Belowground Biogeochemistry
Developing predictive understanding of belowground biogeochemistry and improving terrestrial ecosystem modeling capabilities
Belowground Biogeochemical Cycles. The plant-soil-microbe system. Key: CO2, carbon dioxide; N, nitrogen; P, phosphorus; C, carbon; DOC, dissolved organic carbon. [Courtesy Lawrence Berkeley National Laboratory]
Principal investigator: Margaret Torn
The biogeochemical functioning of soils is critical for supporting plant growth, controlling the water cycle, and regulating local and global nutrient cycles. Biogeochemical cycling involves microbial, plant, and abiotic processes responsible for soil organic matter (SOM) chemistry, transformation, and loss, which are also intimately coupled to nitrogen availability to plants and microbes.
Accurate understanding of these soil biogeochemical processes is critical for predicting ecosystem responses to environmental changes, but current gaps in understanding of soil-plant-microbe interactions make estimates of these responses highly uncertain. Moreover, subsoils contain twice as much carbon as surface horizons globally, yet their contribution to ecosystem biogeochemistry has largely been ignored.
To address these challenges, the Environmental System Science (ESS) program of the Department of Energy’s (DOE) Biological and Environmental Research (BER) Program is supporting the Belowground Biogeochemistry Science Focus Area (SFA) led by Lawrence Berkeley National Laboratory.
This SFA aims to develop a predictive understanding of belowground biogeochemistry in the soil-plant-microbe-climate system, with an emphasis on the whole soil profile, and to improve capabilities for modeling terrestrial ecosystems. To accomplish these goals, this SFA integrates a team of experts in biogeochemistry and ecosystem ecology, microbial ecology and genomics, geochemistry, and ecosystem modeling.
Blodgett Forest Whole-Soil Manipulation. In the central experiment of the Belowground Biogeochemistry Science Focus Area, the whole profile of a forest soil is manipulated by 4ºC year-round to examine decomposition pathways, microbial processes, and long-term stabilization. [Courtesy Lawrence Berkeley National Laboratory]
Key Science Questions
The overarching challenge driving the Belowground Biogeochemistry SFA is developing predictive understanding of soils’ role in ecosystem processes over a range of timescales. Specific science questions to address this challenge include:
- How do biotic and abiotic processes and properties interact to control soil organic matter (SOM) cycling?
- How do SOM cycling and coupled soil-microbe-plant biogeochemistry respond to whole-profile manipulations over time and space?
- What is the potential for whole-profile soil organic carbon changes over the 21st century?
- What is the best way to represent a generalized set of principles governing soil carbon dynamics and nutrient cycling to improve ecosystem models?
Research Approach
Scientists are employing a coordinated set of field and laboratory experiments, combined with advanced analytical techniques and process-rich modeling, to characterize controls on organic matter cycling as shaped by interactions between soils, plants, microbes, and nutrient cycling. Model uncertainties guide the experimental design and observational priorities, while empirical results and theory inform model development to address the challenges of spatial and temporal scaling. Research focuses on the whole-soil profile, and whole-soil manipulation experiments serve as an integrating platform to study belowground biotic and abiotic processes governing ecosystem biogeochemical cycles.
Research Tasks and Recent Results
Grassland Whole-Soil Manipulation. The Science Focus Area is starting a comparison whole-soil manipulation experiment in a grassland to study coupled plant processes and nitrogen cycling. [Courtesy Lawrence Berkeley National Laboratory]
Task 1 creates and maintains long-term, whole-soil manipulation experiments in the field and measures emergent responses, such as soil respiration and nutrient availability. Results are showing that soil temperature has a large effect on decomposition and SOM composition at all depths. Warming by 4°C increased respiration by about 35%, a temperature sensitivity higher than that predicted by most Earth system models. To study temporal responses, the SFA added additional experimental plots seven years after the original started.
Task 2 determines how soil microbial traits, physiology, and community properties vary over the soil profile; respond to the environment; and affect SOM mineralization rates, pathways, and products. SFA research indicates warming results in a significant decline in microbial biomass in subsoils, lower substrate use efficiency, and thereby decreasing biomass.
Task 3 examines how SOM chemical composition and the interactions of organic molecules with minerals and metals influence SOM availability to soil microbial transformations and leaching. In recent results, mineral stabilization explains long-term persistence of even the most labile substrates. Decomposition of labile substrates was effectively stopped when they were sorbed to mineral surfaces.
Task 4 improves modeling of decomposition, nitrogen cycling, and plant growth. New process representations, including for microbial activity, nutrient limitations, and the effects of moisture and temperature on organo-mineral interactions, are being incorporated into DOE’s Energy Exascale Earth System Model (E3SM) Land Model (ELM). This is important for benchmarking model performance against perturbation experiments and for exploring ecosystem dynamics at site to global scales. An international data synthesis activity co-led by the SFA will use results from similar manipulation experiments around the world to build understanding and evaluate models, thereby improving confidence in assessments of ecosystem carbon storage.
Task 5 explores the impacts of wildfire and soil warming on soil biogeochemistry and forest regeneration. The SFA is developing a novel rapid-response manipulation approach and plans to deploy it postfire in a proof-of-concept experiment focused on belowground biogeochemistry and tree seedling establishment in a mid-elevation Sierra Nevada Forest.
Science Focus Area (SFA) Research Organization. The Belowground Biogeochemistry SFA is organized into five main tasks with field and laboratory experiments tightly coupled with modeling to enable predictive understanding of belowground processes governing terrestrial biogeochemical cycles. [Courtesy Lawrence Berkeley National Laboratory]
Model Integration
The Belowground Biogeochemistry SFA employs process-rich, fine-scale models, as well as representations for global applications. This approach enables the exploration of mechanisms at the scale of observations and the extraction of efficient process representation for integration into DOE’s ELM. The long-term vision is a modeling capability that can be applied across temporal and spatial scales, providing insights into transient results such as soil response to various manipulations and the effect of altered nutrient cycling on plant inputs to soil. The SFA will test the models across a wide range of soil types, chemistries, plant inputs, conditions, and manipulations.
2024 Abstracts
Videos
Basics2Breakthroughs: Warmer temperatures effect on grasslands
A LBNL postdoctoral researcher, Elaine Pegoraro, explains how they study the impacts of warming and carbon release from terrestrial ecosystems.
Dr. Margaret Torn - What I'm Discovering
Dr. Margaret Torn shares ideas and questions about what to do as our planet warms and how ecosystems could be part of the solution.
Dr. Margaret Torn - What I'm Working On
Dr. Margaret Torn explains what her team has found as a result of studying how warming soil temperatures impact soil microbe activity and carbon cycling in the Sierra Nevada.
