Root-Mediated Impacts of Plant Volatile Organic Compound Emissions on Soil Carbon
Authors:
Qunli Shen1,2* ([email protected]), Kolby Jardine2, Annie DiGuiseppe2, Zhaoxin Zhang1, Margaret Torn2, Romy Chakraborty2, Eoin Brodie2, Laura K. Meredith1
Institutions:
1University of Arizona; 2Lawrence Berkeley National Laboratory
Goals
The overarching project goal is to verify and quantify volatile organic compounds (VOCs) as direct and indirect contributors to soil carbon (C) stabilization within the rhizosphere and beyond through teleconnections, and to determine their underpinning ecological and metabolic mechanisms. The long-term motivation for this project is to transform the current conceptual understanding and predictive capacity of microbial systems and soil C stabilization to include the important roles of volatile compounds. This presentation falls under the group’s objective to determine the contributions of root-released VOCs and VOC transformations by soil microbiomes to soil C cycling and stabilization. Specifically, in these tasks, researchers quantify subsurface root and soil VOC cycling to determine how deep soil warming influences soil C in a coniferous forest and how plant productivity, root biomass, and plant growth stages influence soil C in an agroecosystem.
Abstract
Plants are recognized as the dominant source of biogenic VOCs to the atmosphere, where they play critical roles in air quality and climate, yet the parallel impact of plant-derived VOCs on the pedosphere (soil) remains poorly quantified. VOCs released by decomposing litter can contribute to soil C pools including those associated with soil C stabilization, and researchers hypothesize that root VOCs can also contribute to these soil C pools. Furthermore, researchers anticipate this pathway for soil C stabilization will depend on plant physiological traits (e.g., photosynthesis, growth rates, stomatal conductance), rhizosphere microbes and their activity, and soil environmental factors. Currently, rhizosphere VOC cycling remains poorly described, in part due to a lack of developed methods. In this project, the group integrated new in situ and non-destructive approaches for measuring root VOCs and tracking their fate in soil.
The group designed two separate rhizobox systems to measure VOCs from soil and rhizosphere from Ponderosa pine seedlings and soil from the temperate coniferous Blodgett Experimental Forest in the Sierra Foothills in California. Both systems passively collected soil gas using diffusive teflon samplers shaped either as a cylindrical soil gas probe, as researchers have described previously (Roscioli et al. 2021; Gil-Loaiza et al. 2022), or a diffusive sheet connected to a large artificial macropore. Subsurface VOCs and carbon dioxide (CO2) in soil (soil only) or rhizosphere (soil and plant) treatments were measured using a suite of online gas analyzers including a PTR-MS, TD-GC-MS, and CRDS over a 6-day period with a diurnal light and temperature program (light 6:00–20:00, 6:00: 15℃, 14:00: 35℃). Alongside higher levels of CO2 (rhizosphere respiration), the group found elevated soil gas concentrations of methanol, acetic acid, acetone, and acetaldehyde in the pine tree rhizosphere compared to soil alone, indicating a root source. Soil appears to have been a source of 1,2-butadiene and isoprene (fragment) that were elevated in both treatments. These results are consistent with the previous discovery of high concentrations of volatile compounds including methanol at Blodgett (nuclear magnetic resonance on soil extracts), suggesting that pine roots may be an important source of these compounds and that the rhizobox systems are a useful tool for capturing and partitioning VOC sources and sinks in the rhizosphere. Ongoing research is comparing the performance of the two rhizobox systems and performing experiments to evaluate the impact of soil warming and moisture availability on root and soil VOC cycling and their contributions to soil carbon under controlled conditions. These results will be compared to those from the group’s upcoming field campaign at the deep soil warming experiment in the Blodgett Research Forest.
References
Gil-Loaiza, J., et al. 2022. “Versatile Soil Gas Concentration and Isotope Monitoring: Optimization and Integration of Novel Soil Gas Probes with Online Trace Gas Detection,” Biogeosciences 19(1). DOI:10.5194/bg-19-165-2022.
Roscioli, J. R., et al. 2021. “Soil Gas Probes for Monitoring Trace Gas Messengers of Microbial Activity,” Scientific Reports 11(1). DOI:10.1038/s41598-021-86930-8.
Funding Information
This material is based upon work supported by the DOE Office of Science, BER program, GSP under contract number DE- SC0023189 to the University of Arizona. This work was performed at Lawrence Berkeley National Laboratory supported by the U.S. DOE, Office of Science, BER program, GSP, and in-kind support from the Environmental System Sciences programs under contract number DE-AC02-05CH11231.