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Protecting climate-sensitive soil ecosystems
Review paper summarizes the effects of climate change on soil microorganisms and the ecosystem services they provide, and evaluates potential mitigation measures.
Researchers from Pacific Northwest National Laboratory reviewed the current state of knowledge about the impacts of climate change on soil microorganisms in different climate-sensitive soil ecosystems. They also examined the possibilities of using soil microorganisms to store carbon or inoculate plants to help mitigate the negative consequences of climate change. Based on their review, the authors recommend an integrated approach that combines beneficial properties of soil microorganisms with sustainable soil management practices to support plant production, maintain a clean water supply, sustain biodiversity, store carbon, and increase resilience in the face of a changing climate.
The effects of climate change on soil microbial communities have potentially large consequences for Earth's soil ecosystems and the beneficial services that soil microbiomes provide. This review highlights the need to connect the fine-scale details arising from microbiome studies to the landscape-scale resolution of many Earth system climate models in the search for climate change mitigation measures.
On Earth’s terrestrial surface, the soil microbiome cycles nutrients to sustain plant and animal life. While this microbial community is innately connected to environmental conditions, impacts on the soil microbiome due to climate change vary depending on the ecosystem. Different aspects of climate change impact soil microbial communities and their important ecosystem functions, such as cycling of carbon and supporting plant growth. But the molecular details of soil biochemical reactions responsible for these key functions are largely unknown.
Researchers synthesized existing knowledge of climate change impacts across a range of soil environments—permafrost, forests, grassland, wetlands, and deserts—to examine how the microbiome responds. They looked at microbial changes coinciding with different climate change variables including increases in carbon dioxide levels, temperatures, drought, flooding, and fires. Their review showed that microbial physiology largely determines the ability of soil ecosystems to adapt, and that some microbiomes may be suitable for climate change mitigation measures such as carbon sequestration and promoting plant growth. The review sets the stage for future research on soil microbiomes and challenges to overcome in order to connect to larger-scale predictive models of climate change.
Janet Jansson, Lab Fellow, firstname.lastname@example.org
Kirsten Hofmockel, Earth Scientist, email@example.com
This research was supported by the Department of Energy Office of Biological and Environmental Research (BER) Genomic Science Program and is a contribution of the Scientific Focus Area "Phenotypic response of the soil microbiome to environmental perturbations." PNNL is operated for DOE by Battelle Memorial Institute under Contract DE-AC05-76RLO1830. A portion of the research was performed using the Environmental Molecular Sciences Laboratory, a DOE Office of Science User Facility sponsored by BER and located at PNNL.
Nutrient-Hungry Peatland Microbes Reduce Carbon Loss Under Warmer Conditions
Enzyme production in peatlands reduces carbon lost to respiration under future high temperatures.
As atmospheric temperatures and carbon dioxide concentrations rise, photosynthesis by plants is expected to increase, leading to more photosynthate released by roots to the soil microbial community. Researchers from Pacific Northwest Northwest National Laboratory and Iowa State University examined the response of boreal peatland soils under future high temperatures. The team found that the peatland’s soil microbial communities allocated more carbon to enzyme production in search of phosphorus as temperatures climbed. This diversion of carbon resources could reduce future carbon losses by microbial respiration from the peatland.
As boreal peatlands face warmer and drier conditions, it is expected that more carbon will be lost from these carbon-rich soils through increased microbial activity. This study showed that enhanced respiration and concomitant loss of carbon is potentially constrained by nutrient demands of the microorganisms. This tradeoff may help the peatland ecosystem retain soil carbon as temperatures warm.
Root exudates are carbon compounds, such as sugars and organic acids, which are easily consumed by soil microorganisms. With a warming climate, science suggests that increased photosynthesis by plants could lead to more photosynthate released as root exudates to the soil microbial community. To examine this question, researchers used laboratory incubations to control both temperature and moisture and simulate belowground substrate additions under an accelerated growing season. Results showed that with a moderate increase in temperature, the addition of common root exude compounds in peatlands initially increased carbon lost through microbial respiration above those treatments receiving water only. However, when pushed to future expected high temperatures, additional exudate compounds dampened the amount of additional carbon respired as compared to treatments receiving water only. This reduction in respiration suggests the microorganisms allocated carbon compounds to enzyme production to mine for limited resources instead of respiring carbon. The data also support the idea that boreal peatland microbial communities maintain a more narrow range in function, measured as respiration, across a range in climate conditions. A wide climatic niche in addition to reallocation of carbon resources dampens the magnitude of change in carbon respiration with increasing temperatures.
Biological and Environmental Scienes Directorate
This material is based upon work supported by the US Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science (TES) Program, under grant ER65430 to Iowa State University.
A New Role for Microbes in Peatland Nitrogen Supply
Research reveals that bacteria contribute to peatland nitrogen availability through organic nitrogen breakdown.
Nitrogen is a critical nutrient regulating productivity in many ecosystems and influences nutrient availability by affecting organic matter decomposition rates. Nitrogen fixation—converting atmospheric nitrogen into biologically available compounds—by microorganisms has historically been considered the primary nitrogen source in peatlands. However, recent work shows that nitrogen fixation alone cannot meet nitrogen requirements. Researchers at Pacific Northwest National Laboratory and Iowa State University evaluated the genetic potential of microorganisms to supply nitrogen in peatlands via the breakdown of large organic molecules. Results show bacterial potential for cleaving amino acids from organic inputs from plants. This finding contrasts with the paradigm that fungi are genetically superior in their capacity to release nitrogen from organic molecules.
Understanding the processes that govern carbon and nutrient dynamics in northern peatlands is critical to predicting future biogeochemical cycles. These ecosystems account for 15‒30% of global soil carbon storage. This study expands the understanding of coupled carbon and nitrogen cycles in northern peatlands, with results indicating that understudied bacterial and archaeal lineages may be central in these ecosystems’ response to environmental change. This project leverages DOE’s one-of-a-kind SPRUCE infrastructure to address mechanisms underlying ecosystem responses to climate change and contribute to the broader goals of the Terrestrial Ecosystem Science Scientific Focus Area.
Nitrogen is a common limitation in plant productivity and its source remains unresolved in northern peatlands, which are vulnerable to environmental change. Decomposition of complex organic matter into free amino acids has been proposed as an important nitrogen source, but the genetic potential of microorganisms catalyzing this process has not been examined.
Researchers evaluated the microbial—fungal, bacterial, and archaeal—genetic potential for organic nitrogen break down in peatlands at Marcell Experimental Forest in northern Minnesota. The team investigated the abundance and diversity of protease genes involved in the release of nitrogen from organic matter across depths and in two distinct peatland environments—bogs and fens. Analysis of shotgun metagenomic data demonstrates high genetic potential for production of free amino acids across a diverse range of microbial guilds.
Researchers also found a high abundance of protease genes compared with nitrogen-fixation genes typically thought to provide nitrogen in peatlands. Bacterial genes encoding proteolytic activity suggested a predominant role for bacteria in regulating productivity, which contrasted with the paradigm of fungal dominance of organic nitrogen decomposition. This research is foundational to understanding the mechanisms by which carbon cycling is linked to ecosystem nutrient status in the face of changing climate.
This research is supported by the U.S. Department of Energy Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science SFA.
A Slippery Slope: Soil Carbon Destabilization
Carbon gain or loss depends on the balance between competing biological, chemical, and physical reactions
Despite a breadth of research on carbon accrual and persistence in soils, scientist lack a strong, general understanding of the mechanisms through which soil organic carbon (SOC) is destabilized in soils. In a new review article, researchers synthesized principles of soil chemistry, physics, and biology to explain carbon loss in soils. They found that destabilization does not equal stabilization in reverse. Rather, carbon gain or loss depends on the balance between competing biological, chemical, and physical reactions that can be altered by changes in weather and temperature.
Rates of soil carbon respiration are increasing with current changes in climate and land use. Therefore, understanding destabilization processes in the soil carbon cycle is imperative. This review informs a more robust understanding of the processes that result in carbon loss and feedbacks to the Earth system. With this context, empirical and computational scientists can target better questions about the potential for soils to affect climate through the carbon cycle, which is important for improving predictive biogeochemical and climate models.
Most empirical and modeling research on soil carbon dynamics focus on processes that control and promote carbon stabilization. However, the mechanisms through which soil organic carbon (SOC) is destabilized in soils may be even more important to understand. Destabilization processes occur as SOC shifts from a “protected” or passive state, to an “available” or active state. In the available state, microbes can transform soil carbon to gaseous or soluble forms that are then lost from the soil.
The reviewers, from Pacific Northwest National Laboratory, Dartmouth College, and Oregon State University, considered two well-known phenomena—soil carbon priming and the Birch effect—to show how different mechanisms interact to increase carbon losses. They categorized carbon destabilization processes into three general categories: (1) release from physical occlusion through processes such as tillage, bioturbation, or freeze-thaw and wetting-drying cycles; (2) carbon desorption from soil solids and colloids; and (3) increased carbon metabolism by microbes.
By considering the different physical, chemical, and biological controls as processes that contribute to SOC destabilization, researchers can develop new hypotheses about the persistence and vulnerability of carbon in soils and make more accurate and robust predictions of soil carbon cycling in a changing environment.
Pacific Northwest National Laboratory
V.L. Bailey was supported by the U.S. Department of Energy, Office of Science, Biological and Environmental Research as part of the Terrestrial Ecosystem Sciences Program. The Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute under contract DE-AC05-557 76RL01830. K. Lajtha was supported by NSF DEB-1257032.
STAR Workshop: Terrestrial-Aquatic Research in Coastal Systems
From September 24–26, 2018, Pacific Northwest National Laboratory hosted a System for Terrestrial–Aquatic Research (STAR) workshop to discuss terrestrial–aquatic interface (TAI) research needs. The purpose of this workshop was to continue discussion initiated at the 2016 Department of Energy (DOE)-Biological and Environmental Research (BER) workshop: Research Priorities to Incorporate Terrestrial–Aquatic Interfaces in Earth System Models. Specifically, this workshop focused on terrestrial–aquatic interfaces near the coastline, which have been identified as a major gap in Earth system models (ESMs) and observational networks, important ecosystems that are vulnerable to disturbances from both the land and sea, as well as hubs for human habitation and commerce.
STAR Workshop Report
PNNL – Pacific Northwest National Laboratory. 2019. STAR Workshop: Terrestrial-Aquatic Research in Coastal Systems. PNNL-28611, Pacific Northwest National Laboratory, Richland, Washington.