Current Research

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

Student: Olivia Lopez, Holstrom Environmental ScholarOLYMPUS DIGITAL CAMERA

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. 


IMG_2658.JPGPhD Student: Chase Kasmerchak

Within the experimental aspen stands at Arlington Agricultural Research Station, there are distinct differences in litter chemistry between genotypes, specifically with condensed tannin (CT) and phenolic glycosides. Differences in litter chemistry affect decomposition rates and ultimately, the relative proportions of carbon that is readily available for microbial decomposition and carbon that is bound and protected within soil aggregates. The plots at our research site include populations of high and low tree density plots. Low tree density plots are meant to resemble the modern silviculture management practice of intermediate thinning, while high density plots are meant to resemble unthinned forests. To better understand how differences in litter chemistry effect soil microbial activity, I will conduct a laboratory incubation using soil from the high and low tree density environments and tree litter from two genotypes – one with high CT and one with low CT contents. This experiment will allow us to measure microbial activity directly through rates of CO2 and N2O production. I will also look at the carbon content within aggregate fractions and readily accessible carbon from field soils, along with in-situ formation of aggregates in the lab using artificial soil, tree litter, and microbial inoculum from the field soils. By linking these data to rates of mineralization and nitrification, and the composition and function of soil microbial communities, we will better understand how forest management strategies effect nutrient cycling, element transformations, and longer-term carbon storage in forests with varying degrees of genetic diversity. 


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

Masters Student: Emily J. Diaz Vallejo20190111_103304

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.

Environmental controls on soil carbon storage and turnover in the Caribbean

20190112_153101PhD Student: Elliot Vaughan

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.

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.

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

Brady soil Marin-SpiottaPhD student: Laura Szymanski

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.

Nitrogen cycling during tropical forest succession

Student: Sanober Mirza, Holstrom Environmental Scholar

The objective of this project is to quantify the variation in different nitrogen (N) cycling processes with forest succession. Nitrogen plays two important roles in Earth’s climate. As a plant nutrient, the availability of N affects plant growth and the uptake of carbon (C) from the atmosphere into plant biomass. The accumulation of C in long-lived biomass and in soils contributes to reducing the amount of CO2 in the atmosphere. Secondly, excess N can lead to the production of N2O, which is a more potent greenhouse than CO2. Land-use change, specifically deforestation and reforestation, can affect N availability for plant growth and N2O production. Long-term agricultural use can deplete nitrogen sources, even in tropical soils where N is not expected to limit productivity. Through the evaluation of nitrogen-fixing tree species, N in litterfall, soil N, and N mineralization, we will gain a comprehensive picture of tropical N-cycle variation. Soils have been sampled from a well-replicated chronosequence in Puerto Rico with pastures, 29-year-old forests, 69-year-old forests, and primary forest. The results from this study can be applied to forest management and land-use decisions, with implications for the global climate.

ADVANCE Partnership: From the Classroom to the Field: Improving the Workplace in the Geosciences

Website photosThe geosciences is one of the least diverse disciplines in STEM. One reason for this is the hostile climate experienced by many women and people of color in the geosciences due to sexual and racial harassment. This collaborative project with the Earth Science Women’s Network, the Association for Women Geoscientists and the American Geophysical Union aims to improve work climate conditions and increase gender equity in the geosciences by developing bystander intervention workshops for department heads, chairs, and faculty to appropriately respond to, prevent, and eliminate sexual harassment. Goals include sexual harassment awareness and prevention training in the teaching of ethical conduct in research guidelines; developing and incorporating geoscience-relevant scenarios in training and teaching materials, including field research and educational settings; incorporating experiences of community members with intersectional identities who may face sexual, racial and gender harassment, and collaborating with professional society partners for national dissemination, implementation, and sustainability. Funded by NSF ADVANCE Partnership program. Team members include: Billy Williams, American Geophysical Union; Blair Schneider, Association for Women Geoscientists; Allison Mattheis, California State University, Los Angeles; and leaders from the Earth Science Women’s Network: Rebecca Barnes, Colorado College; Asmeret Berhe, University of California, Merced; and Meredith Hastings, Brown University. Project assistants on the team are Haley Burkhardt and Sunita NandihalliHaley is a second year graduate student in Biological Anthropology who has been a critical part of the PEOPLE program serving new students to campus, and especially Native students. Sunita is a new masters student in the Counseling Psychology program with research experience on cross-cultural studies.