B101-11
Microbial respiration and temperature effects shape the in situ belowground CO2 efflux of the root-soil microbiome of 8 temperate hardwood tree species.

Tuesday, 15 December 2020: 10:40
Virtual
James Aaron Hogan1, Jessy L. Labbe2, Jennifer Franklin3, Kevin P. Hoyt4, Oscar J. Valverde-Barrantes5, Chris Baraloto1 and Jeff Warren6, (1)Florida International University, Department of Biological Sciences, Miami, FL, United States, (2)Oak Ridge National Lab, Bioscience Division, Oak Ridge, TN, United States, (3)University of Tennessee, Department of Forestry, Wildlife & Fisheries, Knoxville, TN, United States, (4)UT Forest Resources AgResearch and Education Center, Oak Ridge, United States, (5)Florida International University, Department of Biological Sciences, Miami, United States, (6)Oak Ridge National Laboratory, Environmental Sciences Division and Climate Change Science Institute, Oak Ridge, TN, United States
Recorded Presentation
Abstract:
Context/Purpose: Understanding the factors that control soil CO2 efflux in forests is a key component for global climate cycle modeling. CO2 efflux from the soil is derived from root and microbial respiration, which is highly dynamic and depends on edaphic and environmental conditions, as well as root traits and microbial community composition.

Methods: In June, 2019, in-situ root trays housing entire root systems and their surrounding soil were installed on 8 temperate tree species that varied in their root functional strategies and mycorrhizal type. In a paired design, half of the trays were repeatedly treated with bactericide/fungicide (ZeroTol) to suppresses microbial and fungal levels. Soil CO2 efflux was measured repeatedly for nearly one year using a custom chamber gas exchange system, with concurrent measurements of soil moisture and temperature. We also measured respiration rates and morphological traits of excised root systems. Microbial carbon (C) and nitrogen (N) were measured on soils at the end of the experiment using chloroform fumigation to quantify soil microbial biomass.

Results: Contrary to our prediction, the application of the ZeroTol slightly increased rates of CO2, but did lead to a 69% average reduction in microbial N, with no change in microbial C. Rates of soil CO2 efflux ranged from 0.3 to 12 µmols m^-2 sec^-1, being slightly higher for arbuscular mycorrhizal trees than for ectomycorrhizal trees. Rates increased with increasing temperature due to seasonality but were unrelated to soil moisture. Rates of root root tissue respiration ranged from <0.1 to 0.7 µmols g-1 sec-1, varied among species, and were negatively correlated to root length and tissue density.

Conclusion: Rates of belowground CO2 efflux were very similar among species. Additionally, there was minimal variation among rates of root tissue respiration. Variation in the microbial composition and metabolic activity within the rhizosphere microbiome of trees likely accounts for differences in belowground CO2 efflux, as evidenced by the effect of soil temperature. We conclude that at the sampling unit of a single root system and its surrounding soil, rates of tissue respiration constitute a small fraction of total belowground CO2 efflux, and that separating root-based respiration from microbial respiration remains challenging.

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