Carbon cycling in biofuel energy cropping systems: measurements and mechanisms of soil organic carbon sequestration
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.
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
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 Sanford, Dr. Randy Jackson, Dr. Kate Heckman, and the Radiocarbon Collaborative.
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.
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
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
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. Collaborators: Dr. Joe Mason, Dr. Carsten Mueller, Dr. Aaron Diefendorf, Dr. Alain Plante, and Dr. Stuart Grandy. Our 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.
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
Hydrologic transport of soil organic matter and nutrients
The composition and quantity of dissolved organic matter (DOM) retained or lost from soils has implications for carbon sequestration, soil fertility, water quality, and the productivity of riparian and coastal communities. Past research addressed the production and fate of DOM in highly productive, wet tropical forest volcanic soils in Hawai’i. The hydrology of these soils appears to drive the transport of labile C from the forest floor and zones of highest microbial activity to deeper mineral horizons, where the potential for stabilization is greatest. How will changes in hydrology and rainfall patterns alter these processes and affect the potential of soils to retain nutrients and sequester carbon? Collaborators: Dr. Oliver Chadwick and Dr. Marc Kramer
Legacies of land use on aboveground C and species diversity
Socioeconomic changes across the tropics are leading to widespread agricultural abandonment and the regrowth of secondary forests. Reforestation provides opportunities for the recovery of forest ecosystem goods and services and for C sequestration in plant biomass and in soils. In a land-use chronosequence of secondary forests regrowing on abandoned pastures in Puerto Rico, forest structural characteristics were recovered in as early as 20 years. Tree species composition, however, remained distinct from primary forests even after 80 years, affecting C storage in aboveground biomass. Will novel species assemblages continue to provide the same important ecosystem goods and services? How resilient will these ecosystems prove to be to future climatic change and other disturbances? Collaborators: Dr. Whendee Silver and Dr. Rebecca Ostertag
Legacies of land use change on belowground carbon across a successional chronosequence
Many international policies assume that reforestation will result in C sequestration above- and belowground. However, many factors control the response of soil C to land-use and land-cover change. In a secondary forest chronosequence in Puerto Rico, soil C dynamics did not reflect the increase in aboveground biomass with reforestation. The gain in new, secondary forest-derived C was compensated for by the loss of residual pasture-derived C, resulting in no net change in bulk soil C pools. How do we restore fertility to degraded soils and how best do we conserve soil organic matter reserves during multiple cycles of land use? Collaborators: Dr. Whendee Silver, Dr. Rebecca Ostertag, Dr. Chris Swanston
Mechanisms of soil organic matter stabilization in reforested pastures
Physical and chemical fractionation methods are useful for understanding the dynamics of different components of SOM when bulk measurements are too coarse. Isotopic and 13C-NMR analyses revealed that C associated with soil aggregates differed from unassociated particulate C. The majority of the soil C pool with longest 14C mean residence times was recovered in the mineral-associated fraction, providing evidence for the importance of physical protection mechanisms. Turnover rates of the mineral-associated C in secondary forests recovering from abandoned pasture resembled those of primary forests in as little as 20 years, reflecting patterns in aboveground stem dynamics. In the active pastures and youngest secondary forests, mean residence times of the aggregate and mineral-associated C fractions differed from older secondary forests and primary forests, likely due to site differences in litter chemistry and soil disturbance. How do land use and land cover change affect the relative importance of physical and chemical mechanisms of organic matter stabilization and what are the consequences for C sequestration and nutrient retention in soils? Collaborators: Dr. Chris Swanston, Dr. Margaret Torn, Dr. Sarah Burton, Dr. Whendee Silver.