Sarah Placella

Sarah Placella

AgreenSkills session, year: 1st session, 2013

Receiving laboratory: Eco&Sol Functional Ecology & Soil Biogeochemistry Montpellier, France

Country of origin : USA




Mobility project

Understanding the influence of biopores on microbial function and activity

Soil microorganisms regulate the major biogeochemical cycles (Carbon, Nitrogen,

and Phosphorus) and thereby nutrient availability to plants and greenhouse gas fluxes to the atmosphere. Water availability, oxygen, and carbon availability are among the best known drivers of microbial activity and function. Biopores such as plant root channels and earthworm burrows are like superhighways for these key factors, featuring much greater fluxes of water, oxygen, and nutrients including carbon compared to bulk soils. The result is that to a microorganism, earthworms and plants are ecosystem engineers, altering soil structure, nutrient inputs, and water dynamics. Our aim is to understand the role these organisms play in shaping microbial communities and their functional capacities; our research investigates this by mapping the spatial heterogeneity of the rhizosphere (plant roots) and drilosphere (earthworm burrows and casts) in terms of soil properties and enzyme activities as well as microbial communities. We are focusing on amylase, protease, and acid phosphatase activities for their importance to C, N, and P cycling, respectively; we are combining these in situ measures with near and mid infra-red spectrographic maps, also in situ and non-destructive, that provide data on the types and quantities of C, N, and P in the soil. Finally, at the end of the biweekly-sampled experiment, we will destructively sample key regions, such as root tips, nodules, bulk soil, and earthworm channels, noting the cartography as well as the current and past influences. These samples will be used to measure soil properties by HPIC and the quantities of key functional genes involved in C, N, and P cycling. By combining geostatistics and multivariate statistics, we will understand where biogeochemical hotspots are in soils with respect to plants and earthworms as well as gain insights into how long the soil remains influenced by these engineers.

Biography & research interests

My research links the activity of microorganisms in their natural environments to the ecosystem fluxes they mediate. I am especially interested in the causes of temporal and spatial heterogeneity in microbial processes and their implications for biogeochemistry and ecosystem fluxes. My PhD, done at UC Berkeley under the direction of Mary Firestone, was focused on natural microbial awakening following wet-up, the first rainfall following the hot, dry summer occurring annually in California grasslands. As a postdoctoral research fellow, I worked at Michigan State University looking at the impacts of drought on microbial community structure and respiration. Currently, as a postdoctoral fellow at INRA in Montpellier with Eco&Sols, under the supervision of Philippe Hinsinger, I am studying the impacts of ecosystem engineers, specifically plants and earthworms, on soil heterogeneity, microbial communities, and nutrient (C, N, and P) cycling.

Selected publications

Placella SA, Firestone MK (2013). Transcriptional response of nitrifying communities to soil wet-up, Applied and Environmental Microbiology79: 3294-3302.

Sudderth EA, St Clair SB, Placella SA, Swarbreck SM, Castanha C, Herman DJ, Fischer ML, Kleber M, Sudderth EB, Torn MS, Firestone MK, Andersen GL, Ackerly DD (2012). Sensitivity of resource pools and fluxes to dry periods under low and high rain treatments on two contrasting soils. Ecosphere 3: Article 70.

Placella SA, Brodie EL, Firestone MK (2012). Rainfall-induced carbon dioxide pulses result from sequential resuscitation of phylogenetically clustered microbial groups. Proceedings of the National Academy of Sciences USA 109: 10931-10936.

Leakey ADB, Ainsworth EA, Bernard SM, Markelz RJC, Ort DR,Placella SA, Rogers A, Smith MD, Sudderth EA, Weston DJ, Wullschleger SD, Yuan S (2009). Gene expression profiling: opening the black box of plant ecosystem responses to global change. Global Change Biology 15: 1201-1213.

Szlavecz K, Placella SA, Pouyat RV, Groffman PM, Csuzdi C, Yesilonis I (2006). Invasive earthworm species and nitrogen cycling in remnant forest patches. Applied Soil Ecology 32: 54-62.




CV: Download curriculum vitae