Projects - UNH Grandy Lab

Changing precipitation and below ground processes

Tim Bowles

Soil Ecosystem Resilience

Water is a fundamental driver of belowground processes like microbial activity and plant-soil nitrogen cycling. Projections indicate that climate change will affect precipitation patterns (e.g. intensity and seasonality of rainfall) at least as much as precipitation amounts. The Grandy lab has several projects underway to investigate how these changes will affect soil microbes and the critical ecosystem processes they mediate, and how agroecosystem management can be used to adapt to these changes. With collaborators at the Kellogg Biological Station LTER, the lab studies how microbial community structure and activity responds to increasingly long intervals between summer rainfall in annual vs. perennial bioenergy systems, with a particular focus on whether these systems promote more resistant or resilient microbial communities. Another project is developing a framework to understand how changes in precipitation patterns will affect nitrogen cycling and losses in rainfed agricultural systems and how diversification at multiple scales could minimize harmful nitrogen losses in these new conditions.

Does crop rotational diversity increase soil microbial resistance and resilience to drought and flooding?

Jörg Schnecker 

Soil Ecosystem Resilience 

A big challenge for future agriculture is to adapt management practices to establish systems that are able to deal with changes in precipitation regimes. Increasing the number of crops in rotation might be a way to establish such a system by increasing microbial diversity and very likely functional redundancy. In collaboration with long term research stations across the country the Grandy lab is examining if crop rotational diversity increases soil microbial resistance and resilience to drought and flooding.

The Agronomic Relevance and N-Supplying Capacity of Mineral-associated Organic Matter

Andrea Jilling

SOM Formation and Mineral Associated OM

Mineral-associated organic matter (MAOM) is a rich reservoir for N in agricultural soils and often holds 5-7x more N than particulate or labile fractions. However, MAOM is considered largely unavailable to crops as a source of N due to the physicochemical forces on mineral surfaces that stabilize organic matter. Several lines of evidence suggest that mineral-bound organic matter can exchange actively with the soil solution depending on the capacity for soil organisms and organics to compete with or displace organo-mineral associations. In our research, we are exploring whether mineral surfaces mediate plant-microbial interactions in the rhizosphere by regulating the availability of organic N. Plant-microbial interactions in the rhizosphere may also facilitate the turnover of organic nitrogen from mineral surfaces. That is, rhizosphere-induced changes to microbial activity and soil solution chemistry, such as through root exudation, may alter the decomposability and ultimate fate of mineral-bound organic matter. We will investigate possible mechanisms controlling MAOM turnover in the rhizosphere. Ultimately, we aim to assess MAOM’s potential contribution to plant-available N pools in agricultural soils.

Soil organic matter content – a non-linear control on decomposition

Jörg Schnecker

SOM Formation and Organo-Mineral Association

Soil microbes need to be in close proximity to their substrate to be able to efficiently decompose it. With decreasing organic matter content in soils, also the probability that a microbe meets its substrate decreases. In a laboratory incubation experiment the Grandy lab is investigating the effect of spatial separation of microbes and substrate, as a function of organic matter content on microbial strategy for decomposition and decomposition itself.

Microbial Driven Soil Organic Matter Formation

Cynthia Kallenbach

SOM Formation and Organo-Mineral Association 

Soil organic formation is a two-step process that begins with litter decomposition and is followed by the incorporation of carbon into stable SOM pools. It is known that microbes play a critical role in both of these SOM formation steps, but their specific contributions remain undefined and even the newest conceptual and quantitative models of SOM formation largely ‘black box’ the microbial community. We continue research into the relationships between microbial physiology and soil organic matter formation (e.g. Kallenbach et al. 2015; 2016, Nature Communications) and its incorporation into new microbial-explicit soil biogeochemistry models (e.g. Wieder et al. 2014; 2015).

Cover Crop Root and Shoot Contributions to Soil Organic Matter

Emily Austin

Agroecosystem Diversity

The "Cover Crop Root and Shoot Contributions to Soil Organic Matter" project traces belowground (root) and aboveground (shoot) cover crop carbon into soil carbon pools at the Great Lakes Bioenergy Research Center (GLBRC) at the Kellogg Biological Research Station (KBS) in Hickory Corners, MI. We pulse- labeled a winter cereal rye cover crop with 13C- CO2 in a continuous corn with cover crop rotation as part of the Biofuel Cropping Systems Experiment. Prior to corn planting, we transferred the shoot material between plots resulting in one plot with 13C labelled root material and rhizodeposits, one plot with 13C labelled shoot material and one control plot. We traced 13C photosynthate into bulk soil and microbial biomass twenty-four hours following the first labeling event, and found root inputs three times more likely to be retained in soil carbon pools five months following cover crop termination. Further, the greater retention of root carbon was most pronounced in soil pools associated with mineral association and physical protection in aggregates. Our results lend favor to the practice of utilizing cover crop shoot residues as additional feedstock in bioenergy systems.

Roots and arbuscular mycorrhizal fungi influence organic nitrogen cycling differently under high- and low-intensity management

Amanda Daly

N Transformations
 

Roots and associated arbuscular mycorrhizal fungi (AMF) could alter N mineralization dynamics by influencing rhizosphere and hyphosphere microbial community structure and function. This project seeks to determine the extent to which roots and AMF can alter N mineralization by soil microbes, and whether the functional response to root and AMF presence differs in soils with contrasting background microbial communities due to differences in agricultural management.

Improving nitrogen synchrony via biological interactions

Tim Bowles

N Transformations

One of the main reasons for large and harmful losses of nitrogen from intensive cropping systems is a lack of synchrony between when nitrogen is available in soil and when plants need it most. The Grandy Lab works on how roots stimulate soil microbes to potentially release nitrogen from organic sources in concert with plant demand, a phenomenon known as “priming”. In particular, the lab is interested in the role of specialized soil microbes, like arbuscular mycorrhizal fungi, in these processes. In new work with collaborators at UC Davis, the lab will be investigating how rhizosphere functions, including the ability to prime organic nitrogen mineralization, have shifted during modern breeding.

Organic agricultural management modulates the way soil microbial communities process organic nitrogen under drought

Amanda Daly

N Transformations

As climate abnormalities intensify over the coming century, many agronomically-important regions will face more frequent and longer periods of drought interspersed with fewer, more intense precipitation events. Growers will need to adopt effective strategies to sustain crop access to soil nutrients and maintain yields despite low water availability. Agricultural management influences the behavior and composition of soil microbial communities, and could thus help buffer soil function against the negative influences of climate change. In this project we investigate whether organic agricultural management affects how soil microbes depolymerize and mineralize organic N under drought conditions.


Using the MIcrobial-MIneral Carbon Stabilization model with stoichiometrically coupled nitrogen cycling (MIMICS-CN) to understand management responses of agricultural systems

Emily Kyker-Snowman

N Transformations

Recent research points to the role of microbes as mediations of soil C and N cycling, and a new coupled C-N model (MIMICS-CN) explicitly represents this role. Agricultural management of soil carbon (C) and nitrogen (N) is critical to maintaining crop yields while mitigating the environmental impacts of farming. Strategies to increase soil C and N stocks and control the release of N to plants (e.g. reduce tillage, organic fertilizer and residue application, cover cropping) have hightly variable effects and are poorly predicted by first-order models of soil C and N cycling. The aim of this project is to develop MIMICS for use in simulating agricultural management effects on continental scales.

Daycent modeling and comparisons with DNDC modeling approaches for GSB Initiative: Geospatial & environmental analysis of pastureland intensification for bioenergy Task II.

Eleanor Campbell

Soil Biogeochemical Modeling

Crop-based biofuels can provide multiple benefits as a renewable energy source and a replacement for fossil fuels, including reducing the climate impact of fuel production and combustion. However, the location of crop-based biofuel production impacts its sustainability, as it may conflict with protection of native ecosystems or the capacity to meet food production demands. Pasture lands account for a greater percentage of agricultural land area than crop lands, and have greater potential to be managed more intensively (i.e. higher production per unit of land area). This project aims to assess the capacity for more intensive, sustainable pasture management to free active agricultural land to increase the production of crop-based bioenergy feedstocks. The DayCent model will be used to assess the soil biogeochemical impacts of intensive pasture management practices and land use conversion into crop-based bioenergy, focusing on soil carbon and greenhouse gas flux.