Performing Department
(N/A)
Non Technical Summary
Increasing carbon storage in soil can help combat climate change by offsetting emissions from fossil fuel combustion. The Colombian Orinoquía is a vast savannah ecosystem with huge potential to store carbon via implementation of deep-rooted grass cultivars. These grasses produce large root biomass and can "pump" carbon deep into the soil. However, they require adequate provision ofnutrients to avoid soil degradation and loss of previously stored carbon. Because over-application of mineral fertilizers can harm the environment and lead to greenhouse gas emissions, sustainable strategies are needed that promote nutrient uptake by grasses in Orinoquía pasture systems. A promising strategy for sustainable nutrient management is to promote symbiotic relationships between deep-rooted grasses and arbuscular mycorrhizal fungi (AMF). AMF feed on carbon released by plant roots and, in return, provide plants with nutrients obtained from the soil. With AMF, there is the added benefit that they have been shown to contribute to soil carbon storage via transformation of soil organic matter into stable forms. Yet, it is also known that AMF can trigger soil processes that lead to carbon mineralization as they mine soil for nutrients. To determine the true potential of AMF as a sustainable strategy to improve nutrient uptake by deep-rooted grasses and increase carbon storage in Orinoquía pastures, it is essential to characterize the mechanisms through which AMF may induce losses of soil carbon.In this project, the deep-rooted grass cultivar Urochloa humidicola will be grown in pots of Orinoquía soil. In five of the pots, plants will first undergo root inoculation with AMF. In the other five pots, plants will receive no inoculation. For each pot, total plant nutrient uptake and emission of CO2 will be determined. During this experiment, a wide array of soil chemical parameters (e.g., pH, dissolved nutrients, plant- and fungal-derived organic compounds) will be measured. These measurements will be performed at the microscale, to target the small compartment of soil surrounding plant roots where mineralization of stable carbon is known to primarily take place. By comparing results between treatments without vs. with AMF inoculation, we will elucidate the exact soil processes through which AMF may lead to loss of highly stable soil carbon. As a further step, we will use process-based modeling to evaluate the extent that these microscale processes contribute to our measured emissions of CO2. Overall, this project will provide essential mechanistic understanding of how AMF affect the microscale soil processes that control carbon storage. This fundamental knowledge is necessary to evaluate whether increased nutrient uptake in deep-rooted grasses with AMF may occur at the expense of soil carbon storage in tropical pastures. Moving forward, the results of this project will serve as a basis for agronomists, farmers, and policy makers to approach the urgent question of grasslands management for climate mitigation in the vast Orinoquía.
Animal Health Component
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Research Effort Categories
Basic
100%
Applied
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Developmental
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Goals / Objectives
The main purpose of this project is to provide detailed mechanistic knowledge of how arbuscular mycorrhizal fungi (AMF) affect the microscale soil processes that control carbon mineralization in tropical pasture systems.Goal 1: The first scientific goal is to evaluate how mineral-solubilizing organic compounds affect rhizosphere processes contributing to destabilization of mineral-organic associations (MOA) without vs. with AMF inoculation. Within goal 1 are the following objectives:To collect soil from Orinoquía improved pastures and import this into the US, for use in laboratory experimentsTo perform a pot experiment to identify the AMF inoculation strategy that results in (1) root infection of forage grasses (i.e., the deep-rooted grass cultivar Urochloa humidicola) and (2) alters CO2 release from soil compared to the non-AMF-inoculated controlTo perform a rhizobox experiment in which deep-rooted grass cultivar Urochloa humidicola is grown in Orinoquía soil both without and with AMF inoculation; to collect microscale geochemical data, sample soil solution, and collect plant-growth data at high time-resolution during this experimentTo characterize mineral-solubilizing organic compounds in rhizosphere soil solution samples using liquid chromatography coupled to ultrahigh resolution mass spectrometry (LC-UHRMS)To determine whether there are differences in mineral-solubilizing organic compounds identified with LC-UHRMS without vs. with AMF inoculationTo determine whether composition of mineral-solubilizing organic compounds is linked to geochemical evidence of MOA destabilization (e.g., parameters such as pH, DOC, dissolved iron), to establish whether AMF inoculation increases organic compounds released by plants and microbes that trigger MOA destabilization processes in the rhizosphereGoal 2: The second scientific goal is to characterize the key driving processes through which AMF affect MOA destabilization and bulk carbon mineralization. Within this goal are the following objectives:To use geochemical and plant-growth data collected during the rhizobox experiment (goal 1, objective 3) to calibrate the existing reactive transport model, Root Exudation in Watershed-scale Transport paired with Crunch (REWT-Crunch)To pair the Root Exudation in Watershed-scale Transport model with the reactive transport model PHT3D, allowing incorporation of iron speciation into model calculations; to calibrate the REWT-PHT3D model using geochemical and plant-growth data collected during the rhizobox experiment (goal 1, objective 3)To use both REWT-Crunch and REWT-PHT3D to evaluate to what extent microscale geochemical data collected during the rhizobox experiment can explain observed bulk-scale variations in carbon mineralization (i.e., CO2 release) without vs. with AMF inoculationTo compare the results of REWT-Crunch and REWT-PHT3D to validate/evaluate the role of soil iron speciation in the model calculationsGoal 3: A milestone of this project will be dissemination of the project findings to the international scientific community in a way that demonstrates the project's high impact and advancement of the field. Within this goal are the following objectives:To publish two scientific manuscripts in high-impact, peer-reviewed journalsTo present the findings of this project at two scientific conferences during the project period (Soil Ecology Society conference in May 2026, Soil Science Society of America conference in November 2026)To discuss findings with colleagues (from the University of Minnesota, Alliance Bioversity International - CIAT, previous colleagues from Switzerland and Germany, new connections made at conferences, etc.) to improve results interpretation, evaluation of project impact, and develop ideas for future work based on the results of this projectGoal 4: An important outreach goal of this project is close collaboration and discussion with local and regional stakeholders in Colombia. This is needed to ensure the results of this project will be used to develop land management practices in Orinoquía pasture systems that promote carbon sequestration. Within this goal are the following objectives:To work with collaborator Dr. Jacobo Arango (senior scientist in the tropical forages program of Alliance Bioversity International - CIAT) to develop strong communication and connections with principal stakeholders, including farmers, researchers, policy makers, and members of the private sector, all of whom have strong vested interests in improved agronomic management of Orinoquía pasture systemsTo complete three meetings with principal stakeholders over the course of the project periodFirst meeting: discuss the planned project, obtain feedbackSecond & third meetings: communicate results obtained, and discuss how these results may inform future projects to evaluate land management practices in the OrinoquíaTo continue to perform outreach, maintain connections, and communicate project results to principal stakeholders long after the project period has endedGoal 5: Another goal of this project is to communicate results to youth and young scientists locally in Minnesota and the US, to promote engagement with agricultural sciences. Within this goal are the following objectives:To run workshops in the University of Minnesota's K-12 program to inspire young students to engage with soil science and agronomyTo present the results of this project at departmental events for young researchers (undergraduate-, master's-, and PhD-level) at the University of Minnesota's Department of Chemistry and Department of Soil, Water, and ClimateTo mentor 1-2 undergraduate students who will perform research projects to support the overall research goals of this projectGoal 6: The final goal of this project is to allow the Project Director, Dr. Jill Bachelder, to develop the skills and research portfolio needed for a career as a professor at an R1 institution in the US, i.e. in performing cutting-edge research that uses fundamental process elucidation studies to solve real-world challenges in agronomic systems. Within this goal are the following objectives:To successfully measures geochemical parameters at the microscale in a rhizobox experiment, gaining skills necessary to characterize microscale soil processesTo become an expert in using LC-UHRMS for analysis of plant- and microbe-derived organic compounds in soil, a skill that will be essential for her future researchTo become an experienced user of the reactive transport models REWTCrunch and REWT-PHT3D and to gain expert-level understanding of combining RTM with laboratory experiments for process elucidationTo plan soil sampling and effectively communicate research activities to collaborators at Alliance Bioversity International - CIAT and stakeholders in Colombia, thus gaining experience with organizing international collaborative projects that benefit local communities and research effortsTo gain experience teaching at the university level by presenting guest lectures in courses at the University of MinnesotaTo develop scientific writing and communication skills with mentor Prof. Rene Boiteau, by receiving feedback and training on all manuscripts and conference presentationsTo gain experience with grant proposal writing by working with mentor Prof. Rene Boiteau to learn essential skills for this (including identification of key research questions, definition of objectives, description of approach and rationale, and construction of a work plan, timeline, and budget)To expand professional networks to include researchers and stakeholders in the US and Colombia, for collaborations in future projects as an independent researcherTo develop full career independence by applying for academic positions (professorships at R1 institutions in the US) and career grants (e.g., NSF CAREER)
Project Methods
SCIENTIFIC METHODS:Preliminary work: Soil will be collected from the Hacienda San José (HSJ) field site in Orinoquía, Colombia by collaborating with Dr. Jacobo Arango (Alliance Bioversity International - CIAT). Sampled soil will be transported to the University of Minnesota (Boiteau Lab) under a valid soil import permit. An initial pot experiment will be performed in a biosafety growth chamber, to test three inoculation strategies, i.e. (1) inoculation with commercially-available AMF from a local supplier without prior soil sterilization; (2) cultivation of native AMF followed by soil inoculation without prior soil sterilization; (3) cultivation of native AMF followed by inoculation of sterilized soil. All inoculation strategies will have three treatments: a negative control (no AMF inoculant added), inoculated pots, and a positive control (autoclaved AMF inoculant added). In each treatment, deep-rooted grass cultivar Urochloa humidicola will be grown for 30 days. Ambient CO2 will be sampled every 48 hours. At harvest, plant parameters will be measured (root and shoot biomass, concentrations of carbon, nitrogen, phosphorus, and iron). The percentage of root area colonized by AMF will be evaluated via staining and light microscopy analysis. The inoculation strategy resulting in successful infection of plant roots and alteration of CO2 emission during the plant growth period will be chosen.Rhizobox experiment: A rhizobox experiment will be performed using a novel setup developed by the group of Prof. Marco Keiluweit. Using the optimum AMF inoculation strategy identified in "preliminary work", deep-rooted grass cultivar Urochloa humidicola will be grown in HSJ soil for 30 days. The rhizoboxes will be equipped with microsensors to measure geochemical parameters, i.e. pH, redox potential, and dissolved oxygen. The rhizoboxes will also contain microdialysis tubes for soil solution sampling. Microscale geochemical measurements and plant growth data will be collected with high time resolution, which is necessary for reactive transport modeling (see "work package 2"). Soil solution samples will be collected hourly during four 24-hour periods (days after sowing: 7, 14, 21, 28). Ambient CO2 will be measured once every 48 hours during plant growth. Microbial communities and iron speciation will be characterized in the starting soil and in rhizosphere soil collected at the end of the experiment. Data and samples from the rhizobox experiment will be used in work packages 1 and 2.Work package 1: Linking plant- and microbe-derived organic compounds to MOA destabilization. For soil solution samples from the rhizobox experiment, plant- and microbe-derived compounds will be characterized using liquid chromatography coupled to ultrahigh resolution mass spectrometry (LC-UHRMS). This is a highly advanced analytical technique for characterizing these compounds, which are very challenging to measure. Iron-binding agents (e.g., phytosiderophores, fungal and bacterial siderophores) will be identified following previously established analytical methods and data processing tools used in the Boiteau Lab. In the same measurement, LC-UHRMS will be used to quantify mineral-solubilizing organic acids (e.g., citrate, oxalate). The composition of plant- and microbe-derived organic compounds in the soil solution will be compared between treatments without vs. with AMF inoculation. This dataset will also be linked to biogeochemical parameters (e.g., pH, redox potential, dissolved organic carbon, dissolved iron) measured in the rhizobox experiment, as these are strong indicators of MOA dissolution.Work package 2: Reactive transport modeling (RTM). To identify key soil processes that determine the effect of AMF on soil carbon mineralization in improved pastures, RTM will be used. This follows a highly promising and emerging workflow of previous studies from Prof. Athena Nghiem (expert in combined RTM and laboratory measurements). To perform RTM, the root exudation in watershed-scale transport model paired to the RTM Crunch (REWTCrunch) will be used in collaboration with Prof. Praveen Kumar (expert in modeling of critical zone processes). Furthermore, the model REWT will be paired with PHT3D, another RTM, to incorporate iron speciation into the model, in collaboration with Prof. Nghiem (expert in PHT3D). The rhizobox experiment data collected for plant growth, soil geochemical parameters, and microbial communities will be used for calibration of both REWTCrunch and REWT-PHT3D using PEST ++, in collaboration with Prof. Nghiem. Then, both models will be used to "turn on" and "turn off" individual processes (e.g., root growth, root exudation, iron dissolution) to compare the net effect on carbon mineralization between treatments without vs. with AMF inoculation. In this way, it will be determined which modeled soil processes influenced by AMF inoculation have the greatest effect on carbon mineralization.EFFORTS:Formal classroom instruction by providing guest lectures during courses at the University of Minnesota, in which the results of this project will be presented as case studiesLaboratory instruction and mentorship of 1-2 undergraduate students who will contribute to this projectThree meetings with principal stakeholders during the project periodExtensive networking within local, regional, and international agronomic organizations, via colleagues at Alliance Bioversity International - CIAT and using the greater CGIAR networkPresentation of project results at two scientific conferences during the project periodEVALUATION:There will be four milestones during the project period, i.e. completion of preliminary work, the rhizobox experiment, work package 1, and work package 2. Completion of work package 1 will lead to the project outcome, "expanded library of known organic compounds that may be released by AMF in tropical degraded soil". Following this, the main evaluation factors indicating success of these research deliverables are (1) whether the project successfully identified how AMF inoculation affects the release of mineral-solubilizing plant- and microbe-derived organic compounds and (2) whether RTM could be used to identify key processes through which AMF affect carbon mineralization.The main research deliverables will be publication of two scientific manuscripts, which will be written and published during the second year of the project. This will result in two project outcomes, "Increased mechanistic understanding of the role of arbuscular mycorrhizal fungi in carbon mineralization in tropical degraded pastures" and "increased understanding of the potential for AMF management to promote carbon sequestration in Orinoquía improved pastures", as publications will allow dissemination of these discoveries to the greater scientific community.A key metric of project success will be the level of engagement with principal stakeholders. This will indicate the degree to which the fundamental results obtained in this project are valued by local communities and government agencies. High level of engagement and discussion between the Project Director, project collaborators, and principal stakeholders will greatly contribute to the project outcome, "increased awareness among principal stakeholders concerning the beneficial vs. detrimental effects of AMF management on carbon sequestration in Orinoquía improved pastures".Evaluations of project success will be communicated to project collaborators in regular written communications (every few months) and will be discussed at yearly project meetings. This will also be discussed with and disseminated to principal stakeholders yearly. The evaluation of project success will be disseminated to USDA-NIFA in yearly reports followed by a final report at the end of the project.