Source: UNIVERSITY OF NEW HAMPSHIRE submitted to
MEASURING AND PREDICTING SOIL ORGANIC MATTER FORMATION AND NITROGEN MINERALIZATION
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
NEW
Funding Source
Reporting Frequency
Annual
Accession No.
1007001
Grant No.
(N/A)
Project No.
NH00633
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Oct 1, 2015
Project End Date
Sep 30, 2019
Grant Year
(N/A)
Project Director
Grandy, A.
Recipient Organization
UNIVERSITY OF NEW HAMPSHIRE
(N/A)
DURHAM,NH 03824
Performing Department
Natural Resources and the Environment
Non Technical Summary
Soil organic matter (SOM) influences most key soil processes including water holding capacity, soil aggregation and structural formation, porosity, and erosion potential. SOM also influences a number of ecosystem scale processes including trace gas emissions and net primary productivity and plays a central role in the global C cycle. Scientists, policy makers, and land managers have long appreciated the importance of SOM. This is reflected in historical references to its role in agricultural productivity dating back thousands of years, and in more recent scientific efforts to understand how it is formed and its function in soil. While progress has been made in this regard, the processes underlying the formation of soil organic matter remain poorly defined, and the contributions SOM makes to plant N availability have not been quantified. Moreover, soil biogeochemistry models do not explicitly account for the contributions microbes make to SOM dynamics and nitrogen (N) availability.The goals of this project are to examine: 1) Plant and microbial contributions to soil organic matter accumulation; 2) N mineralization and its microbial and mineralogical controls; and 3) Soil biogeochemistry model structures that incorporate microbial communities and processes.
Animal Health Component
0%
Research Effort Categories
Basic
50%
Applied
40%
Developmental
10%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
10201991070100%
Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships;

Subject Of Investigation
0199 - Soil and land, general;

Field Of Science
1070 - Ecology;
Goals / Objectives
The overriding goal of this project is to understand the mechanisms by which soil microbes regulate soil C and N cycling, and to incorporate these mechanisms into soil biogeochemistry models. The overarching goals of this research areGoal 1. Examine plant and microbial contributions to soil organic matter (SOM) accumulation.Goal 2. Examine N mineralization and its microbial and mineralogical controls.Goal 3. Examine soil biogeochemistry model structures that incorporate microbial communities.The specific objectives over the four years of this project are.Objective 1. Quantify the variation in microbial physiological traits driving SOM formation in organic and conventional agricultural soils.Objective 2. Develop and apply new laboratory methods for examining plant and microbial lipids in soil organic matter.Objective3. Ascertain how clay mineralogy influences the direction and size of nitrogen priming effects.Objective 4. Determine how microbial community composition and activity interact with clay content and type to control priming effectsObjective 5. Determine how clay texture and mineralogy control microbial priming of mineral-associated N.Objective 6. Explicitly simulate microbial activity and physiology inMIcrobial-MIneral Carbon Stabilization model (MIMICS), and improve model predictions under changing environments.
Project Methods
Objective 1:Temporal variability in microbial physiology due to agricultural management will be assessed by comparing microbial growth efficiency (MGE) and rate (MGR) in organic and conventional cropping systems over two-year-long cropping cycles. These observed differences in physiology will be linked with how new C inputs are processed into various soil C pools using in situ field additions of isotopically labeled C substrates. I will track 13C-labeled glucose, glutamic acid, and oxalic acid into microbial biomass and soil C fractions. These substrates represent typical new plant C inputs from root exudates and crop residues and differ in their complexity and quality. The substrate quality gradient will determine if higher resource quality inputs have the potential to divert more C into more stable SOM. Using a physical fractionation protocol adapted from Balesdent (1987), soils will be isolated into a particulate organic matter fraction (>63mm), a mineral fraction (63-2000mm), and three organo-mineral fractions (20-63mm, 2-20mm, and <2mm). The organo-mineral fractions tend to contain the most stable SOM with a greater abundance of microbial compounds relative to plant-derived products, making this pool a useful indicator of stable microbially-derived SOM. Objective 2. Lipid biomarker analyses will determine how differences in observed C allocation strategies influence the production of stable microbially-derived SOM. A subset of the soil samples for all time steps used for MGE and MGR will be analyzed for microbial lipid biomarkers within the different soil size classes. Microbial residue contributions to SOM will be analyzed using lipid profiling (Feng and Simpson, 2011). Soil lipids, including branched short-chain (<C20) alkanoics and hopanoids indicative of microbially-derived SOM, will be isolated by solvent extractions methods. These compounds are then identified via GC/MS. Microbial lipids make up a large portion of microbial biomass and are a significant component of microbially-derived SOM and thus provide a useful proxy for microbial residues.Objective 3. Ascertain how clay mineralogy influences the direction and size of nitrogen priming effects. I will gather two soils with a high clay content (50-60%) and contrasting mineralogy (kaolinitic and smectitic clays). After sterilizing, I will add sand at different levels to create soils with 10, 20, 30, 40, and 50% clay concentration. I will create two microbial inocula from contrasting agricultural management treatments with known differences in microbial community composition. I will add sterilized soils to an open-bottom incubation system that allows for both respiration to be monitored and leachate to be collected. At the beginning of the incubation, I will treat soil texture and mineralogy in a factorial design with the inoculum, then add exudates as a combination of 13C labeled glucose, glutamate, and oxalate in amounts representative of common root exudates every 7 d. 24 hours following substrate addition, I will destructively harvest one replicate set of microcosms, and pass water through the remaining microcosms to collect leachate. I will follow with four subsequent rounds for a total of five harvests. A sixth replicate set of microcosms will be reserved for daily measurement of CO2 respiration. Objective 4. To quantify the influence of clay content and type on N priming, I will quantify soil C and N pools across the soil texture treatments as follows. I will measure dissolved organic N and C (DON, DOC), nitrate and ammonium concentrations in leachate and potassium chloride (KCl) extracts from whole soil. From whole soil I will also quantify microbial biomass C and N (MBC, MBN), total soil C and N, and net proteolysis at two time points with the fluorometric OPAME procedure. This is an important measure as there is increasing evidence that the primary amine pool plays a significant role in N availability. I will measure rates of N mineralization, ammonification, and nitrification by isotope pool dilution. Priming will be calculated as the difference in respiration and N transforming processes (proteolysis, N mineralization, etc.) between the samples with and without labile C additions.Objective 5. Determine how clay texture and mineralogy control microbial priming of mineral-associated N. I will include clay content and microbial inoculum in a nested ANOVA to see which main factor most influences N transforming processes in my microcosms, and whether these factors interact. To further evaluate microbial community structure and activity, I will apply 13C phospholipid fatty acid (PLFA) analysis to determine which microbial groups are assimilating the C substrate. I will also measure activity of microbial extracellular enzymes involved in N acquisition using fluorometric substrates NAG, TAP, and LAP. I will regress these measures of microbial activity and function against priming indices to determine whether microbial and mineral characteristics and can explain part of the priming dynamics I observe. I will collect soils with a wide range of clay content from across 30 agricultural systems. From these soils, I will measure N availability, along with soil physical and chemical properties and ARISA fingerprints of soil microbial communities. I will collapse multivariate variables (such as ARISA fingerprints) into axis scores using nonmetric multidimensional scaling analysis, and use multiple linear regression to determine whether clay content contributes significantly to variation in N availability in situ, after accounting for other environmental factors.Objective 6. Explicitly simulate microbial activity and physiology inMIcrobial-MIneral Carbon Stabilization model (MIMICS), and improve model predictions under changing environments. Similar to microbial physiology, the chemical quality of litter inputs and physical stabilization of microbial residues regulate soil C dynamics but are poorly represented by model structures. Addressing these uncertainties, Grandy and colleague Will Wieder developed the MIMICS model to explore theoretical interactions among substrate quality, microbial community composition, and the formation of stable soil C in different soil environments. Model results emerge from MIMICS because of assumptions made about microbial community tradeoffs in MGE and MGR, as well as about the effects of soil texture on the physical stabilization of microbial residues. The extent to which microbial physiology and physical protection of soil C can be constrained by observations remains uncertain, but overcoming this technical challenge is critical for resolving potential effects of microbial functional diversity in soil biogeochemical models. The focus of the proposed MIMICS research will be to refine parameterizations and validate model output related to: (1) quantify the ecophysiological variation of microbial functional types (MGE and MGR); (2) evaluate the physical protection of microbial residues that can form stable soil C; and (3) explore how microbial physiology and physical protection of soil C respond to agricultural management practices. Grandy and collaborators will collect data from published literature and targeted experimental studies to help constrain and inform MIMICS parameterizations and responses to agricultural management practices. Grandy and colleagues will focus on physiological mechanisms that may favor physical vs. biochemical protection of soil C across gradients of soil texture, site fertility, and management practices (including residue management and tillage practices). Using a combination of techniques, Grandy and collaborators will quantify MGE and MGR with stable isotopes, evaluate the relative contribution and chemical modification of microbial residues to the formation of mineral stabilized soil C, and quantify how agricultural management modifies microbial community composition and activity.

Progress 10/01/17 to 09/30/18

Outputs
Target Audience:The target audience includes other scientists and land managers receiving information about this project from papers and presentations and students that are young scientists training in the PI's lab or taking his classes. Courses:The research conducted in this project is incorporated into NR 797, Environmental Soil Chemistry. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Postdoctoral scientist Emily Austin and Grandy Lab Ph.D. students Amanda Daly, Andrea Jilling, Lauren Breza, Emily Kyker-Snowman and M.Sc. student Bennett Thompson all contributed to the project. All Grandy lab students and postdocs have attended national or international meetings in the past year where their current research was presented, and continue developing advanced approaches to understanding soil organic matter and nitrogen dynamics. The postdoc and graduate students have been provided with teaching opportunities in my lab and classes, and all have participated in teaching classes and leading lab group meetings. Further, all have been given the opportunity to develop new collaborations with my colleagues. My lab has also provided seven undergraduate students during this period with opportunities to participate in ongoing projects, and two of these students presented at undergraduate research conferences. How have the results been disseminated to communities of interest?The work was shared with the scientific community in published conference presentations including multiple invited talks and six journal publications including Nature Sustainability. A highlight includes a keynote presentation to producers, industry, and scientists at the Soil Health Institute Annual Meeting, which was also recorded and has been viewed on Youtube more than 600 times, https://www.youtube.com/watch?v=-W4C1vte4eA What do you plan to do during the next reporting period to accomplish the goals?We will continue to train undergraduate and graduate students in the challenges related to understanding and managing the N cycle. We will carry out additional experiments to attempt to understand the role of different soil pools in providing plants and microbes nitrogen. In an effort to disseminate our results we will give to talks at scientific conferences and stakeholder meetings, as well as publish in top-tier journals. We will also leverage our Hatch funds to compete for additional external grants to advance the conceptual basis of the soil N cycle.

Impacts
What was accomplished under these goals? Impact. Globally, humans add approximately three-fold more biologically available nitrogen (N) to terrestrial ecosystems than natural sources, primarily with synthetic fertilizers and legumes. This vast amount of N has substantially increased crop yields, but the majority of agricultural N inputs are not actually taken up by crops. Instead, much of this N is lost from agricultural fields, with wide-ranging impacts across local, regional, and global scales, including declines in water quality and biodiversity in terrestrial, aquatic, and marine ecosystems and increases in emissions of the greenhouse gas nitrous oxide (N2O). Losses of nitrogen from agriculture are thus major threats to environmental and human health at local, regional, and global scales. Emerging evidence shows that climate change and intensive agricultural management will interact to increase these harmful effects and undermine current mitigation efforts. Identifying effective mitigation strategies and supporting policies requires an integrated understanding of the processes underlying potential agricultural N responses to climate change. In an interdisciplinary review published this year, we describe these processes, propose a set of agroecological principles to guide research and policy for decreasing nitrogen losses in the future, and describe the economic factors that could constrain or enable their implementation. Second, we published a conceptual framework to challenge current assumptions about N mineralization, a key source of N in all soils. N mineralization involves the conversion of organic to plant-available inorganic N. Existing concepts ignores the role of microbial communities in N mineralization. We show that microbial communities and their physiology are strong controls over N mineralization and this N availability. This work could ultimately lead to managing soils to foster more N efficient microbial communities that deliver N to plants when they need it most. Objective 1. Quantify the variation in microbial physiological traits driving soil organic matter (SOM) formation in organic and conventional agricultural soils. This objective was completed and reported on in a previous report. Objective 2. Develop and apply new laboratory methods for examining plant and microbial lipids in soil organic matter. We changed directions on this objective and instead focused on the development of new laboratory methods for amino acid gross flux dynamics. This is a novel method that we are the first lab in the U.S. to optimize, advancing our dual objectives of better understanding SOM dynamics and N cycling. Objective 3. Ascertain how clay mineralogy influences the direction and size of nitrogen priming effects. This objective was completed and reported on in a previous report. Objective 4. Determine how microbial community composition and activity interact with clay content and type to control priming effects. This objective was completed and reported on in a previous report. Objective 5. Determine how clay texture and mineralogy control microbial priming of mineral-associated N. We have been conducting experiments to determine how plant root exudates, microbial communities, and clay minerals interact to control soil nitrogen availability. We examine a commonly overlooked but potentially important source of nitrogen: organic matter bound to clay particles. Although generally considered inaccessible to plants, we explore how plant root exudates drive the microbial and non-biological release of nitrogen from clay associations.To test this hypothesis, we conducted laboratory incubation in which we applied exudate-like compounds to soils composed of only sand and physically-isolated,mineral-associated organic matter (MAOM). The use of stable isotopically-enriched carbon additions allowed me to detect the proportion of CO2 respired that was derived from externally-applied carbon or from the soil organic matter. Carbon additions stimulated microbial activity, extracellular enzyme production, and the subsequent breakdown of MAOM-derived carbon and nitrogen. We found C additions stimulated CO2 respiration and MAOM degradation. Compared to the control, glucose and oxalic acid-treated soils respired 139% and 89% more C, respectively. In both cases, we also observed a net positive priming effect indicating that microbes were releasing C from MAOM at a faster rate than in the control. The magnitude of this priming effect was significant: increases of 200-400% in glucose treatments and up to 280% in oxalic acid treatments. Likewise, C treatments stimulated C/N-acquiring and oxidative enzyme activities, although the response was specific to the substrate. Glucose additions specifically enhanced the production of an exo-cellulase and a chitinase, while oxalic acid suppressed most N-acquiring enzyme activities and enhanced peroxidase and phenoloxidase activities. Finally, gross ammonium production was positively associated with the priming of MAOM-C. Our results indicate that common root exudates, like glucose and oxalic acid, can significantly increase the turnover and potential release of C and N from MAOM. This work continues in the work that we propose here. Objective 6. Explicitly simulate microbial activity and physiology inMIcrobial-MIneral Carbon Stabilization model (MIMICS), and improve model predictions under changing environments. Here, we used our newly developed MIMICS C model with coupled N cycles and data synthesis to examine how climate-change driven alterations in precipitation patterns are likely to affect N cycling and losses in agricultural landscapes and to highlight promising interventions to minimize environmental N losses while maintaining or increasing productivity. As a case study, we consider the Central U.S., a globally-important agricultural production region for cereal (maize and wheat) and soybean production. We review climate projections for the region and then highlight key water-N linkages and the vulnerability of N to environmental loss and incorporate these findings into models. Our modeling efforts show the importance of system-wide solutions (e.g. the use of cover crops) to address N losses from agroecosystems (Bowles*, T.M., Atallah, S.S., Campbell, E.A., Gaudin, A.C.M., Wieder, W.R. and A.S. Grandy. 2018. Agricultural nitrogen losses in a changing climate: Processes, predictions, and agroecological solutions, Nature Sustainability, 1:399-408. Featured in USDA NIFA Blog. https://nifa.usda.gov/blog/unh-recommendations-seek-help-farmers-curb-agricultural-nitrogen-losses).

Publications

  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Rothstein, D.R., Toosi, E.R., Schaetzl, R.J., and A.S. Grandy. 2018. Direct delivery of carbon from surface organic horizons to the subsoil in coarse-textured Spodosols: Implications for deep soil C dynamics, Soil Science Society of America Journal, 82:969-982.
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Lombardozzi, D.L., G. B. Bonan, W. Wieder, A. S. Grandy, C. Morris, and D. L. Lawrence. Cover crops may cause winter warming in snow-covered regions. Journal of Geophysical Research Letters, 45: 9889-9897. Featured in Science Daily https://www.sciencedaily.com/releases/2018/12/181219093855.htm and multiple other online reports including European Scientist.
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Siders, A.C., Z.G. Compson, B.A. Hungate, P. Dijkstra, G.W. Koch, A.S. Wymore, A.S. Grandy, J.C. Marks. 2018. Litter identity affects assimilation of carbon and nitrogen by a shredding caddisfly, Ecosphere, 9(7):e02340, doi.org/10.1002/ecs2.2340
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Whalen, E.D., R.G. Smith, A.S. Grandy, and S.D. Frey. 2018. Manganese limitation as a mechanism for reduced decomposition in soils under atmospheric nitrogen deposition. Soil Biology & Biochemistry,127:252-263
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Jilling, A., Contosta, A.R., Frey, S., Scimel, J., Schnecker, J., Smith, R.G., Tiemann, L., and A.S. Grandy. Minerals in the rhizosphere: overlooked mediators of soil nitrogen availability to plants and microbes, Biogeochemistry, doi:10.1007/s10533-018-0459-5
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Bailey, V.L., B.B. Lamberty, K. DeAngelis, A.S. Grandy, C.V. Hawkes, K. Heckman, K. Lajtha, R.P. Phillips, B.N. Sulman, K.E.O. Todd-Brown, and M.D. Wallenstein. 2017. Soil carbon cycling proxies: understanding their critical role in understanding climate change feedbacks, Global Change Biology, doi:10.1111/gcb.13926
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Melillo, J.M., S.D. Frey, K.M. DeAngelis, W.J. Werner, M.J. Bernard, F.P. Bowles, G. Pold, M.A. Knorr, A.S. Grandy. 2017. Long-term Pattern and magnitude of soil carbon feedback to the climate system in a warming world., Science, 358:101-105
  • Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Bowles, T. M., Grandy, A. S., et. al. Crop Rotation Diversity and Yield Resilience: Evidence from 11 Long-Term Experiments in North America Across a Precipitation Gradient. Soil Science Society of America, Annual Meeting, Tampa, FL. October 22-25, 2017.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: DeAngelis, K., &, Grandy, A. S. et. al. Mechanisms of Microbial Destabilization of Soil C Shifts Over Decades of Warming. American Geophysical Union, Fall Meeting, New Orleans, LA. December 11-15, 2017.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Kyker-Snowman, E., Wieder, W. R., and Grandy, A. S. Different Mechanisms of Soil Microbial Response to Global Change Result in Different Outcomes in the MIMICS-CN Model. American Geophysical Union, Fall Meeting, New Orleans, LA. December 11-15, 2017.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Jilling, A., Grandy, A. S., and Keiluweit, M. The Potential Bioavailability of Mineral-Associated Organic Nitrogen in the Rhizosphere. American Geophysical Union, Fall Meeting, New Orleans, LA. December 11-15, 2017.
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Bowles, T.M., Atallah, S.S., Campbell, E.A., Gaudin, A.C.M., Wieder, W.R. and A.S. Grandy. 2018. Agricultural nitrogen losses in a changing climate: Processes, predictions, and agroecological solutions, Nature Sustainability, 1:399-408. Featured in USDA NIFA Blog. https://nifa.usda.gov/blog/unh-recommendations-seek-help-farmers-curb-agricultural-nitrogen-losses
  • Type: Other Status: Other Year Published: 2018 Citation: Breza, L., &.., Grandy, A.S. Soil management practices, not stoichiometric needs, drives microbial activity in agriculture soils. UNH Graduate Research Conference. Durham, NH. April 1, 2018.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2018 Citation: Jilling, A. and Grandy, A.S. 3 Clay minerals: Overlooked purveyors of soil nitrogen. Ecological Society of America, Fall Meeting, New Orleans, LA. August 5-10, 2018
  • Type: Conference Papers and Presentations Status: Other Year Published: 2018 Citation: Jilling, A., Keiluweit, M., and A.S. Grandy. Priming mechanisms providing plants and microbes access to mineral-associated organic nitrogen. Ecological Society of America Conference, New Orleans, LA, August 5-10, 2018
  • Type: Conference Papers and Presentations Status: Other Year Published: 2018 Citation: Keynote: Microbial Physiology Regulates How Much Soil Organic Matter becomes Crop Residue. Soil Health Institute Annual Meeting, Albuquerque, NM, 8/2018.


Progress 10/01/16 to 09/30/17

Outputs
Target Audience:The target audience includes other scientists and land managers receiving information about this project from papers and presentations and students that are young scientists training in the PI's lab or taking his classes. Courses. The research conducted in this project is incorporated into NR 797, Environmental Soil Chemistry; and also NR 795, Soil Fertility and the Environment. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Postdoctoral scientists Emily Austin, Tim Bowles, and Joerg Schnecker, and Grandy Lab Ph.D. students Amanda Daly, Andrea Jilling, Lauren Breza, Emily Kyker-Snowman and M.Sc. student Bennett Thompson all contributed to the project. All Grandy lab students and postdocs have attended national or international meetings in the past year where their current research was presented, and continue developing advanced approaches to understanding soil organic matter and nitrogen dynamics. The postdocs and graduate students have been provided with teaching opportunities in my lab and classes, and all have participated in teaching classes and leading lab group meetings. Further, all have been given the opportunity to develop new collaborations with my colleagues. My lab has also provided seven undergraduate students during this period with opportunities to participate in ongoing projects, and two of these students presented at undergraduate research conferences. How have the results been disseminated to communities of interest?The work was shared with the scientific community in 5 published conference presentations and several journal publications. We gave multiple presentations to the scientific community, which included 12 invited talks at national/international conferences or universities. What do you plan to do during the next reporting period to accomplish the goals?To address the role of clays and priming in Soil Organic Matter (SOM) dynamics, we will continue to examine whether mineral-associated organic matter is accessible to microbes and ultimately to plants? Do soluble rhizodeposits enable microbes to access mineral-bound nitrogen through directly desorbing/liberating mineral-bound compounds? Through stimulating microbes that are more adept at interfering with sorptive interactions (i.e. targeted enzyme production)? Or through stimulating microbial activity to a point of N-starvation and N-desperation? Along with answering these questions, we are also examining with field and lab experiments how does management (tillage and cover cropping) impact the chemical composition of clay-associated SOM and/or dominant binding mechanisms? How do these impacts influence the N-priming capacity and the N-priming response more generally? We continue to also work on the nitrogen cycle and incorporate it into models. We are fine-tuning a new nitrogen mineralization technique, based upon depolymerization by isotope pool dilution of 15N-labeled amino acids coupled with analysis by Gas Chromatography quantitative Mass Spectrometry (GCqMS), and nitrogen mineralization (nitrification and ammonification, as well as N immobilization) by isotope pool dilution of 15N labeled NH4+ or NO3-. The quantification of protein depolymerization using amino acid pool dilution and GC-qMS is a recently developed method, which in the last year has been undergoing improvement and optimization in Grandy's lab at UNH under the direction of a postdoc who helped develop the original method. We have also begun and will continue incorporating nitrogen into MIcrobial-MIneral Carbon Stabilization Model MIMICS. ?

Impacts
What was accomplished under these goals? Impact. Nitrogen availability often limits agricultural yields. Modern intensive agricultural systems are productive due to fertilizer nitrogen? N inputs but N inefficient, resulting in environmental N losses that degrade water quality and increase atmospheric nitrous oxide (N2O) concentrations. Climate change is projected to worsen these environmental N losses by altering precipitation patterns and temperature. Common practices to reduce N losses from agricultural systems focus on reducing fertilization with only limited success, while largely ignoring the provisioning of N by internal, microbial-driven processes. Despite this, agricultural plants typically get more than half of their N from internal sources and microbial processes rather than fertilizers. This year we developed new conceptual models and experiments to explore the simple but challenging question: from where and how do plants get their nitrogen? First, we have developed a robust series of conceptual models arguing that a previously 'hidden' pool of nitrogen is a major supplier of plant N. This pool is mineral-associated organic matter (MAOM), a potentially large and rich reservoir for N in soils. MAOM N is currently considered largely unavailable to plants due to the physicochemical forces on mineral surfaces that stabilize organic matter. We argue that in hotspots around roots, MAOM an important source of nitrogen for plants. Several biochemical strategies enable plants and microbes to compete with mineral-organic interactions and effectively access MAOM. Working together, plant breeders, soil scientists and microbial ecologists will find ways to develop cropping systems whereby the plants can access this large N pool on demand, reducing need for fertilizer N. Second, we have developed conceptual frameworks and experiments to challenge current assumptions about N mineralization, a key source of N in all soils. N mineralization involves the conversion of organic to plant-available inorganic N. Existing concepts ignore the role of microbial communities in N mineralization. We are accumulating evidence that microbial communities and their physiology are strong controls over N mineralization and this N availability. This work could ultimately lead to managing soils to foster more N efficient microbial communities that deliver N to plants when they need it most. Objective 1. Quantify the variation in microbial physiological traits driving SOM formation in organic and conventional agricultural soils. This objective was completed and reported on in theprevious report. Objective 2. Develop and apply new laboratory methods for examining plant and microbial lipids in soil organic matter. Work on this objective has not begun. Objective 3. Ascertain how clay mineralogy influences the direction and size of nitrogen priming effects. We have developed a conceptual model that outlines how clays and clay mineralogy influence the priming of soil N. We synthesized exiting literature and emerging evidence and developed new conceptual models from both the ecological and biogeoscience communities to argue that while depolymerization is a critical first step, clay minerals may be an important and overlooked mediator of bioavailable N, and especially in the soil rhizosphere where they are both a large source and sink for N. Mineral-associated organic matter (MAOM) is a rich reservoir for N in soils and can hold up to 20x more N than particulate fractions. MAOM fractions also preferentially accumulate N compounds such as proteins, amino acids, and nucleic acids. While some MAOM is protected from degradation, other MAOM can be mobilized by plants, microbes, and their interactions, leading to substantial amounts of MAOM-derived N in the soil solution. (Jilling, A., Keiluweit, M., Contosta, A.R., Frey, S., Schimel, J., Schnecker, J., Smith, R., Tiemann, L., Grandy, A.S. (Accepted with revisions). Minerals in the rhizosphere: overlooked mediators of soil nitrogen bioavailability. Biogeochemistry) Objective 4. Determine how microbial community composition and activity interact with clay content and type to control priming effects. Our literature synthesis and conceptual model development now pointthe way forward for how microbial communities interact with clays to influence the biovailability of N. The availability of N to plants is partly regulated by root-associated microbes and their access to and utilization of soil nutrients. As such, specific properties of rhizosphere microbes, such as composition, abundance, and physiology, may mediate the magnitude or direction of the priming effect and the amount of MAOM destabilized via priming. For example, we show the C and N use efficiency (CUE, NUE) of the microbial community coupled with its cellular stoichiometry will determine nutrient demand. As microbial CUE increases, N demand and NUE also increase to maintain cellular C/N ratios. With increasing N demand as microbial CUE and NUE increase, the microbial N-mining response to root exudation should also increase. That is, as root exudates provide a labile C source and microbial C needs are satisfied, microbes will invest more in enzymes to acquire N from MAOM. In contrast, microbes that use C inefficiently will require less N, and will show a depressed N mining response to root exudation. Further, microbial CUE and NUE also constrain microbial community size, turnover, and activity, which will have feedbacks to the cycling and bioavailability of MAOM N. (Jilling, A., Keiluweit, M., Contosta, A.R., Frey, S., Schimel, J., Schnecker, J., Smith, R., Tiemann, L., Grandy, A.S. (Accepted with revisions). Minerals in the rhizosphere: overlooked mediators of soil nitrogen bioavailability. Biogeochemistry) Objective 5. Determine how clay texture and mineralogy control microbial priming of mineral-associated N. We have been conducting been conducting experiments to determine how plant root exudates, microbial communities, and clay minerals interact to control soil nitrogen availability. W examine a commonly overlooked but potentially important source of nitrogen: organic matter bound to clay particles. Although generally considered inaccessible to plants, we explore how plant root exudates drive the microbial and non-biological release of nitrogen from clay associations. To test this hypothesis, we conducted laboratory incubation in which we applied exudate-like compounds to soils composed of only sand and physically-isolated MAOM. The use of stable isotopically-enriched carbon additions allowed me to detect the proportion of CO2 respired that was derived from externally-applied carbon or from the soil organic matter. Carbon additions stimulated microbial activity, extracellular enzyme production, and the subsequent breakdown of MAOM-derived carbon and nitrogen. In follow-up experiments, we will test a wider array of soil types to assess how differences in clay composition and microbial community mediate the soil's response to carbon additions. Objective 6. Explicitly simulate microbial activity and physiology in MIcrobial-MIneral Carbon Stabilization model (MIMICS), and improve model predictions under changing environments. Here, used our newly developed MIMICS C model with coupled N cycles and data synthesis to examine how climate-change driven alterations in precipitation patterns are likely to affect N cycling and losses in agricultural landscapes and to highlight promising interventions to minimize environmental N losses while maintaining or increasing productivity. We review climate projections for Midwest U.S. region and then highlight key water-N linkages and the vulnerability of N to environmental loss. Finally, we show that conventional, fertilizer-use-efficiency-based approaches are insufficient to mitigate N losses now, and will likely be even less effective under climate change scenarios.

Publications

  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Bailey, V.L., B.B. Lamberty, K. DeAngelis, A.S. Grandy, C.V. Hawkes, K. Heckman, K. Lajtha, R.P. Phillips, B.N. Sulman, K.E.O. Todd-Brown, and M.D. Wallenstein. 2017. Soil carbon cycling proxies: understanding their critical role in understanding climate change feedbacks, Global Change Biology, 10.1111/gcb.13926
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Melillo, J.M., S.D. Frey, K.M. DeAngelis, W.J. Werner, M.J. Bernard, F.P. Bowles, G. Pold, M.A. Knorr, A.S. Grandy. 2017. Long-term Pattern and magnitude of soil carbon feedback to the climate system in a warming world., Science, 358:101-105
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Austin, E., K. Wickings, M. McDaniel, G.P. Robertson, and A.S. Grandy. 2017. Cover crop root contributions to soil carbon in a no-till corn bioenergy cropping system, Global Change Biology-Bioenergy, 9:1252-1263.
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Buchkowski, R.W., M.A. Bradford, A. S. Grandy, O.J. Schmitz, and W.R. Wieder. 2017. Applying population ecology theory to advance understanding of belowground biogeochemistry, Ecology Letters, 20:231-245.
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Pold, G., A.S. Grandy, J.M. Melillo, and K.M. DeAngelis. 2017. Changes in substrate availability drive carbon cycle response to chronic warming. Soil Biology and Biochemistry, 110:68-78.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Invited Keynote Presentation. Revising Paradigms of Nitrogen Mineralization and Availability in Agroecosystems. Soil Ecology Society, Annual Meeting, Fort Collins, CO. June 5-9, 2017
  • Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Invited Conference Panel: Soil Health Research Directions (3 participants including Kate Scow). Soil Ecology Society, Annual Meeting, Fort Collins, CO. June 5-9, 2017 Yes
  • Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Invited. Scaling soil organic matter with microbial physiology, University of Adelaide, Adelaide, Australia, 04/2017
  • Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Invited. Scaling soil organic matter with microbial physiology, University of Western Sydney, Australia, 04/2017
  • Type: Conference Papers and Presentations Status: Accepted Year Published: 2017 Citation: Invited. Soil minerals: a hidden source of rhizosphere nitrogen mediates plant-microbe competition, University of Waikato, Auckland, NZ, 3/2017
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Invited. Soil minerals: an overlooked mediator of plant-microbe competition for organic N in the rhizosphere. American Geophysical Union Fall Meeting, San Francisco, CA, 12/2016
  • Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Grandy, A. S., Jilling, A., and Keiluweit, M. Soil Minerals in the Rhizosphere: A Hidden Source of Nitrogen and Mediator of Plant Microbe Competition. Ecological Society of America, Annual meeting, Portland, OR. August 6-11, 2017.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Castle, S., Song, Z, Grandy, A. S. and Kinkel, L. Does Climate Warming Alter Plant Diversity-Soil Carbon Relationships and Associated Soil Microbial Communities? Soil Ecology Society, Annual Meeting, Fort Collins, CO. June 5-9, 2017.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: ONeil, B., &, Grandy, A. S., et. al. Linking Soil C and N Cycling and Trace Gas Flues with soil Bacterial Communities Along a Gradient of Simple to Complex Crop Rotations. Soil Ecology Society, Annual Meeting, Fort Collins, CO. June 5-9, 2017.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Daly, A., Richter, A. and Grandy, A. S. Influence of Wet-Dry Cycles and Organic Management on Gross Nitrogen Depolymerization in Agricultural Soils. Soil Ecology Society, Annual Meeting, Fort Collins, CO. June 5-9, 2017
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Tiemann, L. K., A. S. Grandy and J. Hartter. Connections between Soil Fertility Declines, Land Use, Ethnicity, Education, and Wealth in Uganda. American Geophysical Union, Annual Meeting, San Francisco, CA. December 12-16, 2016.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Kallenbach, C. M., Fierer, N., Frey, S. D., and A.S. Grandy. Mineralogy impacts microbial community establishment and early microbial-SOM formation. American Geophysical Union Conference, San Francisco, CA, 12/2016


Progress 10/01/15 to 09/30/16

Outputs
Target Audience:The target audience includes other scientists and land managers receiving information about this project from papers and presentations and students that are early career scientists training in the PI's lab or taking his classes. The research conducted in this project is incorporated into NR 797, Environmental Soil Chemistry, as well as a new couse, Soil Fertility and the Environment. My lab's work was featured in a Grain News article titled, 'Building up the soil in your fields: Changing your crop rotation and management can change the content of your soil'. It was also featured in an article in De Standaard, Belgium's largest newspaper. I was also an invited speaker at a regional cover crop conference for scientists and practitioners (~200 people)in Maryland. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Postdoctoral scientists Emily Austin, Tim Bowles,and Joerg Schnecker, and Ph.D. students Amanda Daly, Andrea Jilling, Lauren Breza,Emily Kyker-Snowman (Grandy lab PhD students) and Igor Alexandre (visiting student from Brazil for one year) and Grace Pold (visiting student from UMass Amherst for two weeks) have all participated on this project. All Grandy lab students and postdocs have attendednational or international meetings in the past year where their current research was presented, and continue developing advanced approaches to understanding soil organic matter and nitrogen dynamics. The postdocs and graduate students have been provided with teaching opportunities in my lab and classes, and all have participated in teaching classes and leading lab group meetings. Further, all have been given the opportunity to develop new collaborations with my colleagues. My lab has also provided seven undergraduate students during this period with opportunities to participate in ongoing projects. How have the results been disseminated to communities of interest?The work was shared with the scientific community in34 published papers, including an article in Nature Communications, and two additional in press at Ecology Letters and Global Change Biology - Bioenergy. We gave 15 presentations to the scientific community, which included5 invited talks at conferences or universities. We also gavean outreach presentations to stakeholder groups in Maryland on cover crops, and were featured in several popular press publications. What do you plan to do during the next reporting period to accomplish the goals?To address the role of clays and priming in SOM dynamics, we will continue to examine whether mineral-associated organic matter is accessible to microbes?.Do soluble rhizodeposits enable microbes to accessmineral-bound nitrogen- Through directly desorbing/liberating mineral-bound compounds? Through stimulating microbes that are more adept at interfering with sorptive interactions (i.e. targeted enzyme production)? Or through stimulating microbial activity to a point of N-starvation and N-desperation? Along with answering these questions, we are also examining with field and lab experiments howdoes management (tillage and cover cropping) impact the chemical composition of clay-associated SOM and/or dominant binding mechanisms? How do these impacts influence the N-priming capacity and the N-priming response more generally? We continue to also work on the nitrogen cycle and incorporate it into models. We are fine tuning a new nitrogen mineralization technique, based upon depolymerization by isotope pool dilution of 15N-labeled amino acids coupled with analysis by GC-qMS, and nitrogen mineralization (nitrification and ammonification, as well as N immobilization) by isotope pool dilution of 15N-labeled NH4+ or NO3-. The quantification of protein depolymerization using amino acid pool dilution and GC-qMS is a recently developed method, which in the last year has been undergoing development and optimization in Grandy's lab at UNH under the direction of a postdoc who helped develop the original method. We have also begun and will continue incorporating nitrogen into MIMICS.

Impacts
What was accomplished under these goals? Impact. The loss of soil organic matter from agricultural soils has severe local regional, and global consequences. Soil organic matter is intricately linked with soil health, drives nitrogen and other nutrient cycling and plant productivity, and contains twice as much carbon as the atmosphere. Restoring soil organic matter in agricultural systems is thus an essential component of sustainability, but the processes by which this is done remain uncertain. We continue to seek an understanding of where and how soil organic matter is formed, and how these processes are influenced by management. Scientists have generally considered that the best way to build soil organic matter was to slow down or inhibit decomposition using plants that soil microbes find difficult to decompose. The idea is that the undecomposed plant parts would gradually become soil organic matter, especially if the soil microbial community was inactive. However, in a recent Nature Communications paper we show that soil organic matter accumulates from inputs of dead microbial cells and microbial byproducts formed when microbes eat plant roots and residues, rather than from the plants themselves. This has been challenging for scientists to prove because once soil organic matter is formed, identifying whether it was most recently a plant or microbial cell is impossible. Soil organic matter accumulation is greatest when more-not less-active microbial biomass is formed. This is especially true when that biomass is produced more efficiently, meaning more of the substrate is converted to biomass rather than carbon dioxide. Challenging another long-held view, we also show that the characteristics of the microbial community are even more important for soil organic matter formation than soil type. The new research provides promise for designing agricultural systems that promote microbial communities that optimize soil organic matter formation. Applying these concepts, much of the historical research in agricultural systems has focused on tillage, but its effects on soil organic matter are inconsistent, and no-till cropping systems do not always build soil organic matter. We have focused on an alternative approach to restoring soil organic matter - increasing agricultural crop diversity. We continued to use principles from biodiversity-ecosystem function theory to test whether changes in plant diversity over time (e.g., through crop rotation) affect soil communities and function in an agroecosystem. Using field and lab experiments, we show that as crop diversity increases, distinctive soil microbial communities are related to increases in soil aggregation,organic carbon and total nitrogen stocks, microbial activity, accelerated rates of nutrient cycling, and the ratio of carbon to nitrogen acquiring enzyme activities. By increasing the quantity, quality and complexity of crop residues, high diversity rotations can sustain soil biological communities, with positive effects on soil organic matter accrual, soil fertility, and crop yield. Objective 1. Quantify the variation in microbial physiological traits driving Soil Organic Matter (SOM) formation in organic and conventional agricultural soils. Completed and published last reporting period, (Kallenbach, C.M.*, A.S. Grandy, S.D. Frey, and A. F. Diefendorf. Microbial physiology and necromass regulate agricultural soil carbon accumulation. 2015. Soil Biology & Biochemistry (SBB), 9:279-290 - research featured in Our Changing Planet, US Global change Research Program annual report to Congress; Top-ranked SBB paper for social media; top-ten most downloaded paper) Objective 2. Develop and apply new laboratory methods for examining plant and microbial lipids in soil organic matter. This objective has not yet begun. Objective3. Ascertain how clay mineralogy influences the direction and size of nitrogen priming effects. Objective 4. Determine how microbial community composition and activity interact with clay content and type to control priming effects. Objective 5. Determine how clay texture and mineralogy control microbial priming of mineral-associated N. Our first effort to tackle these objectives has been the development of a new conceptual framework. Recent research on the rate-limiting steps in soil nitrogen (N) availability has shifted in focus from mineralization to soil organic matter (SOM) depolymerization. To that end, Schimel and Bennett (2004) argued that together with enzymatic breakdown of polymers to monomers, microsite processes and plant-microbial competition collectively drive N cycling. Here weare developingnew conceptual models arguing that while depolymerization is a critical first step, mineral-organic associations may ultimately regulate the provisioning of bioavailable organic N, especially in the rhizosphere. Mineral-associated organic matter (MAOM) is a rich reservoir for N in soils and often holds 5-7x more N than particulate or labile fractions. However, MAOM is considered largely unavailable to plants as a source of N due to the physicochemical forces on mineral surfaces that stabilize organic matter. We argue that in rhizosphere hotspots, MAOM is in fact, a potentially mineralizable and important source of nitrogen for plants. In experimental work, we collected soils from an ongoing experiment replicated across four growing sites in north central and mid-Atlantic United States. Soils were subject to different tillage and cover crop treatments, representing a gradient from intensive to more conservation-oriented systems. Combining both sonication and wet-sieving techniques, we fractionated bulk soils into four distinct components: free Particulate Organic Matter (fPOM), occluded POM (oPOM), a coarse silt fraction, and fine silt and clay-organic matter (MAOM). We measured the weight of recovered fractions and measured the C and N content of each.Our results reveal that management significantly influenced N and C distribution across SOM fractions, however, the response was context-specific. Responses to management were not consistent between sites, possibly highlighting divergent processes underlying SOM transformation and transfer across pools at different sites. Collectively, the above work is challenging our understanding of where and how plants obtain their nitrogen and will suggest new approaches to better synchronize plant N needs and soil N availability in agricultural systems. Objective 6. Explicitly simulate microbial activity and physiology inMIcrobial-MIneral Carbon Stabilization model (MIMICS), and improve model predictions under changing environments. First, we considered the theoretical implications of introducing theory from population ecology into MIMICS and other microbial-explicit soil biogeochemistry models (Buchkowski, R.W., M.A. Bradford, A. S. Grandy, O.J. Schmitz, and W.R. Wieder. 2017 Applying population ecology theory to advance understanding of belowground biogeochemistry, Ecology Letters, 20: 231-245). Second, we developed, parameterized, and validated a coupled C and N version of MIMICS. This model accomplishes the following: Represents microbial-explicit soil C and N cycling through litter, microbial, and stabilized soil organic matter (SOM) pools; Simulates C and N losses from litterbags in the Long-Term Intersite Decomposition Experiment Team (LIDET) dataset with reasonable accuracy; 3) Performs better than existing soil models in simulating C and N losses from LIDET litterbags. These advances are now incorporated into a manuscript to be submitted in 2017. Collectively this work is improving our representation of microbial processes in models and simultaneously improving predictions of global biogeochemical processes and their response to human activities.

Publications

  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Kallenbach, C.M., S.D. Frey and A.S. Grandy. Direct evidence for microbial-derived soil organic matter formation and its ecophysiological controls, Nature Communications, 7:13630
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Buchkowski, R.W., M.A. Bradford, A. S. Grandy, O.J. Schmitz, and W.R. Wieder.2017 Applying population ecology theory to advance understanding of belowground biogeochemistry, Ecology Letters, 20: 231-245 DOI: 10.1111/ele.12712
  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Austin, E., K. Wickings, M. McDaniel, G.P. Robertson, and A.S. Grandy, Cover crop root contributions to soil carbon in a no-till corn bioenergy cropping system, Global Change Biology-Bioenergy, DOI: 10.1111/gcbb.12428
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Grandy, A.S., W.R. Wieder, K. Wickings, and E. Kyker-Snowman. 2016 Beyond microbes: Are fauna the next frontier in soil biogeochemical models? Soil Biology and Biochemistry, 102:40-44
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: McDaniel, M.D. and A.S. Grandy. 2016. Soil microbial biomass and function are altered by 12 years of crop rotation. SOIL, 2:583-599.
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Hurisso, T.T. S.W. Culman, W.R. Horwath, J. Wade, D. Cass, J.W. Beniston, T.M. Bowles, A.S. Grandy, A.J. Franzluebbers, M.E. Schipanski, Lucas, C. Ugarte. 2016. Comparison of permanganate oxidizable C and mineralizable C for assessment of organic matter stabilization and mineralization, Soil Science Society of America Journal, 80:1352-1364
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: McDaniel, M.D., A.S. Grandy, L.K. Tiemann, and M.N. Weintraub. 2016. Eleven years of crop diversification alters decomposition dynamics of litter mixtures, Ecosphere, 7:1-18
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Castle, S.C., D.R. Nemergut, A.S. Grandy, J.W. Leff, E.B. Graham, E. Hood, S.K. Schmidt, K. Wickings, C.C. Cleveland. 2016. Successional processes drive convergence of microbial communities, Soil Biology and Biochemistry, Soil Biology and Biochemistry, 101, 74-84.
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Geyer, K.M., E. Kyker-Snowman, A.S. Grandy, and S.D. Frey. Microbial efficiency: Accounting for physiological, ecological, and time-dependent controls over the fate of metabolized organic matter, Biogeochemistry,127:173-188
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Rinkes, Z.L., I. Bertrand, B.H.Z. Amin, A.S. Grandy, K. Wickings, and M.N. Weintraub. Nitrogen alters microbial enzyme dynamics but not lignin chemistry during maize decomposition, Biogeochemistry, 128:171-186
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Williams, A., A.S. Davis, P.M. Ewing, M. Li, Y. Lou, A.S. Davis, A.S. Grandy, D.A. Kane, R.T. Koide, D.A. Mortensen, R.G. Smith, S.S. Snapp, K.A. Spokas, A.C. Yannerell, N.R. Jordan. Precision management of soil nitrogen via functional zone management. Agriculture, Ecosystems & Environment, 231: 291-295
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Williams, A., D.A. Kane, P.M. Ewing, L.W. Atwood, A. Jilling, M. Li, Y. Lou, A.S. Davis, A.S. Grandy, S.C. Huerd, M.C. Hunter, R.T. Koide, D.A. Mortensen, R.G. Smith, S.S. Snapp, K.A. Spokas, A.C. Yannarell, and N.R. Jordan. Soil functional zone management: a vehicle for enhancing production and soil ecosystem services in row-crop agroecosystems, Frontiers in Plant Science, 7:65.
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Wickings, K.W., A.S. Grandy, and A.N. Kravchenko. 2016. Going with the flow: landscape position drives differences in microbial biomass and activity in conventional, low input, and organic agricultural systems in the Midwestern U.S., Agriculture Ecosystems and Environment, 218:1-10
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Diem, J.E., J. Hartter, J.D. Salerno, E. McIntyre, and A.S. Grandy. 2016. Comparison of measured multi-decadal rainfall variability with farmers perceptions of and responses to seasonal changes in western Uganda, Regional Environmental Change, DOI:10.1007/s10113-016-0943-1.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Soil minerals: an overlooked mediator of plant-microbe competition for organic N in the rhizosphere. American Geophysical Union Fall Meeting, San Francisco, CA, 12/2016
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Microbial-driven soil organic matter formation, Cornell University Biogeochemistry Seminar Series, Ithaca, NY, 10/16.
  • Type: Other Status: Other Year Published: 2016 Citation: Crop Biodiversity: The key to improving Soil Ecosystem Function, Colorado State University, Fort Collins, CO, 06/2016.
  • Type: Other Status: Other Year Published: 2016 Citation: Scaling Soil Organic Matter Dynamics, Colorado State University Fort Collins, CO, 06/2016.
  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Williams, A., A.S. Davis, A. Jilling. A.S. Grandy, R.T. Koide, D.A. Mortensen, R.G. Smith, S.S. Snapp, K.A. Spokas, A.C. Yannerell, N.R. Jordan. 2016. Reconcing opposing soil processes in row-crop agroecosystems via soil functional zone management. Agriculture, Ecosystems & Environment, 236:99-107.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Tiemann, L. K., A. S. Grandy and J. Hartter. Connections between Soil Fertility Declines, Land Use, Ethnicity, Education, and Wealth in Uganda. American Geophysical Union, Annual Meeting, San Francisco, CA. December 12-16, 2016.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Kallenbach, C. M., Fierer, N., Frey, S. D., and A.S. Grandy. Mineralogy impacts microbial community establishment and early microbial-SOM formation. American Geophysical Union Conference, San Francisco, CA, 12/2016
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Bowles, T.M., and Grandy, A.S. Addressing agricultural nitrogen losses in a changing climate. Soil Science Society of America Annual Meeting, Phoenix, AZ. 11/2016
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Schnecker ,J, and A.S. Grandy. Microbial foraging strategy is dependent on substrate concentration. SOMmic  Microbial Contribution and Impact in Soil Organic Matter, Structure and Genesis Workshop, Leipzig, Germany, 11/2016
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Jilling, A. and A.S. Grandy. Clay minerals: Critical mediators of nitrogen availability in the rhizosphere. SOMMIC Workshop: Microbial Contribution and Impact on Soil Organic Matter, Structure, and Genesis, Leipzig, Germany, 11/2016.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Schnecker, J., A. S. Grandy, D.B. Meeden, F. Calderon, M. Cavigelli, M. Lehman, and L. Tieman. Does crop rotational diversity increase soil microbial resistance and resilience to drought and flooding? Ecological Society of America Annual Meeting, Fort Lauderdale, Fl, 08/2016
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Schnecker,J, and A.S. Grandy. Soil organic matter content: a non-liner control on microbial respiration in soils. European Geoscience Union General Assembly, Vienna, Austria, 04/2016
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Grandy, A.S. Temporal plant diversity and intensification drives microbial communities and soil carbon dynamics in agricultural systems. Soil Ecology Society Biennial Meeting, Colorado Springs, CO, 06/2015
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Jilling, A. and A.S. Grandy. Nitrogen distribution across organic matter fractions varies with soil type and management. Graduate Research Conference, University of New Hampshire, 4/2016.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Austin, EE, Wickings, K, McDaniel M, Robertson, PG, Grandy, AS. 2016. The fate of cover crop root and shoot carbon belowground in a corn bioenergy system. American Geophysical Union annual fall meeting, San Francisco, CA.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Daly, A.B., A.S. Grandy. How agricultural management shapes soil microbial communities: patterns emerging from genetic and genomic studies. European Geological Union Annual Meeting, Vienna, Austria, 04/2016