Why is Arctic tundra soil respiration carbon limited at low temperatures?
EMSL Project ID
51407
Abstract
Soil microbial communities are active during much of the long Arctic winter, despite low temperatures, so overwinter microbial activity is important to global carbon (C) budgets. C-rich Arctic soils are warming more in winter than summer, and warming at low temperatures has disproportionately large effects on respiration rates. Temperature is considered the overriding control on overwinter soil microbial activity. However, our results demonstrate that persistently warm organic tundra soils in winter can lead to starvation of the microbial community for accessible C, despite high total C. Thus, winter respiration cannot be predicted from soil temperature alone. Our goal is to develop a predictive understanding of the biochemical mechanisms controlling the temperature responses of soil respiration in Arctic tundra, particularly the interactions between respiration, enzyme activities, and substrate availability to the microbial community as a function of temperature. We propose to answer the questions: when and why is microbial activity in organic tundra soils C limited at low temperatures (-10 to 10 deg. C), and how do responses change with freezing? To answer these questions, we will incubate organic tundra soils under different conditions and temperatures and measure respiration, activities of the enzymes catalyzing different steps of lignocellulose degradation and concentrations of their reaction products, as well as other soluble C forms and microbial metabolites that might fuel and/or reflect microbial activity. With this information we will characterize microbial substrate availability, catalysis, and consumption as a function of temperature. We will use the results to develop mechanistic model predictions of in situ respiration using field soil temperatures monitored at our sites in NW Alaska. Access to EMSL is critical for this research because advanced analytical capabilities (FTICR, NMR, GC-MS, LC-MS) are required to measure changes in microbial C substrates, individual enzyme substrates and reaction products as functions of temperature. This research closely fits PNNL's Environmental Transformations and Interactions Area's focus on understanding hydrobiogeochemical processes governing terrestrial carbon (C) and nutrient cycling, including microbial processes that drive nutrient cycling, and plant-microbe-soil-atmosphere interactions. We will characterize the decomposition dynamics and molecular chemistry of Arctic tundra soil organic matter and investigate the mechanisms and processes that influence microbial access to C substrates under climate change. This study will also address the Functional and Systems Biology Area's focus on integrated modeling and structural biology studies of the enzymatic systems in biomass deconstruction, as well as experimental and modeling approaches in biological systems (e.g., bacteria, fungi) to enable predictive understanding of C and nutrient flux. This work will enhance the molecular-scale understanding and mathematical modelling of the fundamental controls on decomposition, especially at low temperatures common in arctic and boreal biomes, which contain the largest soil C pools vulnerable to warming, and are relevant to the DOE's research in boreal (SPRUCE) and Arctic (NGEE) systems.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2020-10-01
End Date
2023-06-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members