F. RESEARCH F.1 Research statement

Erika Marín-Spiotta 1 of 3

F. RESEARCH

F.1 Research statement

Earth system models vary widely in their predictions of carbon (C) uptake and release by the

biosphere, partly due to great uncertainties in the response of soils, one of the largest C reservoirs

in the surface earth system. The world’s soils play a major role in the exchange of greenhouse

gases with the atmosphere, in sustaining primary production, and in providing food security.

Despite this, the sensitivity of soils to current and historic changes in climate and land use

remains highly uncertain. My research draws from biogeochemistry, ecology, soil science, and

biogeography to advance our knowledge of environmental and anthropogenic factors regulating

terrestrial C storage. My questions cross spatial and temporal scales – from microscopic to

regional and annual to millennial. My approach encompasses conceptual, synthetic and

experimental research, fieldwork, and laboratory measurements. Below I highlight selected

contributions under three themes. I use the plural we to indicate work with my students.

Hierarchical controls on carbon turnover within and across ecosystem boundaries

Improving estimates of feedbacks between the biosphere and the climate system requires

enhanced understanding of mechanistic controls on C turnover. My research applies multiple

approaches, including isotopic and spectroscopic data, to measure molecular and environmental

factors regulating biogeochemical processes to inform predictions of future change.

The residence time and retention of C in soils is strongly influenced by soil properties, e.g.,

mineralogy and structure, which are not well represented in biogeochemical models coupled to

land and climate models. Most knowledge of soil C comes from temperate regions, despite the

major role of tropical soils in the global C cycle. Even in the tropics, available data are not

representative [1] and our research shows mechanisms differ in highly weathered soils [e.g., 2].

With NSF CAREER funding, I am investigating hierarchical controls on C turnover in a

diversity of tropical soils to improve understanding of C dynamics. This work will produce one

of the largest databases for tropical radiocarbon data to better constrain estimates of soil C age.

Soils are the dominant contributors of C to inland and coastal water bodies, influencing aquatic

productivity and greenhouse gas production. Despite this, terrestrial and aquatic research

communities often work in isolation of each other. I led an interdisciplinary effort to reveal how

emerging conceptual models in soil organic matter (OM) research can resolve long-standing

paradoxes surrounding the fate of land-derived C in marine systems [3]. We proposed that

predictions of the reactivity of OM should be reassessed given: 1) a shift away from an emphasis

on chemical recalcitrance as a primary predictor of turnover, 2) new interpretations of

radiocarbon ages, 3) and the recognition that most dissolved OM leaving soils has been

microbially processed. Drawing from this work and my research on the hydrologic transport of

C in soils [4], I plan to investigate terrestrial-aquatic C fluxes with the North Temperate Lakes

Long-Term Ecological Research (NTL-LTER) group.

Legacies of past climate and landscape disturbances on terrestrial carbon storage

Improved mechanistic understanding of OM storage during past periods of environmental

change can help predict the vulnerability of terrestrial C to current and future trends. My research

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has focused on the response of soil C to climatic and anthropogenic transformations of the

landscape.

In a novel approach that combined biogeochemistry with geomorphology, we found that

landscape disturbance during a period of rapid climatic change contributed to the persistence of

ancient C in a deeply buried paleosol [5]. This research, which was published in Nature

Geoscience and received international press coverage, revealed that buried soils are a grossly

underestimated reservoir of C that could become a C source if reconnected to the atmosphere

through erosion or other disturbances. In a new synthesis of existing data on buried soil C

globally, we proposed that depositional processes play an underappreciated role in the

accumulation and storage of organic C at depth [6], contributing a new perspective on the source

of deep soil C. Future work will examine the vulnerability of buried C to environmental change

to assess the potential risk of C release to the atmosphere.

Pedogenic factors can influence the sensitivity of soils to disturbance. In one of the few studies

of land use effects on landscape-scale variability in arid soils, we found differences in soil C and

nitrogen across different parent materials within the same soil order [7]. This work highlights the

importance of assessing interactions between geologic and human factors in regional C

inventories and of identifying mechanisms influencing the response of soils to land use.

With funding from the USDA and my NSF CAREER award, I have initiated research to quantify

soil C under different land cover types. This project is part of a national effort to improve

baseline data for climate and land use projections and better understand the effects of historical

land use on current C stocks. Despite the known importance of former land-use legacies on soil

C cycling, most regional and global soil C mapping efforts lack any consideration of site history.

Interactions between biodiversity and biogeochemistry in human-dominated ecosystems

Human modifications of the landscape alter species composition, with consequences for

biogeochemical cycling and conservation. My research addresses interactions between changing

plant and microbial diversity and ecosystem processes through experimental manipulations and

historical changes in land cover.

The transformation of agriculture for bioenergy crop production has implications for the

environmental sustainability of biofuels. In a collaborative project funded by the USDA, we

found positive relationships among plant diversity, microbial communities, and soil C

accumulation [8]. With support from the Great Lakes Bioenergy Research Center and the

Radiocarbon Collaborative, we are examining how crop type affects soil OM pools and the age

of microbially-respired C across soils of contrasting texture. This work contributes to theory on

how diversity affects ecosystem function and to evaluating the full effects of land use conversion

for bioenergy.

Human use can launch sites on new trajectories, with unpredictable consequences for above- and

belowground ecological interactions and the provision of ecosystem services. Our NSF-funded

research has found strong plant-driven successional controls on microbial ecology in post-

agricultural forests [2, 9]. Changes in plant communities influence soil nitrogen and biomass C

accumulation [10, 11], affecting ecosystem C sequestration potential. Building upon my work on

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reforestation effects on soil C [1, 12, 13], ongoing research in my lab will close some of the gaps

in knowledge of how land-use legacies alter forest recovery in Earth system models.

References Cited (underlined names are student co-authors)

1. Marín-Spiotta, E. and S. Sharma. 2013. Carbon storage in successional and plantation

forest soils: a tropical analysis. Global Ecology and Biogeography 22: 105-117.

2. Smith, A.P., E. Marín-Spiotta, M.A. De Graaf, and T. Balser. 2014. Microbial

community structure varies across soil organic matter pools during tropical land cover

change. Soil Biology and Biochemistry 77: 292-303.

3. Marín-Spiotta, E., K.E. Gruley, J. Crawford, E.A. Atkinson, J.R. Miesel, S. Greene, C.

Cardona-Correa, and R.G.M. Spencer. 2014.

Paradigm shifts in soil organic matter

research affect aquatic carbon turnover interpretations: Transcending disciplinary and

ecosystem boundaries. Biogeochemistry 117: 279-297. doi: 10.1007/s10533-013-9949-7

4. Marín-Spiotta, E., O. A. Chadwick, M. Kramer, and M. S. Carbone. 2011. Carbon

delivery to deep mineral horizons in Hawaiian rain forest soils. Journal of Geophysical

Research: Biogeosciences 116, G03011, doi:10.1029/2010JG001587.

5. Marín-Spiotta, E., N.T. Chaopricha, A. F. Plante, A.F. Diefendorf, C.W. Müller, S.

Grandy, and J.A. Mason. 2014. Long-term stabilization of deep soil carbon by fire and

burial during early Holocene climate change. Nature Geoscience 7: 428-432. doi:

10.1038/NGEO2169

6. Chaopricha, N.T. and E. Marín-Spiotta. 2014. Soil burial contributes to deep soil organic

carbon storage. Soil Biology and Biochemistry 69: 251-264.

7. Mayes, M., E. Marín-Spiotta, L. Szymanski, A. Erdogan, M. Ozdogan and M. Clayton.

2014. Soil type mediates effects of land use on soil carbon and nitrogen in the Konya

Basin, Turkey. Geoderma 232-234: 517-527.

8. Tiemann, L.K., A.S. Grandy, E.E. Atkinson, E. Marin-Spiotta and M.D. McDaniel. Plant

biodiversity enhances belowground communities and functions in an agroecosystem. (In

revision for Ecology Letters)

9. Smith, A.P., E. Marín-Spiotta, and T. Balser. Seasonal and successional changes in soil

microbial community structure during reforestation of a tropical post-agricultural

landscape. (In review at Global Change Biology)

10. Marín-Spiotta, E., R. Ostertag, and W.L. Silver. 2007. Long-term patterns in tropical

reforestation: plant community composition and aboveground biomass accumulation.

Ecological Applications 17:828-839. doi: 10.1890/06-1268

11. Atkinson, E.E. and E. Marín-Spiotta. Land use legacy effects on structure and

composition of subtropical dry forests in St. Croix, U.S. Virgin Islands. Forest Ecology

and Managament. Accepted.

12. Marín-Spiotta, E., W.L. Silver, C.W. Swanston, and R. Ostertag. 2009. Soil organic

matter dynamics during 80 years of reforestation of tropical pastures. Global Change

Biology 15: 1365-1614. doi: 10.1111/j.1365-2486.2008.01805.x

13. Marín-Spiotta, E., C.W. Swanston, M.S. Torn, W.L. Silver, and S.D. Burton. 2008.

Chemical and mineral control of soil carbon turnover in abandoned tropical pastures.

Geoderma 143:49-62. doi:10.1016/j.geoderma.2007.10.001