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 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

The long-term effect of biochar on composition of soil organic matter 

2021 ◽  
Author(s):  
Sandra Pärnpuu ◽  
Karin Kauer ◽  
Henn Raave
Keyword(s):  
Organic Matter ◽  
Nmr Spectroscopy ◽  
Soil Organic Matter ◽  
Soil Samples ◽  
Bulk Soil ◽  
Organic C ◽  
Native Soil ◽  
Soil Hydrophobicity ◽  
Som Decomposition

&lt;p&gt;Biochar has been described as relatively stable form of C with long mean residence time due to its predominantly aromatic structure. Addition of biochar can sequester C in the soil, albeit the effect of biochar on native soil organic C decomposition, whether it stimulates or reduces the decomposition of native soil organic matter, requires further understanding. The aim of this research was to study the long-term impact of biochar (BC) on the composition of soil organic matter (SOM) in Fragi-Stagnic Albeluvisol. The work was compiled on the basis of field experiment, set up on a production field in 2011. The experiment was drawn up of two treatments and four replicates, where on half of the replicates slow-pyrolysis hardwood BC (51.8% C, 0.43% N) produced at 500-600 &amp;#176;C was applied 50 Mg ha&lt;sup&gt;-1&lt;/sup&gt;. The soil samples were collected from 0-10 cm soil layer in autumn 2020. The air-dried samples were sieved through a 2-mm sieve and divided into two fractions: the particulate organic matter (POM) fraction (soil particles larger than 0.063 mm) and the mineral-associated organic matter (MAOM) (&lt;0.063 mm) by density fractionation method. The soil organic carbon (SOC) and total nitrogen (Ntot) concentrations of bulk soil and fractions were measured. The chemical composition of SOM was studied using &lt;sup&gt;13&lt;/sup&gt;C nuclear magnetic resonance (NMR) spectroscopy. Bulk soil samples and fractions were pretreated with 10% HF solution before NMR spectroscopy analysis. Two indices were calculated: the ratio of alkyl C/O-alkyl C, which describes the degree of SOM decomposition and soil hydrophobicity (HI): (aromatic-C+alkyl-C)/O/N-Alkyl-C.&lt;/p&gt;&lt;p&gt;The addition of BC to the soil increased the SOC concentration but did not influence the Ntot concentration and the soil C/N ratio increased from 11.6 to 16.7. The distribution of POM and MAOM was not affected by the BC and POM proportion accounted for an average of 57&amp;#8211;58%. The SOC concentrations of POM and MAOM fractions were higher in the BC variant. The BC increased the proportion of aromatic-C in the SOM, as the proportion of aromatic-C in initial BC was high (almost 92%). Initially the BC is inherently highly hydrophobic and increased the HI of bulk soil, POM, and MAOM fractions. The HI increased in line: MAOM&lt;bulk&lt;POM (1.51&lt;1.67&lt;1.97). An increase in HI inhibits the decomposition of SOM and it was also confirmed by a decreased ratio of alkyl-C/O-alkyl-C after the BC addition. The decomposition degree was lowest in POM fraction where SOC concentration was more than doubled due to BC. The suppressed decomposition was caused by the limitation of soil Ntot concentration and increased C/N ratio.&lt;/p&gt;&lt;p&gt;In conclusion, the effect of BC on the composition of SOM was still evident after 10 years of increasing SOC concentration and soil hydrophobicity and decreasing SOM decomposition degree promoting C sequestration to the soil.&lt;/p&gt;&lt;p&gt;This work was supported by the Estonian Research Council grant PSG147.&lt;/p&gt;

scholarly journals Measuring and modelling continuous quality distributions of soil organic matter

2009 ◽  
Vol 6 (5) ◽  
pp. 9045-9082 ◽  
Author(s):  
S. Bruun ◽  
G. I. Ågren ◽  
B. T. Christensen ◽  
L. S. Jensen
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Management Practices ◽  
Model Development ◽  
Turnover Rates ◽  
Continuous Distributions ◽  
Continuous Quality ◽  
Direct Interpretation ◽  
Decomposition Models ◽  
Som Decomposition

Abstract. An understanding of the dynamics of soil organic matter (SOM) is important for our ability to develop management practices that preserve soil quality and sequester carbon. Most SOM decomposition models represent the heterogeneity of organic matter by a few discrete compartments with different turnover rates, while other models employ a continuous quality distribution. To make the multi-compartment models more mechanistic in nature, it has been argued that the compartments should be related to soil fractions actually occurring and having a functional role in the soil. In this paper, we make the case that fractionation methods that can measure continuous quality distributions should be developed, and that the temporal development of these distributions should be incorporated into SOM models. The measured continuous SOM quality distributions should hold valuable information not only for model development, but also for direct interpretation. Measuring continuous distributions requires that the measurements along the quality variable are so frequent that the distribution is approaching the underlying continuum. Continuous distributions leads to possible simplifications of the model formulations, which considerably reduce the number of parameters needed to describe SOM turnover. A general framework for SOM models representing SOM across measurable quality distributions is presented and simplifications for specific situations are discussed. Finally, methods that have been used or have the potential to be used to measure continuous quality SOM distributions are reviewed. Generally, existing fractionation methods have to be modified to allow measurement of distributions or new fractionation techniques will have to be developed. Developing the distributional models in concert with the fractionation methods to measure the distributions will be a major task. We hope the current paper will help spawning the interest needed to accommodate this.

scholarly journals Long-Term Bare Fallow Soil Reveals The Temperature Sensitivity of Priming Effect of The Relatively Stabilized Soil Organic Matter

2021 ◽  
Author(s):  
Xiuwei Zhang ◽  
Biao Zhu ◽  
Feihai Yu ◽  
Peng Wang ◽  
Weixin Cheng
Keyword(s):  
Organic Matter ◽  
Priming Effect ◽  
Field Soil ◽  
Old Field ◽  
Maize Leaves ◽  
Fallow Soil ◽  
Bare Fallow ◽  
Som Decomposition ◽  
Microbial N

Abstract Priming plays an important role in modifying the decomposition of soil organic matter (SOM), but there are large uncertainties in the temperature effect on priming mainly due to the variation in SOM stability. Long-term bare fallow offers a unique opportunity to isolate the relatively stabilized SOM pool and study its properties. We tested the temperature effect on priming of the relatively stabilized SOM pool by incubating soil samples collected from a bare fallow (representing the relatively stabilized SOM) and its adjacent old field (containing both stabilized SOM and labile SOM) at 10 and 20°C for 815 days. We amended the soil samples with C4 maize leaves to distinguish the CO2 source released from the soils (formed under C3 vegetation) and the substrate added (i.e. maize leaves) based on the natural abundance of δ13C. In all cases, there was a positive priming effect on native SOM decomposition when fresh organic matter (maize leaves) was added. The temperature sensitivity of priming effect (calculated as the difference in SOM decomposition due to the addition of maize leaves) in the bare fallow soil and the old field soil was quite different: increasing temperature significantly enhanced the magnitude of priming effect in the bare fallow soil, whereas had no effect on the magnitude of priming effect in the old field soil. The increase of the amount of microbial biomass C by maize leaves application was higher in the bare fallow soil than in the old field soil. Furthermore, for maize leaves-treated soil, temperature increase significantly increased the rate of microbial N mining throughout the incubation in the bare fallow soil, but had minor effect on microbial N mining in the old field soil at the end of incubation. We conclude that the priming effect of the relatively stabilized SOM was sensitive to temperature increase, which may be mainly driven by greater microbial growth and microbial demand for N. This work highlights the vulnerability of stabilized SOM to priming effect under global warming and reveals the potential role of microbes in regulating soil C dynamics under future climate change.

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 Measuring and modeling continuous quality distributions of soil organic matter

2010 ◽  
Vol 7 (1) ◽  
pp. 27-41 ◽  
Author(s):  
S. Bruun ◽  
G. I. Ågren ◽  
B. T. Christensen ◽  
L. S. Jensen
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Management Practices ◽  
Model Development ◽  
Turnover Rates ◽  
Continuous Distributions ◽  
Continuous Quality ◽  
Direct Interpretation ◽  
Decomposition Models ◽  
Som Decomposition

Abstract. An understanding of the dynamics of soil organic matter (SOM) is important for our ability to develop management practices that preserve soil quality and sequester carbon. Most SOM decomposition models represent the heterogeneity of organic matter by a few discrete compartments with different turnover rates, while other models employ a continuous quality distribution. To make the multi-compartment models more mechanistic in nature, it has been argued that the compartments should be related to soil fractions actually occurring and having a functional role in the soil. In this paper, we make the case that fractionation methods that can measure continuous quality distributions should be developed, and that the temporal development of these distributions should be incorporated into SOM models. The measured continuous SOM quality distributions should hold valuable information not only for model development, but also for direct interpretation. Measuring continuous distributions requires that the measurements along the quality variable are so frequent that the distribution approaches the underlying continuum. Continuous distributions lead to possible simplifications of the model formulations, which considerably reduce the number of parameters needed to describe SOM turnover. A general framework for SOM models representing SOM across measurable quality distributions is presented and simplifications for specific situations are discussed. Finally, methods that have been used or have the potential to be used to measure continuous quality SOM distributions are reviewed. Generally, existing fractionation methods will have to be modified to allow measurement of distributions or new fractionation techniques will have to be developed. Developing the distributional models in concert with the fractionation methods to measure the distributions will be a major task. We hope the current paper will help generate the interest needed to accommodate this.

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