises 16 replicate mesocosms, allows to trace the fate of photosynthetic carbon in plant-soil systems in natural light and at outdoors temperature. This method was applied to the study of soil organic carbon turnover in temperate grasslands. We tested the hypothesis that a low disturbance by grazing and cutting of the grassland increases the mean residence time of carbon in coarse (>0.2 mm) soil organic fractions. Grassland monoliths (0.5×0.5×0.4 m) were sampled from high and low disturbance treatments in a long-term (14 yrs) grazing experiment and were placed during two years in the mesocosms. During daytime, the canopy enclosure in each mesocosm was supplied in an open flow with air at mean CO2 concentration of 425 µmol mol−1 and δ13C of −21.5±0.27‰. Fully labelled mature grass leaves reached a δ13C of −40.8 (±0.93) and −42.2‰ (±0.60) in the low and high disturbance treatments, respectively, indicating a mean 13C labelling intensity of 12.7‰ compared to unlabelled control grass leaves. After two years, the delta 13C value of total soil organic matter above 0.2 mm was reduced in average by 7.8‰ in the labelled monoliths compared to controls. The isotope mass balance technique was used to calculate for the top (0–10 cm) soil the fraction of 13C labelled carbon in the soil organic matter above 0.2 mm (i.e. roots, rhizomes and particulate organic matter). A first order exponential decay model fitted to the unlabelled C in this fraction shows an increase in mean residence time from 22 to 31 months at low compared to high disturbance. A slower decay of roots, rhizomes and particulate organic matter above 0.2 mm is therefore likely to contribute to the observed increased in soil carbon sequestration in grassland monoliths exposed to low disturbance.

An analysis of soil organic matter dynamics in relation to management, erosion and yield of wheat in long-term crop rotation plots

1997 ◽  
Vol 77 (4) ◽  
pp. 553-563 ◽  
Author(s):  
C. M. Monreal ◽  
R. P. Zentner ◽  
J. A. Robertson
Keyword(s):  
Organic Matter ◽  
Steady State ◽  
Soil Organic Matter ◽  
Soil Erosion ◽  
Grain Yield ◽  
State Level ◽  
Organic N ◽  
Steady State Level ◽  
Wheat Grain

We examined the influence of management on soil organic matter (SOM) dynamics and yield of wheat grain in semiarid Chernozemic and humid Gray Luvisolic soils. The Century model was tested with data obtained from long-term research plots cropped to wheat (Triticum aestivum L.) monoculture and cereal-hay (CH). Century simulated changes in soil organic-C (OC) and organic-N (ON) within 10% of actual measurements taken over decades. Our analysis indicated that management and soil erosion affected the time required for SOM to achieve new steady-state level (Tst). Tst ranged between 12 yr under wheat and 46 yr under CH cropping. Increasing the SOM content of degraded soils to new steady-state level appears to increase grain yield between 86 kg ha−1 and 840 kg ha−1.Wheat-fallow (WF) rotation plots receiving <10 kg N ha−1 yr−1, and with erosion >13.6 t ha−1 yr−1 degraded SOM. The average long-term yield of wheat grain (including new high yielding varieties) was maintained at <910 kg ha−1 yr−1 under degraded SOM content. Well-fertilized continuous wheat (CW) and CH rotation plots with erosion <4 t ha−1 yr−1 aggraded SOM content, and maintained the long-term average grain yield at >1290 kg ha−1 yr−1. Sustained OC levels were attained by returning 1030 kg C ha−1 yr−1 as plant residue (roots + aboveground) and keeping soil erosion ≤12.8 t ha−1 yr−1. Sustainable crop production systems need to consider SOM dynamics and erosion as factors limiting grain yield even after introducing genetically improved wheat varieties. Key words: Management, organic matter, erosion, dynamics, yield, manure, nitrogen, tillage, steady-state

scholarly journals Colimitation of decomposition by substrate and decomposers – a comparison of model formulations

2008 ◽  
Vol 5 (3) ◽  
pp. 749-759 ◽  
Author(s):  
T. Wutzler ◽  
M. Reichstein
Keyword(s):  
Organic Matter ◽  
Steady State ◽  
Soil Organic Matter ◽  
Priming Effect ◽  
Deep Soil ◽  
Fresh Organic Matter ◽  
Decomposition Models ◽  
Decomposer Community ◽  
Som Decomposition

Abstract. Decomposition of soil organic matter (SOM) is limited by both the available substrate and the active decomposer community. The understanding of this colimitation strongly affects the understanding of feedbacks of soil carbon to global warming and its consequences. This study compares different formulations of soil organic matter (SOM) decomposition. We compiled formulations from literature into groups according to the representation of decomposer biomass on the SOM decomposition rate a) non-explicit (substrate only), b) linear, and c) non-linear. By varying the SOM decomposition equation in a basic simplified decomposition model, we analyzed the following questions. Is the priming effect represented? Under which conditions is SOM accumulation limited? And, how does steady state SOM stocks scale with amount of fresh organic matter (FOM) litter inputs? While formulations (a) did not represent the priming effect, with formulations (b) steady state SOM stocks were independent of amount of litter input. Further, with several formulations (c) there was an offset of SOM that was not decomposed when no fresh OM was supplied. The finding that a part of the SOM is not decomposed on exhaust of FOM supply supports the hypothesis of carbon stabilization in deep soil by the absence of energy-rich fresh organic matter. Different representations of colimitation of decomposition by substrate and decomposers in SOM decomposition models resulted in qualitatively different long-term behaviour. A collaborative effort by modellers and experimentalists is required to identify formulations that are more or less suitable to represent the most important drivers of long term carbon storage.

scholarly journals DRIFTS band areas as measured pool size proxy to reduce parameter uncertainty in soil organic matter models

2020 ◽  
Vol 17 (6) ◽  
pp. 1393-1413 ◽  
Author(s):  
Moritz Laub ◽  
Michael Scott Demyan ◽  
Yvonne Funkuin Nkwain ◽  
Sergey Blagodatsky ◽  
Thomas Kätterer ◽  
...  
Keyword(s):  
Organic Matter ◽  
Steady State ◽  
Soil Organic Matter ◽  
Absorption Band ◽  
Parameter Uncertainty ◽  
Turnover Rates ◽  
Bayesian Calibration ◽  
Individual Site ◽  
Bare Fallow

Abstract. Soil organic matter (SOM) turnover models predict changes in SOM due to management and environmental factors. Their initialization remains challenging as partitioning of SOM into different hypothetical pools is intrinsically linked to model assumptions. Diffuse reflectance mid-infrared Fourier transform spectroscopy (DRIFTS) provides information on SOM quality and could yield a measurable pool-partitioning proxy for SOM. This study tested DRIFTS-derived SOM pool partitioning using the Daisy model. The DRIFTS stability index (DSI) of bulk soil samples was defined as the ratio of the area below the aliphatic absorption band (2930 cm−1) to the area below the aromatic–carboxylate absorption band (1620 cm−1). For pool partitioning, the DSI (2930 cm−1 ∕ 1620 cm−1) was set equal to the ratio of fast-cycling ∕ slow-cycling SOM. Performance was tested by simulating long-term bare fallow plots from the Bad Lauchstädt extreme farmyard manure experiment in Germany (Chernozem, 25 years), the Ultuna continuous soil organic matter field experiment in Sweden (Cambisol, 50 years), and 7 year duration bare fallow plots from the Kraichgau and Swabian Jura regions in southwest Germany (Luvisols). All experiments were at sites that were agricultural fields for centuries before fallow establishment, so classical theory would suggest that a steady state can be assumed for initializing SOM pools. Hence, steady-state and DSI initializations were compared, using two published parameter sets that differed in turnover rates and humification efficiency. Initialization using the DSI significantly reduced Daisy model error for total soil organic carbon and microbial carbon in cases where assuming a steady state had poor model performance. This was irrespective of the parameter set, but faster turnover performed better for all sites except for Bad Lauchstädt. These results suggest that soils, although under long-term agricultural use, were not necessarily at a steady state. In a next step, Bayesian-calibration-inferred best-fitting turnover rates for Daisy using the DSI were evaluated for each individual site or for all sites combined. Two approaches significantly reduced parameter uncertainty and equifinality in Bayesian calibrations: (1) adding physicochemical meaning with the DSI (for humification efficiency and slow SOM turnover) and (2) combining all sites (for all parameters). Individual-site-derived turnover rates were strongly site specific. The Bayesian calibration combining all sites suggested a potential for rapid SOM loss with 95 % credibility intervals for the slow SOM pools' half-life being 278 to 1095 years (highest probability density at 426 years). The credibility intervals of this study were consistent with several recently published Bayesian calibrations of similar two-pool SOM models, i.e., with turnover rates being faster than earlier model calibrations suggested; hence they likely underestimated potential SOM losses.

scholarly journals DRIFTS peaks as measured pool size proxy to reduce parameter uncertainty of soil organic matter models

2019 ◽  
Author(s):  
Moritz Laub ◽  
Michael Scott Demyan ◽  
Yvonne Funkuin Nkwain ◽  
Sergey Blagodatsky ◽  
Thomas Kätterer ◽  
...  
Keyword(s):  
Organic Matter ◽  
Steady State ◽  
Soil Organic Matter ◽  
Parameter Uncertainty ◽  
Stability Index ◽  
Turnover Rates ◽  
Bayesian Calibration ◽  
Agricultural Use ◽  
Bare Fallow

Abstract. The initialization of soil organic matter (SOM) turnover models has been a challenge for decades. Instead of using laborious and error prone size-density fractionation SOM pool partitioning, we propose the inexpensive, rapid, and non destructive Diffuse reflectance mid infrared Fourier transform spectroscopy (DRIFTS) technique on bulk soil samples to gain information on SOM pool partitioning from the spectra. Specifically, the DRIFTS stability index, defined as the ratio of aliphatic C-H (2930 cm−1) to aromatic C=C (1620 cm−1) stretching vibrations, was used to divide SOM into fast and slow cycling pools in the soil organic module of the DAISY model. Long-term bare fallow plots from Bad Lauchstädt (Chernozem, 25 years) and the Ultuna frame trial in Sweden (Cambisol, 50 years) were combined with bare fallow plots of 7 years duration in the Kraichgau and Swabian Jura region in Southwest Germany (Luvisols). All fields had been in agricultural use for centuries before fallow establishment, so classical theory would suggest an initial steady state of SOM, which was hence used to compare the performance of DAISY initializations against the newly established DRIFTS stability index. The test was done using two different published parameter sets (2.7 × 10−6 d−1, 1.4 × 10−4 d−1, 0.1 compared to 4.3 × 10−5 d−1, 1.4 × 10−4 d−1, 0.3 for the turnover rates of slow pool, fast pool and humification efficiency, respectively). The DRIFTS initialization of SOM pools significantly reduced model errors of poor performing model runs assuming steady state, irrespective of the turnover rates used, but the faster turnover parameter set fit better to all sites except Bad Lauchstädt. This suggests that soils under long-term agricultural use were not necessarily at steady state. A Bayesian calibration was applied in a next step to identify the best-fitting turnover rates for the DRIFTS stability index in DAISY, both for each site individually and for a combination of all sites. The two approaches which significantly reduced parameter uncertainty and equifinality were: (1) the addition of the physico-chemically based DRIFTS stability index, and (2) combining several sites into one Bayesian calibration, as derived turnover rates can be strongly site specific. The combination of all four sites showed that SOM is likely lost at relatively fast turnover rates with the 95 % credibility intervals of the slow SOM pools half life ranging from 278 to 1095 years, with 426 years as a value of highest probability density. The credibility intervals of this study were consistent with several recently published Bayesian calibrations of similar SOM models, all turnover rates were considerably faster than earlier models suggested. It is therefore likely that published turnover rates understimate the potential loss of SOM.

scholarly journals A global model of carbon, nitrogen and phosphorus cycles for the terrestrial biosphere

2010 ◽  
Vol 7 (7) ◽  
pp. 2261-2282 ◽  
Author(s):  
Y. P. Wang ◽  
R. M. Law ◽  
B. Pak
Keyword(s):  
Organic Matter ◽  
Steady State ◽  
Soil Organic Matter ◽  
Primary Productivity ◽  
Net Primary Productivity ◽  
Terrestrial Ecosystems ◽  
Plant Litter ◽  
Terrestrial Biosphere ◽  
P Limitation ◽  
P Mineralization

Abstract. Carbon storage by many terrestrial ecosystems can be limited by nutrients, predominantly nitrogen (N) and phosphorus (P), in addition to other environmental constraints, water, light and temperature. However the spatial distribution and the extent of both N and P limitation at the global scale have not been quantified. Here we have developed a global model of carbon (C), nitrogen (N) and phosphorus (P) cycles for the terrestrial biosphere. Model estimates of steady state C and N pool sizes and major fluxes between plant, litter and soil pools, under present climate conditions, agree well with various independent estimates. The total amount of C in the terrestrial biosphere is 2767 Gt C, and the C fractions in plant, litter and soil organic matter are 19%, 4% and 77%. The total amount of N is 135 Gt N, with about 94% stored in the soil, 5% in the plant live biomass, and 1% in litter. We found that the estimates of total soil P and its partitioning into different pools in soil are quite sensitive to biochemical P mineralization. The total amount of P (plant biomass, litter and soil) excluding occluded P in soil is 17 Gt P in the terrestrial biosphere, 33% of which is stored in the soil organic matter if biochemical P mineralization is modelled, or 31 Gt P with 67% in soil organic matter otherwise. This model was used to derive the global distribution and uncertainty of N or P limitation on the productivity of terrestrial ecosystems at steady state under present conditions. Our model estimates that the net primary productivity of most tropical evergreen broadleaf forests and tropical savannahs is reduced by about 20% on average by P limitation, and most of the remaining biomes are N limited; N limitation is strongest in high latitude deciduous needle leaf forests, and reduces its net primary productivity by up to 40% under present conditions.

scholarly journals Radiocarbon Dating of Soil Organic Matter

1996 ◽  
Vol 45 (3) ◽  
pp. 282-288 ◽  
Author(s):  
Yang Wang ◽  
Ronald Amundson ◽  
Susan Trumbore
Keyword(s):  
Organic Matter ◽  
Steady State ◽  
Soil Organic Matter ◽  
Radiocarbon Dating ◽  
Soil Depth ◽  
Soil Formation ◽  
Soil Horizon ◽  
Buried Soils ◽  
Model Calculations ◽  
Soil C

AbstractRadiocarbon ages of soil organic matter are evaluated with a model which incorporates the dynamics of the 14C content of soil organic matter. Measured 14C ages of soil organic matter or its fractions are always younger than the true ages of soils due to continuous input of organic matter into soils. Differences in soil C dynamics due to climate or soil depth will result in significantly different 14C signatures of soil organic matter for soils of the same age. As a result, the deviation of the measured 14C age from the true age of soil formation could differ significantly among different soils or soil horizons. Our model calculations also suggest that 14C ages of soil organic matter will eventually reach a steady state provided that no climatic or ecological perturbations occur. Once a soil or a soil horizon has reached a steady state, 14C dating of soil organic matter will provide no useful information regarding the age of the soil. However, for soils in which steady state has not been reached, it is possible to estimate the age of soil formation by modeling the measured 14C contents of soil organic matter. Radiocarbon dating of buried soils could, in general, overestimate the true age of the burial by as much as the steady-state age of the soil or soil horizon.

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