RESEARCH | Emilylacroix

CURRENT TOPICS (POSTDOCTORAL WORK @ UNIL)

Are roots key drivers of anoxic microsites in upland soils?

For decades, biogeochemists have speculated that roots are key drivers of anoxic microsites – anomalous volumes of oxygen depletion – in upland soils. Rhizosphere-associated anoxic microsites are hypothesized to regulate plant contaminant uptake, nutrient availability, and the fate of root-derived carbon. However, despite the potential importance of rhizosphere-associated anoxic microsites, it remains unclear why, when, and where anoxic microsites form in the rhizosphere. For my postdoc, we used two technical approaches to investigate oxygen dynamics in the rhizosphere.

Microfluidics

We pair planar optical oxygen sensors with microfluidic devices mimicking a soil structure to map the distribution of oxygen in a young wheat rhizosphere. Next, we hope to determine whether the anoxic microsites we observed stimulate anaerobic microbial activity in our "soil".

Reverse microdialysis

We use reverse microdialysis à-la-Konig-et-al-2022 to simulate root exudation in soils of different textures. We then use planar optical oxygen sensors and 13C labelling to quantify the extent of oxygen depletion in the "rhizosphere" and determine the fate of root-derived C in these model systems.

FUTURE TOPICS (The Lacroix Lab @ Dartmouth)

Roots & Minerals

What is the fate of mineral-associated carbon, nutrients, and contaminants in the rhizosphere?

Roots perform several natural processes that help the plant grow. These processes create chemical gradients around plant roots. Separately, we know that changes in chemical environments can facilitate mineral dissolution/transformations as well as sorption/desorption reactions. However, the cascading effects between plant stressors, root processes, and mineral surface processes are still ill-defined. In this research theme, we use laboratory and greenhouse systems to:

better understand mineral processes in the rhizosphere and
predict how large scale human-disturbances (e.g., climate change, agriculture) ultimately influence these mineral surface processes and nutrient and contaminant mobility

Anoxic Microsites

How will anoxic microsites in New England watersheds respond to climate change?
How will this affect greenhouse gas emissions and nutrient and contaminant mobilization?

Anoxic microsites are non-majority soil volumes in which oxygen demand is faster than oxygen supply. As a result, you end up with a pocket of soil that is without oxygen in a soil that is otherwise oxic. It remains unknown how anoxic microsites vary over space and time in different types of soil and their effects on various biogeochemical cycles (e.g., C, N, Fe). In this research theme, we use a combination of field and laboratory work to:

evaluate the distribution, lifetime, and (redox) gradient magnitude anoxic microsites across various soils
determine how anoxic microsites will respond to warmer and wetter conditions in New England
quantify the influence of anoxic microsites on soil C cycling (among other elemental cycles)

Image from Lacroix et al. 2023. ACS Earth & Space Chem.

Soil Carbon Stabilization in Managed Ecosytems

What is the relative importance of various soil carbon protection mechanisms?
Can we use this knowledge to help soils store more carbon?

vs.

MINERAL PROTECTION

PHYSICAL PROTECTION

RESOURCE
LIMITATIONS

The size of the soil organic carbon (C) stock is determined by a balance of inputs (i.e., photosynthesis) and outputs (i.e., microbial respiration). Soil C protecion mechanisms are the processes by which microbes are slowed down or inhibited from turning soil C into carbon dioxide. In each ecosystems, multiple soil C protection mechanisms work together to partially determine soil organic C content. However, the relative importance of soil C protection mechanisms, how they interact, and their susceptibility to disturbance across ecosystems is still being studied. In our group, we will use a mix of field and laboratory analyses to:

develop a mechanistic understanding of soil C protection within agricultural systems and
investigate how specific management practices and soil properties modulate these processes

PUBLICATIONS

For the most accurate and up-to-date publication list, see my Google Scholar or ORCID profile.

Lacroix, E.M.; Gomes, A.; Barratt Heitmann, G.; Schuler, D.; Dekas, A.; Liptzin, D.; Aberle, E.; Watts, D.B.; Nelson, K.A.; Culman, S.; Fendorf, S. 2024. Microbial proxies for anoxic microsites vary with management and partially explain soil carbon concentration. Environmental Science & Technology. 58: 11459-11469.

Noël, V.; Boye, K.; Naughton, H.; Lacroix, E.M.; Aeppli, M.; Kumar, N.; Fendorf, S.; Webb, S. 2024. X-ray chemical imaging for assessing redox microsites within soils and sediments. Frontiers in Environmental Chemistry. 5:1329887.

Lacroix, E.M.; Aeppli, M; Boye, K.; Brodie, E.; Fendorf, S.; Keiluweit, M.; Naughton, H.R.; Noël, V.; Sihi, D. 2023. Consider the anoxic microsite: acknowledging and appreciating spatiotemporal redox heterogeneity in soils and sediments. ACS Earth & Space Chemistry. 7: 1592 – 1609.

Lacroix, E.M.; Mendillo, M.; Gomes, A.; Fendorf, S. 2022. Contributions of anoxic microsites to soil carbon protection across soil textures. Geoderma. 425: 116050.

Lacroix, E.M.; Masue-Slowey, Y.; Dlott, G.; Keiluweit, M.; Chadwick, O.; Fendorf, S. 2022. Mineral Protection and Resource Limitations Combine to Explain Profile‐Scale Soil Carbon Persistence. JGR Biogeosciences. 127 (4): 1-14.

Aeppli, M.; Babey, T.; Engel, M.; Lacroix, E.M.; Tolar, B.; Fendorf, S.; Bargar, J.; Boye, K. 2022. Export of organic carbon from reduced fine-grained zones governs biogeochemical reactivity in simulated aquifer. Environmental Science & Technology. 56 (4): 2738-2746.

Lacroix, E.M.; Rossi, R.J.; Fendorf, S.; Bossio, D. 2021. Effects of moisture and physical disturbance on pore-scale oxygen content and anaerobic metabolisms in upland soils. Science of the Total Environment. 780: 146572.

Lacroix, E.M.; Petrenko, C.L.; Friedland, A.J. 2016. Evidence for Losses from Strongly Bound SOM Pools After Clear Cutting in a Northern Hardwood Forest. Soil Science. 181(5): 202-207.

Petrenko, C.L.; Bradley-Cook, J.; Lacroix, E.M.; Friedland, A.J.; Virginia, R.A. 2016. Comparison of carbon and nitrogen storage in mineral soils of graminoid and shrub tundra sites, Western Greenland. Arctic Science. 2(4): 165-182.