Source: CORNELL UNIVERSITY submitted to
SOIL ORGANIC CARBON INTERACTIONS WITH ORGANIC MATTER ADDITIONS: MECHANISMS AND MODELS
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
AFRI COMPETITIVE GRANT
Reporting Frequency
Annual
Accession No.
1003449
Grant No.
2014-67003-22069
Cumulative Award Amt.
$620,000.00
Proposal No.
2014-04488
Multistate No.
(N/A)
Project Start Date
Aug 1, 2014
Project End Date
Jul 31, 2018
Grant Year
2014
Program Code
[A3161]- Interagency Climate Change NASA
Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853
Performing Department
Crop and Soil Sciences
Non Technical Summary
There is a great need to accurately quantify the effects of climate change on soil organic carbon and to evaluate strategies for mitigating global warming. Since organic carbon in soils greatly exceeds the atmospheric contents of carbon dioxide, small changes in soil organic carbon have large effects on the climate. One mechanism which has not been included in models to predict soil carbon dynamics and therefore climate, is the influence that added pyrogenic carbon has on the mineralization of existing organic carbon in soil. This has relevance to regions that experience a greater prevalence of vegetation fires, to soil that already contain large amounts of pyrogenic carbon and to the intentional addition of pyrogenic carbon for soil carbon sequestration.This project will develop the fundamental understanding of how different pyrogenic carbon forms affect the soil carbon cycles, quantify the direction and magnitude of these effects and develop the modeling platform to insert the insights into existing prediction models for soil carbon and global climate. The experiments will employ techniques to separately quantify the different soil carbon fluxes and investigate the location of any remaining carbon on mineral surfaces.The model component developed by this project will enable more accurate predictions of future changes in soil carbon, which is important not only for climate change simulations, but also to decide on the most appropriate mitigation strategies for both global warming as well as soil degradation.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1020110106060%
1020430107040%
Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships;

Subject Of Investigation
0110 - Soil; 0430 - Climate;

Field Of Science
1060 - Biology (whole systems); 1070 - Ecology;
Keywords
Goals / Objectives
The main goal of the proposed project is the improvement of earth system models (with a particular focus on the Community Land Model; CLM) by quantifying and improving our mechanistic understanding of the impact of priming by organic matter, pyC, and root exudates on SOC stocks in both mineral soils and also in vulnerable C stocks of forest organic horizons. This goal will be reached by addressing three specific objectives:Objective 1. To quantify priming effects of organic substrates of varying quality on npSOC, and how these priming effects vary with soil, substrate and environmental parameters over time, giving particular regard to key parameters required to incorporate results into existing SOC models.Objective 2. To determine which mechanisms dominate SOC priming interactions with a range of pyC materials in natural soils, across a broad range of globally-applicable environmental conditions and nutrient statuses, both with and without live plants present, using targeted laboratory and growth-chamber studies.Objective 3. To apply the findings from Objectives 1 and 2 to two key soil carbon cycle models (CENTURY and CLM-CN, the carbon-nitrogen cycling module of the CESM's Community Land Model) to include the effect of priming on SOC cycling dynamics, which may mean modifying rate constants, partitioning constants, or C pools, depending on which mechanisms are found to drive these interactions.
Project Methods
Objective 1:To assess how the priming effect may vary under different conditions, a broad array of incubation experiments will be carried out on mineral soils and forest organic horizons, with varying qualities of organic matter addition, soil texture, soil nutrient status and temperature. These parameters represent the key parameters required to incorporate results into existing SOC models including CLM-CN and other major soil C cycle models, including CENTURY.Labeled pyC production: Biomass of three plant types will be studied, one grassy (Schizachyrium scoparium) and two woody (Salix hybrid 'SV1', and Cupressus x leylandii), which will be grown in growth chambers in an elevated 13CO2 atmosphere in order to achieve a strong, continuous, isotopic label of the pyC. Thus, biomass will be more enriched in 13C relative to the soil than would be possible by use of natural-abundance variation such as a C4 plant in a C3 soil.It has been common practice in most previous studies of pyC priming for pyC properties to be varied only by altering the feedstock and pyrolysis conditions. An important drawback of this approach is that it leads to pyC samples that differ in multiple ways, making it difficult to draw robust conclusions about which properties give rise to which observed effects. We shall, therefore, employ an approach in which biomass samples will be pyrolysed under highly-controlled conditions, followed by post-treatments designed to alter the pyC samples in well-defined ways. The first post-treatment will be removal of labile organic compounds (tars and volatiles) from the pyC by acetone extraction. The second post-treatment is 2M HCl extraction to remove ash and basic cations, followed by washing in deionized water and evaporation to dryness.As with pyC, the mineral soil samples will be altered by the use of controlled treatments. The two treatments to be applied to the mineral soils (in addition to an unamended controls) are: (1) addition of nutrient solution; and/or (2) a 4-month pre-incubation at 30°C and 55% water-holding capacity to remove readily-decomposable organic matter content.Objective 2:Mechanism identification: In addition to simply quantifying the priming effect, the CO­2 efflux and MB measurements will also be critical for Objective 2 (understanding which mechanisms underlie the observed priming). Different mechanisms will have distinct effects on the timing and duration of priming effects, on the relative changes in pyC or npSOC respired, and on the impact of different treatments on the priming effect. Preliminary incubation experiments undertaken in the PI's lab have already shown the presence of distinct signatures in the size, sign, time of onset, and duration of priming effects, which vary with substrate properties. These distinct signatures can aid in determining the underlying mechanisms because different mechanisms would be expected to manifest in different ways. For example, co-metabolism would manifest as an increase in MB correlated with both labile-pyC respiration and with positive priming. Preferential substrate utilization, on the other hand, would also result in an increased MB associated with labile-pyC respiration, but would be differentiated from co-metabolism due to its causing negative priming, and because it would persist only until microbial biomass had grown to accommodate the availability of an additional substrate. Stimulation due to alleviation of nutrient constraints by the nutrient content of pyC would be seen as positive priming that correlates positively with the nutrient content of the pyC and negatively with the addition of nutrients to the soil. Microbial inhibition would cause negative priming and simultaneous reduction in MB that is correlated with the addition of the pyC fraction (acetone-extractable, HCl-extractable, or recalcitrant components) that causes the inhibition. The dilution effect, if it occurs, would only be expected do so briefly during the first hours of incubation until microbial populations begin to adjust to the presence of the new substrate. As such, it is unlikely to be easily apparent without close monitoring of respiration rates during the very early stages. Apparent priming due to increased or decreased microbial biomass turnover, on the other hand, may be measurable if it persists long enough to have a significant impact on overall SOC cycling, and would be quantifiable by the change in microbial biomass.Both adsorption and stabilization of npSOC on pyC would be expected to manifest as negative priming which is associated with the stable fraction of pyC, but not with the labile or ash fractions. However, this negative priming effect can be obscured by simultaneous positive priming during the early stages of incubation, and net negative priming may not become apparent until several months or more than a year has passed, and would not necessarily all be attributable to stabilization. Stabilization would also be evident in an increase in organo-mineral micro-aggregates discernible by soil fractionation. However, soil fractionation may not distinguish between stable-pyC/mineral, labile-pyC/mineral, npSOC/mineral or npSOC/pyC/mineral assemblages. Because of these methodological difficulties in determining whether npSOC is being adsorbed or stabilized on pyC surfaces from macroscopic observations alone, it is proposed to use a complementary paired-combination of nanoSIMS and high spatial-resolution mass spectrometry (LA-AMS) to directly observe the distribution and composition of organic substances on pyC surfaces, their isotopic signatures to determine their source, and also their associations with minerals and microbes.Objective 3:The CESM is an improved version of the coupled-carbon-climate model. The DOE/NSF CESM is the latest version of the Community Climate System Model (CCSM), developed at the National Center for Atmospheric Research (NCAR). The model has atmospheric, ocean, land and sea ice components, linked together using a coupler. We focus here on the terrestrial biosphere model, the Community Land Model-Carbon Nitrogen (CLM-CN) model. Fires have been included originally in the CLM-CN based on a published fire algorithm. Further improvements to the soil and litter pools has been completed, and a beta version including these changes has been released to developers, with a move towards implementing a CN model based closely on the CENTURY SOC model being in progress for upcoming releases. Thus, working also with the CENTURY model, as proposed, will provide good synergy with ongoing efforts to improve the terrestrial C-N module of the CLM.As Objectives 1&2 provide results from testing the major hypothesized mechanisms for SOC priming, Objective 3 will take these results and use them to determine how these interactions should best be integrated into these box-flow soil carbon cycling models. In addition, as the magnitude and relative importance of these mechanisms across a range of environmental conditions are determined in Objective 1, Objective 2 will use these findings to constrain, calibrate and validate the models to include SOC priming interactions. The direct integration of these expansions into larger-scale Earth system models such as the CLM-CN will depend on the future development of other model components, such as pyC production from fires or different representations of plants, and thus may not happen immediately. However, the findings of this research are "model-agnostic" and will be directly applicable to similar SOC models including those already implemented in Earth system models, while the groundwork will be laid for its ultimate integration into these and other models.

Progress 08/01/14 to 07/31/18

Outputs
Target Audience:The results of this project will provided fundamental advances in understanding of the mechanisms underlying soil carbon cycling. It also demonstrated how these mechanistic insights affect predictions of long term soil organic carbon stocks with changes in global environment, land use, land management, and soil amendment. Given that soil organic carbon exchanges an order of magnitude more CO2 with the atmosphere annually than anthropogenic emissions, and that soil organic carbon is one of the most important determinants of soil health and fertility, these advances have wide-reaching implications for numerous fields, including soil science, agriculture, forestry, carbon sequestration, earth system modeling, climate change mitigation and adaptation, biochar, and soil biogeochemistry. As such our target audience comprises scientists and researchers in all of the above fields of study; policy makers interested in climate change or food security; engineers, industrialists and small businesses in the developing biochar industry; and agronomists, farmers and others interested in soil management to optimize for long term fertility and food security. The project team made presentations at the USDA Carbon Cycles meeting in Washington DC in 2015, in San Francisco in Fall 2016. In addition, the graduate student presented posters on priming mechanisms at EGU and AGU conferences from 2015 to 2017 as well as the trisociety meeting in 2016, and the postdoctoral associate an oral presentation on modeling priming at the AGU annual meeting in San Francisco. The PI gave an oral presentation on the modeling soil organic matter with microbial aspects on the global scale at the 2017 international soil organic matter meeting at Rothamsted, UK, as well as colloquia at the University of Wisconsin, Madison, in 2016, at Colorado State University in 2017 and at the University of Bayreuth in 2017. The PI also gave presentations to UN audiences at the UN Convention of the Parties in Marrakech and Bonn in 2016 and 2017 on soil organic carbon and their predictions. The PI organized an international workshop on soil organic matter modeling in 2018. Several publications have appeared in print, including by the graduate student, Silene DeCiucies, and several more are in preparation. The presentations at conferences, workshops and colloquia as well as scientific publications are the main avenues of communicating this work to audiences. Changes/Problems:The setup of the Picarro-enabled automated manifold system and program, while providing us with an unparalleled opportunity to continuously measure isotope values, has presented significant challenges. We had to restart our first experiment which delayed progress to gather experimental data by at least 6 months. In addition, we had to refine the water adjustments with the large additions of uncharred organic matter, and therefore had to repeat several short-term experiments, causing additional delay. We mitigated the issues we observed. The modeling study is in submission, and the final empirical manuscript is in revision after first submission to an international journal. What opportunities for training and professional development has the project provided?The project provided excellent opportunities for the female MS student (Silene DeCuices) supported by this grant to familiarize herself with scientific methodology, experiment planning, and scientific equipment and analysis (specifically isotope techniques and spectroscopic techniques such as nano-SIMS). She now has also attained great experience in data analyses using R, statistical analyses, data display and interpretation during this time of data analysis. Silene completed her graduate studies in early 2018, published on scientific manuscript (in the high-ranking journal Geochimica et Cosmochimica Acta) with one more manuscript in preparation. She obtained further experience in scientific presentation during our weekly laboratory meetings as well as during presentations at the American Geophysical Union (San Francisco), the trisociety and the European Geoscience Union (Vienna) meetings. In addition, one technician (Akio Enders) was provided with the opportunity to improve his design and analyses skills by designing and manufacturing an automated sampling device. He also obtained new skills in programming in python, and in troubleshooting very complex machinery. The postdoctoral associate, Dr. Dominic Woolf, gained advanced modeling experience as well as data handling experience using global data sets, and experience working with NCAR to utilize CLM and to add the new model to NCAR's testbed. How have the results been disseminated to communities of interest?Presentations were made at the Annual Researchers Meeting of the Carbon Cycles community Washington, DC, and in San Francisco, European Geosciences Union annual meetings in Vienna, Austria, the American Geophysical Union annual meetings in San Francisco, at the Biochar Conference at Cornell, at the Conference of the Parties of UNFCCC, and the international soil organic matter conference in Rothamsted, UK. We have also made steps to put our model into the testbed of NCAR, to make it publically available for comparison against other soil carbon models. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? During the project, we have addressed Objectives 1, 2 and 3 through reaching the following milestones: (a) Conducted experiments to identify and quantify the contribution of all major mechanisms contributing to negative and positive priming using our novel Picarro manifold system and investigated the spatial distribution of carbon using Nano-SIMS, using a wide variety of PyOM; (b) Tested the effects of charred in comparison to uncharred OM in soils with different organic matter contents; (c) Developed and refined a novel microbial model and calibrated it using a suite of long-term field experiments; (d) Compared the model performance against both field experiments and our own laboratory experiments; and (e) Conducted a global soil modeling effort using our novel model and compared the output to ISRIC's global soil data base. In addition, we published several papers that a help us interpret our priming data, explored additional mechanisms that we had not anticipated to possibly play a role and refined the methodology. We conducted highly mechanistic and detailed experiments that probed co-metabolism, dilution, substrate switching, inhibition, and surface stabilization as possible mechanisms that would affect native organic carbon after additions of charred and uncharred organic matter additions. In support of these experiments, we grew the 13-C enriched biomass including woody biomass (willow) and grassy biomass (Brachypodium) under an elevated 13-carbon dioxide atmosphere in growth chambers. We designed and manufactured a unique continuous sampling manifold that can automatically change the measurement between 120 flasks with minimal dilution of the headspace. Computer controls using R scripts were programmed and the hardware assembled and connected with the Picarro installation. We found clear evidence for all of the listed mechanisms except inhibition. Additions of uncharred organic matter additions caused mainly substrate switching and co-metabolism, with typically greater mineralization of existing organic matter. In stark contrast, additions of charred organic matter typically showed lower mineralization of existing organic matter, with dilution and substrate switching explaining some of the effects. The largest effect, however, was surface interaction which was also demonstrated by adsorption isotherms and direct observation through nano-SIMS. Organic matter charred at very low temperatures, however, had high metabolizable organic carbon that rather showed dynamics reminiscent if uncharred organic matter. Boreal and temperate soil O horizons behaved fundamentally different than the mineral horizons. The organic-rich and mainly mineral-free horizons did not show negative priming, even if the organic material was mixed with organic-free subsoils. In contrast, positive priming by additions of uncharred organic matter was greater in carbon-poor subsoils than carbon-rich topsoils, conforming to basic theory and prior experimental evidence that subsoils are deplete of easily mineralizable organic matter and influx of DOC may cause co-metabolism. We developed a soil carbon model that uses microbial population and activity dynamics to account for observed soil carbon turnover rates, including priming by OM additions. This is significant because soil-atmosphere feedbacks represent one of the largest uncertainties in current climate models. Current Earth Systems models rely on SOM models based on independent carbon pools exhibiting 1st order decay dynamics. It has long been recognised that such models do not accurately describe soil processes (for example, their inability to account for observed priming interactions), and a number of researchers advocate that next generation models need to incorporate microbial dynamics - whereby microbial biomass is not just an independent soil carbon pool, but is actively involved in the decomposition process. However, previous such modeling efforts have not adequately met the quality criteria required for Earth System models. Namely that they should (a) robustly/accurately describe data from long term trials, (b) be computationally efficient for large number of iterations involved in climate modeling, and (c) have sufficiently simple parameterisation that they can be run on spatially-explicit data available at global scale under varying conditions of global change over long time scales. The model that has been developed under this project meets these criteria while simultaneously predicting priming and eliminating the need to postulate physically-implausible passive or inert soil carbon pools. Unlike current de facto standard models such as DayCent or RothC which are only able to explain the observed longevity of soil carbon by introducing an ad hoc assumption that some soil carbon has an intrinsic mean residence time of centuries or longer, the new model developed here is able to explain the observed age of soil carbon from simple principles of microbial ecology and without the need for long turnover times in specific pools. Our novel model was refined by using improved functions for carbon use efficiency and behaved well using a range of published long-term datasets (r2=0.92; n=90). In comparison to a validation set, the correlation coefficient was comparable to the best calibration using standard pool models such as RothC. Comparison with our experimental incubation data showed that the trend in carbon dioxide emissions was reproducible, when we induced priming by additions of organic matter. When we ran our model with global organic matter input, soil properties and climate using the CLM data, we observed a very reasonable reproduction of global soil carbon distribution compared to the ISRIC harmonized soil database (HWSD) (rmse=4.7 kg C/m2; p<0.0001). Total global stocks of SOC in the top 0.3 m predicted by the model were 822 Pg C, which is also within the range of values derived from the HWSD (817 Pg C), GSOC (673 Pg C), SoilGrids (1190 Pg C), and the FAO/UNESCO Soil Map of the World (684-724 Pg C).

Publications

  • Type: Journal Articles Status: Published Year Published: 2018 Citation: DeCiucies S, Whitman T, Woolf D, Enders A and Lehmann A 2018 Priming mechanisms with additions of pyrogenic organic matter to soil. Geochimica et Cosmochimica Acta 238, 329-342.
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Sun T, Levin BDA, Schmidt MP, Guzman JJL, Enders A, Martinez CE, Muller DA, Angenent LT and Lehmann J 2018 Simultaneous quantification of electron transfer by carbon matrices and functional groups in pyrogenic carbon. Environmental Science and Technology 52, 8538?8547.


Progress 08/01/16 to 07/31/17

Outputs
Target Audience:The results of this project will provide fundamental advances in understanding of the mechanisms underlying soil carbon cycling. It will also demonstrate how these mechanistic insights affect predictions of long term soil organic carbon stocks with changes in global environment, land use, land management, and soil amendment. Given that soil organic carbon exchanges an order of magnitude more CO2 with the atmosphere annually than anthropogenic emissions, and that soil organic carbon is one of the most important determinants of soil health and fertility, these advances will have wide-reaching implications for numerous fields, including soil science, agriculture, forestry, carbon sequestration, earth system modeling, climate change mitigation and adaptation, biochar, and soil biogeochemistry. As such our target audience is expected to comprise scientists and researchers in all of the above fields of study; policy makers interested in climate change or food security; engineers, industrialists and small businesses in the developing biochar industry; and agronomists, farmers and others interested in soil management to optimize for long term fertility and food security. The project made a presentation at the USDA Carbon Cycles meeting in San Francisco in Fall 2016. In addition, the graduate student presented a poster on the priming dilution mechanism, and the postdoctoral associate an oral presentation on modeling priming at the AGU annual meeting in San Francisco. The PI gave an oral presentation on the modeling soil organic matter with microbial aspects on the global scale at the 2017 international soil organic matter meeting at Rothamsted, UK. These presentations at conference proceedings as well as future publications are the main avenues of communicating this work to an audience. Changes/Problems:The setup of the Picarro-enabled automated manifold system and program, while providing us with an unparalleled opportunity to continuously measure isotope values, has presented significant challenges. We had to restart our first experiment which delayed progress to gather experimental data by at least 6 months. In addition, we had to refine the water adjustments with the large additions of uncharred organic matter, and therefore had to repeat several short-term experiments, causing additional delay. We have by now mitigated the issues we have so far observed. What opportunities for training and professional development has the project provided?The project continues to provide an excellent opportunity for one female MS student (Silene DeCuices) to familiarize herself with scientific methodology, experiment planning, and scientific equipment and analysis (specifically isotope techniques and spectroscopic techniques such as Nano-SIMS). She now has also attained great experience in data analyses using R, statistical analyses, data display and interpretation during this time of data analysis. Silene is expected to have her MS exam later this year. She obtained further experience in scientific presentation during our weekly laboratory meetings as well as during presentations at the American Geophysical Union. In addition, one technician (Akio Enders) was provided with the opportunity to improve his design and analyses skills by designing and manufacturing an automated sampling device. He also obtained new skills in programming in python, and in troubleshooting very complex machinery. How have the results been disseminated to communities of interest?Presentations were made at the Annual Researchers Meeting of the Carbon Cycles community in San Francisco, the American Geophysical Union annual meetings in San Francisco, and international soil organic matter conference in Rothamsted, UK. We have also made steps to put our model into the testbed of NCAR, to make it publically available for comparison against other soil carbon models. What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, we will complete our incubation experiments investigating the effects of charred and uncharred substrate additions on the cycling of existing organic matter and the microbial community, capitalizing on a DIGG grant. We will continue to analyze our data using nano-SIMS at PNNL. The graduate student will write up the completed set of incubation experiments in two manuscripts and submit it for publication. The model will be published using a calibration and validation using a broader range of experimental data from a global network of existing long term trials as well as the global carbon distribution using ISRIC's dataset. In addition, we will apply the model to capture short-term priming dynamics and demonstrate its aptness to describe short-term local as well as long-term global soil organic carbon dynamics.

Impacts
What was accomplished under these goals? During this year of the project, we have accomplished five milestones towards Objectives 1, 2 and 3: (a) Conducted experiments to identify and quantify the contribution of all major mechanisms contributing to negative and positive priming using our novel Picarro manifold system and investigated the spatial distribution of carbon using Nano-SIMS; (b) Tested the effects of a range of PyOM materials in soils with different organic matter contents; (c) Refined the novel microbial model and calibrated it using a suite of long-term field experiments; (d) Compared the model performance against both field experiments and our own laboratory experiments; and (e) Conducted a global soil modeling using our novel model and compared the output to ISRIC's global soil data base. In addition, we published several ancillary papers that a help us interpret our priming data, explore additional mechanisms that we had not anticipated to possibly play a role and refine the methodology. We conducted experiments that probed co-metabolism, dilution, substrate switching, inhibition, and surface stabilization as possible mechanisms that would affect native organic carbon after additions of charred and uncharred organic matter additions. We found clear evidence for all of these mechanisms except inhibition. Uncharred organic matter additions showed mainly substrate switching and co-metabolism, with typically greater mineralization of existing organic matter. Additions of charred organic matter typically showed lower mineralization of existing organic matter, with dilution and substrate switching explaining some of the effects. The largest effect, however, was surface interaction which was also demonstrated by adsorption isotherms and direct observation through Nano-SIMS. Organic matter charred at very low temperatures, however, had high metabolizable organic carbon that rather showed dynamics reminiscent if uncharred organic matter. Boreal and temperate soil O horizons behaved fundamentally different than the mineral horizons. The organic-rich and mainly mineral-free horizons did not show negative priming, even if the organic material was mixed with organic-free subsoils. In contrast, positive priming by additions of uncharred organic matter was greater in carbon-poor subsoils than carbon-rich topsoil's, conforming to basic theory and prior experimental evidence that subsoils are deplete of easily mineralizable organic matter and influx of DOC may cause co-metabolism. Our novel model was refined by using improved functions for carbon use efficiency and behaved well using a range of published long-term datasets. In comparison to a validation set, the correlation coefficient was comparable to the best calibration using standard pool models. Comparison with our experimental incubation data showed that the trend in carbon dioxide emissions was reproducible, when we induced priming by additions of organic matter. When we ran our model with global organic matter input, soil properties and climate using the CLM data, we observed a very reasonable reproduction of global soil carbon distribution compared to the ISRIC harmonized soil database.

Publications

  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Ahmed ZU, Woodbury PB, Sanderman J, Hawke B, Jauss V, Solomon D, and Lehmann J 2017 Assessing soil carbon vulnerability in the Western USA by geo-spatial modeling of pyrogenic and particulate carbon stock. Journal of Geophysical Research  Biogeosciences 122, 354369.
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Dai Z, Webster TM, Enders A, Hanley K, Xu J, Thies JE and Lehmann J 2017 DNA extraction efficiency from soil as affected by pyrolysis temperature and extractable organic carbon of high-ash biochar. Soil Biology and Biochemistry 115, 129-136.
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Sun T, Levin BDA, Guzman JJL, Enders A, Muller DA, Angenent LT and Lehmann J 2017 Rapid electron transfer by the carbon matrix in natural pyrogenic carbon. Nature Communications 8, 14873.
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Whitman T, Pepe-Ranney C, Enders A, Koechli C, Campbell A, Buckley D, and Lehmann J 2016 Dynamics of microbial community composition and soil organic carbon mineralization in soil following addition of pyrogenic and fresh organic matter. Nature ISME Journal 10, 2918-2930.
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Woo SH, Enders A and Lehmann J 2016 Microbial mineralization of pyrogenic organic matter in different mineral systems. Organic Geochemistry 98, 18-26.


Progress 08/01/15 to 07/31/16

Outputs
Target Audience:The results of this project will provide fundamental advances in understanding of the mechanisms underlying soil carbon cycling. It will also demonstrate how these mechanistic insights affect predictions of long term soil organic carbon stocks with a changes in global environment, land use, land management, and soil amendment. Given that soil organic carbon exchanges an order of magnitude more CO2 with the atmosphere annually than anthropogenic emissions, and that soil organic carbon is one of the most important determinants of soil health and fertility, these advances will have wide-reaching implications for numerous fields, including soil science, agriculture, forestry, carbon sequestration, earth system modeling, climate change mitigation and adaptation, biochar, and soil biogeochemistry.. As such our target audience is expected to comprise scientists and researchers in all of the above fields of study; policy makers interested in climate change or food security; engineers, industrialists and small businesses in the developing biochar industry; and agronomists, farmers and others interested in soil management to optimize for long term fertility and food security. The project made a presentation at the USDA Carbon Cycles meeting in Washington DC, and started coordinating efforts with related projects in the US. In addition, the graduate student presented a poster on the project plans at the session on priming held at the 2015 European Geosciences Union Annual Meeting in Vienna, Austria, which was very helpful in refining the experimental plan. This year, the graduate student presented preliminary data at the Cornell Biochar Conference and plans to present at the Tri-Societies meeting in the fall. These presentations at conference proceedings as well as future publications are the main avenues of communicating this work to an audience. Changes/Problems:The setup of the Picarro-enabled automated manifold system and program, while providing us with an unparalleled opportunity to continuously measure isotope values, has presented significant challenges. We had to restart our first experiment which delayed progress to gather experimental data by at least 6 months. What opportunities for training and professional development has the project provided?The project has provided the opportunity for one female MS student (Silene DeCuices) to familiarize herself with scientific methodology, experiment planning, and scientific equipment and analysis (specifically isotope techniques). She obtained skills in specific engineering with the development of the analyzer, and skills in programming and data analysis with the ongoing data collection. She obtained experience in scientific presentation during our weekly laboratory meetings as well as during presentations at the European Geosciences Union Convention in Vienna, and in the Biochar Conference at Cornell in Spring 2016 where she represented the project. In addition, one technician (Akio Enders) was provided with the opportunity to improve his design and analyses skills by designing and manufacturing an automated sampling device. He also obtained new skills in programming in python, and in troubleshooting very complex machinery. How have the results been disseminated to communities of interest?Presentations were made at the Annual Researchers Meeting of the Carbon Cycles community in Washington, DC, the European Geosciences Union annual meetings in Vienna, Austria, and at the Biochar Conference at Cornell. What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, we will conduct at least two further incubation experiments investigating the effects of biochar and uncharred substrate additions on the cycling of existing organic matter. We will also analyze our data using nano-SIMS at PNNL, and will write up the current incubation experiment. Calibration and validation of the soil carbon model will continue to be improved by using a broader range of experimental data as they become available, in combination with a large set of data from a global network of long term trials that has already been collated. The gold standard that any soil carbon model must fulfill before it can be considered for use in Earth system models is that it must be able to accurately describe data from long term trials, and that it must be able to accurately predict current geographic distributions of soil carbon stocks globally. The next phase of model development is to demonstrate the model's robustness with regard to these critical tests, and to publish the results.

Impacts
What was accomplished under these goals? During this year of the project, we have accomplished five milestones towards Objectives 1, 2 and 3: (a) Completed the installation and programming of the cavity ring down infrared CO2/CH4 isotope analyzer; (b) Completed software development for data extraction, analysis and visualization; (c) completed the first 3 month incubation experiment; (d) started a second incubation experiment; and (e) a novel soil carbon model has been developed that incorporates microbial dynamics. In addition, we published a methods study in Nature Communications showing how to distinguish three carbon sources using only two isotopes (12C and 13C). Installation of the continuous gas isotope analyser: we designed and manufactured a unique continuous multiplexed sampling system to automatically switch between up to 120 parallel sample microcosms, with minimal dilution of the gas headspace. Software was written in Python to control the sample multiplexing manifold and interface it with a Picarro G2201-I CO2/CH4 isotope analyser. Software was developed and tested using an interactive Agile Scrum development methodology to optimize for accuracy, long-term reliability of the sampling system and security through incremental data backup on a cloud platform. The sampling and analysis apparatus was calibrated and tested using different known quantities of calibration standard gas mixtures to verify the accuracy of the mechanics and programming. Automated data extraction and analysis software has been written in the R statistical programming language to sort, organize, condense, visualize the data from the analyser, and to perform statistical analysis of treatment effects. The sampling apparatus records data approximately twice per second continuously over three to four months, so it is imperative to have an efficient system for optimized for big data. This type of data processing is ideal because each step can be tracked back to a published script, and reproduced if necessary. Completed a 3-month incubation experiment: This incubation was designed to both answer questions in our objectives, and to further troubleshoot the analyser and data collection system as a whole. We focused on the variables of char application rate, soil texture, and initial carbon content of soil used. We used the highly labelled substrate that was grown the year before, and the soils used were a local silt loam subsoil, and a boreal forest organic horizon from Sweden. Variables of pH and nutrient content were controlled for. Both of these soils have been used extensively in previous experiments, so were useful in data checking and comparisons. Data from this incubation enabled us to improve the analysis method, and decide upon an ideal substrate addition rate for future experiments. We found that priming effects were significant in soils with higher initial carbon contents, which will contribute to future experimental design. Second incubation experiment: The second incubation uses soils with higher carbon contents based on our previous results, and is focused on the variables of pyrolysis temperature of the pyC substrate additions, labile carbon in the substrate additions, and carbon content of the soil used. We are also investigating the impact of non-pyrolysed substrates in this second incubation period using a factorial design with several application rates, and with varying pH and labile carbon content. This incubation is ongoing, and will contribute to objectives 1 and 2. A soil carbon model has been developed that uses microbial population and activity dynamics to account for observed soil carbon turnover rates, including priming by OM additions. This is significant because soil-atmosphere feedbacks represent one of the largest uncertainties in current climate models. Current Earth Systems models rely on SOM models based on independent carbon pools exhibiting 1st order decay dynamics. It has long been recognised that such models do not accurately describe soil processes (for example, their inability to account for observed priming interactions), and a number of researchers advocate that next generation models need to incorporate microbial dynamics - whereby microbial biomass is not just an independent soil carbon pool, but is actively involved in the decomposition process. However, previous such modeling efforts have not adequately met the quality criteria required for Earth System models. Namely that they should (a) robustly/accurately describe data from long term trials, (b) be computationally efficient for large number of iterations involved in climate modeling, and (c) have sufficiently simple parameterisation that they can be run on spatially-explicit data available at global scale under varying conditions of global change over long time scales. The model that has been developed under this project meets these criteria while simultaneously predicting priming and eliminating the need to postulate physically-implausible passive or inert soil carbon pools. Unlike current de facto standard models such as DayCent or RothC which are only able to explain the observed longevity of soil carbon by introducing an ad hoc assumption that some soil carbon has an intrinsic mean residence time of centuries or longer, the new model developed here is able to explain the observed age of soil carbon from simple principles of microbial ecology.

Publications

  • Type: Journal Articles Status: Published Year Published: 2015 Citation: Whitman, T. and Lehmann, J. 2015. Three-source partitioning with two stable isotopes is a powerful tool for the biogeochemical toolbox. Nature Communications, 6, 8708 doi:10.1038/ncomms9708.


Progress 08/01/14 to 07/31/15

Outputs
Target Audience:The project made a presentation at the USDA Carbon Cycles meeting in Washington DC, and started coordinating efforts with related projects in the US. In addition, the graduate student presented a poster on the project plans at the session on priming held at the 2015 European Geosciences Union Annual Meeting in Vienna, Austria, which was very helpful in refining the experimental plan. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project has provided the opportunity for one female MS student (Silene DeCuices) to familiarize herself with scientific methodology, experiment planning, and scientific equipment and analysis (specifically isotope techniques). She obtained experience in scientific presentation during our weekly laboratory meetings as well as during a poster presentation at the European Geosciences Union in Vienna, where she represented the project. In addition, one technician (Akio Enders) was provided with the opportunity to improve his design and analyses skills by designing and manufacturing an automated sampling device. How have the results been disseminated to communities of interest?Presentations were made at the Annual Researchers Meeting of the Carbon Cycles community in Washington, DC, and at the European Geosciences Union annual meetings in Vienna, Austria. What do you plan to do during the next reporting period to accomplish the goals?During the next reporting period, we will conduct at least two incubation experiments investigating the effects of biochar on the cycling of existing organic matter. We also plan to start one trial that includes plants to study three-way interactions for which we completed the data analyses.

Impacts
What was accomplished under these goals? During the first year of the project, we accomplished four tasks that are required to undertake Objectives 1 and 2: (a) Growth of the 13-C enriched biomass; (b) production of the biochar; (c) collection of soils; and (d) installation of the continuous isotope gas measurement equipment.In addition, we completed a methods study to be able to distinguish three carbon sources using only two isotopes (12C and 13C), which we submitted for publication. Growth of the 13-C enriched biomass: a woody biomass (willow) and grassy biomass (Brachypodium) was grown under an elevated 13-CO2 atmosphere in growth chambers from September 2014 through January 2015. Sufficient biomass was produced to complete the project. Isotope contents were measured for various batches and plant parts, and cuttings identified with high enrichment (above 1000 ppm delta 13C) and intermediate enrichment (between 300-1000 ppm delta 13C) that will be used for different experiments. Production of the biochar: biochar was produced at different temperatures with the woody and grassy biomass using a batch kiln under argon atmosphere with run times at highest temperature of 20 minutes. Collection of soils: soils were collected from a previous experiment for which we have a wealth of experience with respect to priming interactions. In addition, we obtained an organic horizon from a boreal forest in Sweden, where large positive priming was reported, and we are about to collect highly weathered soils from the Calhoon Forest site. Installation of the continuous isotope gas measurement equipment: we designed and manufactured a unique continuous sampling manifold that can automatically change the measurement between 120 flasks with minimal dilution of the headspace. Computer controls using R scripts were programmed and the hardware assembled and connected with the Picarro installation. We have shared the design with another project in the Carbon Cycles cohort and see great potential for the system to facilitate experimentation in laboratory incubations. The system has been tested between May and June 2015 and is by now ready to be used for the first incubations.

Publications

  • Type: Conference Papers and Presentations Status: Published Year Published: 2015 Citation: DeCiucies S, Dharmakeerthi S, Whitman T, Woolf D and Lehmann J 2015 Priming of native soil organic matter by pyrogenic organic matter. Geophysical Research Abstracts Vol. 17, EGU2015-7968