Past Research

Vulnerability of carbon in buried soils to climate change and landscape disturbance


Student: Laura Szymanski, PhD 2021

This project will test the potential for deep buried soil organic matter to become a carbon source in response to changes in climate or land use that affect the connectivity of buried soils to the atmosphere. The research aims to understand (1) how soil burial contributes to the persistence of carbon in the form of soil organic matter and (2) whether exposure to surface conditions can trigger the decomposition of ancient carbon. The proposed study site is located in the U.S. Great Plains, where climate-driven loess deposition during the late Pleistocene and Holocene resulted in sequences of buried soils in thick loess deposits. The vulnerability of ancient organic matter to changing environmental conditions will be measured in two ways. First, changes in organic matter age, composition and bioavailability will be quantified along eroding and depositional field toposequences, where the paleosol exists at varying degrees of isolation from the modern landscape surface. Second, laboratory manipulations will measure the effects of carbon substrates, nitrogen availability, and microbial composition on ancient organic matter decomposition and mobilization in gaseous and dissolved forms. This study combines a geomorphic approach drawing from paleoclimatic reconstructions with advanced geochemical, spectroscopic and metagenomic techniques to generate new knowledge on environmental controls on carbon biogeochemistry. Funded by NSF Geobiology and Low Temperature Geochemistry. Collaborators: Dr. Joe Mason, Dr. Asmeret Berhe and Dr. Marie-Anne de Graaff.

Environmental controls on soil carbon storage and turnover in the Caribbean


Student: Elliot Vaughan, PhD 2020

The primary research objectives of this project are to: 1)  Quantify soil carbon under different land uses across environmental gradients in Puerto Rico to determine the role of land use and state factors on soil C storage, 2) Evaluate the magnitude and persistence of legacy effects of historical land use on soil carbon with time since conversion across different soil types, and 3) Determine the effect of soil type, climate and land use on the relative importance of different physical, chemical and biological processes contributing to carbon sequestration in tropical soils. In collaboration with the USDA NRCS Rapid Carbon Assessment and funded by NSF CAREER award. Collaborators: Carmen Santiago, Manuel Matos, Samuel Rios. Read more about this project here.

Forest succession effects on roots and soil fungi across different soil orders in tropical ecosystems


Student: Emily J. Diaz Vallejo, MS 2020

The objective of this project is to evaluate how land use legacies affect plant roots and soil fungi through forest succession and to understand how these biotic components can influence soil organic matter dynamics across different soil orders in tropical ecosystems. We are particularly interested in measuring the plasticity of root and fungal traits and their role in carbon, nitrogen, and phosphorus dynamics. Through evaluating soil biotic components across forest succession at different soil orders, we will better understand how human disturbances across different environment impact soil organic matter dynamics. This work will provide empirical data for global carbon models to have better estimates of carbon dynamics. Understanding biotic responses to forest recovery can have implications for improving land management, ecosystem productivity, and our ability to predict feedbacks between tropical ecosystems and future disturbances.

Soil resource heterogeneity and tree species diversity in tropical secondary forests

DSCN3174PhD Student: Ricardo Rivera

The objective of this research is to measure the heterogeneity of soil nutrient pools and availability through successional stages in post-agricultural forests. Characterizing these spatial patterns through succession will elucidate the importance of patterns over community assembly processes. For example, it is thought that deterministic processes dominate species establishment in early succession while stochastic processes dominate later stages of succession, but how important is the spatial arrangement of soil properties in deterministic or stochastic processes. This research will explore how important are the initial spatial patterns of soil nutrients in determining establishment of species in early succession and how they change through later stages of succession. This data will be incorporated into spatially explicit models of community assembly following changes in land-use in the tropics. Collaborator: Dr. Maria Uriarte.

Effects of intraspecific genetic variation in aspen on soil microbes and soil organic matter pools


Student: Olivia Lopez, Holstrom Environmental Scholar

Much research in ecology has focused on quantifying relationships between biodiversity and ecosystem function to better predict effects of biodiversity loss. Changes in the genetic diversity within a species at the community level can have effects on entire ecosystems and their function. Found in the Great Lakes region of North America, trembling aspen (Populus tremuloides) is a species with large intraspecific diversity. I propose to analyze the effects of genetic variability in trembling aspen on belowground soil communities and resources. My research takes advantage of a long-term field experiment on the effects of disturbance on trembling aspen located at the Arlington Agricultural Research Station in Arlington, Wisconsin. From disturbed (thinned) and control (unthinned) experimental stands, I plan to measure soil microbial biomass, enzymatic activity, nitrogen (N) mineralization and nitrification, soil organic carbon and total nitrogen, and fine root biomass. This study will shed light on the ways in which belowground communities in specific are affected by changes in genetic and phenotypic diversity due to forest disturbance, a phenomenon that is not uncommon in contemporary society. Collaborators: Rick Lindroth and Eric Kruger.

Carbon cycling in biofuel energy cropping systems: measurements and mechanisms of soil organic carbon sequestration


Student: Adam von Haden, PhD 2017

Biofuels are anticipated to become an increasing portion of U.S. agriculture, but the ecological ramifications of such widespread land use change are relatively uncertain. The overall goal of my research is to generate an improved understanding of the controls on carbon loss, storage, and stabilization in model biofuel cropping systems in order to inform environmental, economic, and policy decisions related to bioenergy. My research examines annual net ecosystem primary productivity and explores the drivers of in situ ecosystem carbon losses via heterotrophic and autotrophic respiration in bioenergy cropping systems. In addition, my research seeks to elucidate the mechanisms of soil organic carbon accrual by comparing changes in soil carbon pools following five years of biofuel cropping system establishment. My research is being conducted at the University of Wisconsin-Madison Arlington Agricultural Research Station with additional archived soils from Kellogg Biological Station in Michigan. This work was funded by the Great Lakes Bioenergy Research Center in collaboration with my co-advisors: Dr. Chris Kucharik and Dr. Randy Jackson.

The effects of land use and environmental factors on soil carbon storage in Puerto Rico


Student: Elliot Vaughan, MS 2016

My thesis is looking at different factors that affect soil carbon (C) and nitrogen (N) storage in Puerto Rico. I am particularly interested in how human land use influences soil biogeochemical processes and how land use interacts with environmental factors to determine site-specific responses. I am using samples collected by the Natural Resource Conservation Service (NRCS) at 20 sites across the island. The sites include forest and pasture sites on three different soil types, spanning a range of climate variables. I will be analyzing the data to see which of these variables is most important in determining soil C and N storage.

Soil carbon turnover in response to bioenergy crop treatments in agricultural soils


Student: Laura Szymanski, MS 2015

The objective of this research is to study the effects of different bioenergy crop treatments on soil organic matter stabilization by comparing rates of microbial respiration and soil carbon (C) turnover for soils before and after the establishment of different crops. This will be achieved through the use of archived (2008) soils and new samples collected 5 years (2013) after site establishment at two different sites with different soil mineralogies. Soils will be compared from two depths, 0-10 cm and 25-50 cm to look at changes in soil C dynamics with depth that may occur due to differences in rooting depths with the different bioenergy crop treatments. This research is being conducted with soils from the University of Wisconsin-Madison Arlington Agricultural Research Station and Michigan State University’s Kellogg Biological Station plots in collaboration with the Great Lakes Bioenergy Research Center. Collaborators: Dr. Gregg SanfordDr. Randy JacksonDr. Kate Heckman, and the Radiocarbon Collaborative.

Microbial communities and soil organic matter dynamics during different land-use trajectories 


Student: Emily Atkinson, PhD 2014

The overall objective of this research is to investigate the linkages among aboveground plant diversity, belowground microbial community composition, and soil carbon dynamics to better understand how post-agricultural novel ecosystems affect the process of soil carbon storage. We are studying different land-use trajectories after sugarcane abandonment in the Caribbean island of St. Croix, U.S. Virgin Islands. We are conducting a leaf and root litter decomposition experiment in the field to determine whether microbes from early successional sites dominated by one or two tree species and from more diverse older successional forests are better able to decompose litter from their home environment or if simple, less chemically diverse litter is decomposed faster across sites.

Forest community dynamics during tropical secondary succession

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Student: John Souther, MS 2014

Abandonment of agricultural lands is leading to increased secondary forest cover in parts of Latin America and the Caribbean. This study addresses whether secondary forests on abandoned pastures in Puerto Rico regain key characteristics of mature forests over time. To test changes in structure and composition, we resampled a chronosequence of well-replicated secondary and mature forest plots nine years after the initial census. Specifically, we asked: Does time since establishment affect (1) species composition (2) forest structure (basal area and stem density), and (3) aboveground biomass accumulation? We are comparing rates of change between survey years (2005 and 2012) to changes predicted from the chronosequence approach.    

Linking microbial community structure and function with tropical forest recovery

Sampling forest floor microbial communities

Student: Peyton Smith, PhD 2013

Soil microorganisms regulate fundamental biochemical processes in soil organic matter (SOM) transformations and soil organic carbon (SOC) storage and are thus important drivers for ecosystem processes and biogeochemical cycles. In order to predict how land cover change affects belowground carbon storage, an understanding of how forest floor and soil microbial communities respond to changes in vegetation, and the consequences for SOM formation and stabilization, is fundamental. Using a well-replicated, long-term successional chronosequence, this project investigated the effects of natural post-agricultural forest regeneration on microbial communities and belowground C cycling in Puerto Rico. The research objectives included: (1) characterizing microbial community composition and activity during 90-years of forest recovery on former pastures, (2) investigating links between microbial community structure, function and SOC, and (3) identifying direct links between microbial community composition and microbial functional gene diversity. Collaborators: Dr. Teri Balser and Dr. Marie-Anne de Graaff.

Stabilization of ancient organic matter in buried soils 


Studying paleosols in the central Great Plains. Photo by Joe Mason

Student: Nina Chaopricha, PhD 2013

Most research on soil organic carbon (SOC) investigates soils to a maximum of 1 m depth, but at least a third of global SOC is located deeper. This research explored the importance, sources, composition, and stability of deeply buried soil organic matter through a review of processes contributing to global SOC accumulation in buried soils below 1 m depth and through a case study of SOC preservation in a deeply buried paleosol.  The age, composition and bioavailability of organic compounds persisting in early Holocene loess deposits were analyzed by integrating isotopic, spectroscopic, and geochemical techniques. CollaboratorsDr. Joe MasonDr. Carsten Mueller, Dr. Aaron DiefendorfDr. Alain Plante, and Dr. Stuart GrandyOur research is highlighted in the first minute of this NSF Science Now episode. Check out links to other news outlets reporting on this research on our Home page.

Soil chemistry analysis of an archeological site to reconstruct gardening practices


Student: Emily Eggleston, MS 2012

This project will investigate gardens created by Japanese Americans while interned at Camp Amache, in southeastern Colorado, during World War II. I will evaluate the soil chemistry of the historic garden locations to preserve internment history and also provide unique complementary data for archeological analysis. I will also undertake archival analyses to add to the existing literature on the place that gardening had in the lives of the internees. This project will contribute to the understanding of how the physical environment influenced Japanese Americans internment as well as how the physical environment was influenced in turn by camp internees. Collaborator: Dr. Bonnie Clark at University of Denver.

A landscape-scale study of land use and soil parent material effects on arid soils


Student: Marc Mayes, MS 2011

This project combined GIS, remote sensing, and soil elemental analyses to compare the influence of human and soil forming factors on soil biogeochemistry at a landscape scale, and to study the heterogeneity of soil biogeochemical variables across different sets of land use and soil parent materials in the Konya Basin, Turkey. Collaborators: Dr. Mutlu Ozdogan and Dr. Murray Clayton