Source: UTAH STATE UNIVERSITY submitted to NRP
MICROBIAL CARBON-USE EFFICIENCY IN AGROECOSYSTEMS: THE EFFECT OF DROUGHT AND N AVAILABILITY ON SOIL MICROBIAL PRODUCTION AND RESPIRATION
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
AFRI COMPETITIVE GRANT
Reporting Frequency
Annual
Accession No.
1008845
Grant No.
2016-67004-24920
Cumulative Award Amt.
$714,080.00
Proposal No.
2015-08406
Multistate No.
(N/A)
Project Start Date
Feb 15, 2016
Project End Date
Feb 14, 2021
Grant Year
2016
Program Code
[A3143]- Climate and Microbial Processes in Agroecosystems
Recipient Organization
UTAH STATE UNIVERSITY
(N/A)
LOGAN,UT 84322
Performing Department
(N/A)
Non Technical Summary
Current biogeochemical models predicting carbon sequestration rates in soils are very sensitive to changes in the efficiency at which soil microbes utilize organic matter. Changes in the proportion of organic matter that is released as carbon dioxide rather than incorporated into microbial biomass can have profound effects on model predictions. This project will examine how drought intensity and frequency, as well as the availability of inorganic nutrients such as nitrogen influence microbial efficiencies. We will develop equations describing these effects that can be incorporated into ecosystem models to improve predictions of how climate change will influence carbon sequestration in soils of agroecosystems.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
10201101070100%
Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships;

Subject Of Investigation
0110 - Soil;

Field Of Science
1070 - Ecology;
Goals / Objectives
The overall goal of this study is to quantitatively characterize the relationship between soil moisture, substrate supply, and microbial carbon-use efficieny (CUE) so that biogeochemical models can better predict the effects of drought on C sequestration and CO2 emissions in agroecosystems. Our primary research objectives are to:1) Determine whether CUE in undisturbed plant-soil systems differs from estimates based on disturbed, sieved soils;2) Determine the relative effects of C- versus N-limitations on CUE; and3) Determine how CUE changes with soil moisture, and the relative importance of the two mechanisms for soil moisture effects: i) diffusional limitations to substrate supply vs ii) direct physiological effects of water stress on microbial metabolism.
Project Methods
We will examine the effect of C and N substrate supply and soil moisture on microbial C-use efficiency (CUE) in three agroecosystems: 1) Irrigated pasture consisting of either Birdsfoot trefoil (BFT) or meadow brome . These pasture types are part of a larger study in the Cache Valley of Northern Utah to examine the feasibility and impact on C-footprints of keeping beef-finishing operations at individual local private ranches and shifting away from finishing at commercial feedlots. 2) Tilled cropland (continuous corn silage) receiving inorganic amendments and composted steer manure. These plots are part of an ongoing cropland field experiment in Cache Valley examining the effect of contrasting nitrogen sources on the microbial communities responsible for mineralization and nitrification; and 3) Grazed Sagebrush bunchgrass rangeland. This site is located SE of Bear Lake, UT, where we have previously performed research examining controls on trace-gas emissions, C and N-cycling rates, and the effect of hydraulic-lift by sagebrush plants on microbial C and N-cycling processes.At all sites, soil microbial CUE will be measured in undisturbed field soils at least four times during the growing season (early June, July, Aug, & Sep). Sampling times will include dates during springtime or during summer immediately following irrigation when soil moisture is at or near field capacity and plant and microbial activity is rapid, and during the summer immediately prior to irrigation when surface soils are drier. Measurements will be made by inserting a segment of PVC pipe (10-cm long, 25-cm diam.), 1.5 cm into the mineral soil surface. We will inject 15N- and 13C-labeled substrates as solutions (NH4+, glucose, acetate) and as gas (NH3, acetic acid) during spring and as gas during summer; see below) into four marked locations in the mineral soil within the PVC ring. Immediately after injecting substrates, a PVC cover will be placed over the top of the ring for 12- to 96-h incubations. During these incubations, 13CO2 production from the intact soils will be measured by cavity ring-down spectroscopy using a Picarro 2131-i analyzer. After incubation, soil cores (4.8 x 10 cm) will be collected from the four marked injection locations and subsamples immediately extracted in 0.5 M K2SO4 for analysis of extractable-organic 13C, 15NH4+, and 15NO3-. Samples will also be immediately chloroform-fumigated in the field for determination of microbial biomass 13C and 15N. The remaining soil sample will be placed in an ice chest and returned to the lab for analyses of gravimetric soil moisture content, soil organic 13C and 15N, and 13C-PLFA. Microbial assimilation (and CUE) will be estimated based on the quantity of labeled C and N in K2SO4 extractable and non-extractable soil pools.Gas Injection Method: For N additions, 15NH3 gas (99 at% 15N, diluted with air to 10 mmol NH3 L-1) will be injected into soil using a nylon syringe and 15-cm long 18-guage double side-port needle. Sufficient NH3 (typically 3--12 mL) will be injected to increase the soil NH4+ pool by 50% for N assimilation measurements, or more for greater stimulation of NH4+ supply.. For injections of 13C-acetic acid vapor, a different injection system is used. This system consists of a small battery operated air pump that forces air (120 mL min-1) through two glass columns (in series) containing glass beads coated with 13C-acetic acid. The columns are connected by Tygon tubing to a 15-cm long double side-port needle, which is used to inject the vapor into the top 10-cm of mineral soil. Injections of different duration can be used to deliver different quantities of 13C-acetic acid into the soil solution.The effect of C versus N limitation on CUE will be evaluated during year-1 at the pasture site by manipulating short-term N and C availability in the N-fixing BFT plots, and fertilized and unfertilized subplots of the meadow brome plots. For this experiment, two different amounts of 15NH4+ and four different amounts of each 13C-substrate will be injected into intact soil as described previously (solutions of NH4+ and glucose or acetate in spring, and NH3 and acetic acid gas in summer).Mixed Soil Experiments: Soil samples (n=5) from each field site will be brought back to the laboratory for more controlled measurements of the kinetics of 13C and 15N assimilation, respiration, and CUE over time scales ranging from 1 h to 1 month at different moisture contents and with different 13C substrates. We will also determine rates of microbial turnover. In addition, we will examine the effect of successive pulses of C, the effect of different C substrates (glucose, acetate, amino acids), and NH4+ versus NO3- additions on C and N assimilation rates, respiration, and CUE in soils from the three agroecosystems.During the summer at all field sites, we will examine the effects of soil moisture on CUE in undisturbed field soils, as well as in lab assays of mixed soil to determine if declines in soil moisture limit microbial growth and respiration through its effects on substrate supply (i.e. low water content limits diffusion rates) or through its effect on microbial metabolism (i.e. low water potential inhibits enzyme activity and causes specific-ion toxicities). Microbial growth, storage, respiration, and CUE will be measured using the 13C-acetic acid and 15NH3 gas injection techniques and using solutions of 15NH4+ and 13C- acetate. Three treatments (two amounts of gas injections to measure rates under ambient soil moisture conditions, and one solution injection to measure rates at high moisture) will be applied to undisturbed soils at each site in a randomized block design (five blocks. With this treatment we will determine rates under ambient conditions (diffusional limitations to substrate supply and physiological constraints on activity due to low water potential). In the second treatment, gas injections will be used to provide 120% of max. microbial demand through the gas phase, bypassing diffusional limitations, and leaving only the physiological constraints. In the third treatment, injections of solutions containing 120% of max. microbial C and N demand will be added with sufficient water to increase the soil moisture content to field capacity. We will use differences among the three treatments to determine the degree to which water content vs water potential (i.e. diffusional vs physiological limitations) limit microbial growth, respiration, and CUE in undisturbed soils at the two different soil moisture contents.In concert with field work during the summer, we will examine the interactive effects of soil moisture and substrate supply on growth and CUE using lab assays of sieved (<2 mm) soils from the sites. Soils will be wet to six different water potentials ranging from -3 to -0.03 MPa and then exposed to three different concentrations of 13C acetic acid vapor or 15NH3 during 12-h assays. Microbial respiration and incorporation of 13C and 15N during these assays will be compared to rates in shaken soil slurries where water potential is controlled across the same range (-3 to -0.03 MPa) by varying mixtures of inorganic salt concentrations. In the slurries, diffusional limitations to substrate supply are eliminated, and thus declines in activity at low water potential can be entirely attributed to adverse physiological effects. In our slurries, the composition of the salt mixture will be determined using a soil chemical equilibrium model that predicts changes in the ionic composition of the soil solution at different water potentials due to cation-exchange and precipitation reactions. This experiment will allow us to partition the effects of soil moisture on microbial activity and CUE into the effects due to physiological desiccation stress vs diffusional limitations. Our design will also allow us to determine if C or N is more limiting to growth at different soil water contents.

Progress 02/15/16 to 02/14/21

Outputs
Target Audience:soil microbiologists, soil ecologists, biogeochemists, earth system modelers Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?During the course of this project, a post-doctoral researcher (female), a visiting scientist (female), and a PhD student (female) were trained in research techniques (including experimental design, stable isotope techniques, molecular analyses of microbial community structure, PLFA extraction and analysis, and nutrient analysis), oral and written communication (including oral presentation of research results at national meetings and publication writing), and supervisory skills (supervision of undergraduate lab assistants). Two lab technicians (both female, originally undergraduate students in the lab) were trained in analytical techniques, and operated and maintained the isotope-ratio mass spectrometer, flow-injection autoanalyzer, and cavity ring-down spectrometer in the lab. They also supervised the undergraduate lab assistants. Four undergraduate students (one female) and one high school student (female, Hispanic) were trained in laboratory techniques (cleanliness, weighing and sample preparation). The high school student was part of an effort initiated in the Biology Department at USU by the PD (Stark) to acclimate "at risk" minority students to the university research environment. With the aid of science teachers from the local high school, four such students were identified and offered paid positions as lab assistants in Department research labs. The overall goal was to "de-mystify" the university environment and make these students comfortable coming to the university, and to cultivate an interest in the research so that the students would consider applying for admittance to a college or university. The effort was highly successful, in that all four students applied for admission to USU. How have the results been disseminated to communities of interest?Numerous oral and poster presentations have been given at national conferences. At least five papers will be/have been published in peer-reviewed journals that will reach the intended scientific audience. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? During this project, we examined the mechanisms by which soil moisture and other factors regulate microbial carbon-use efficiency (CUE). Microbial CUE is the efficiency at which microbes assimilate detrital carbon (C) into microbial biomass rather than releasing it as carbon dioxide (CO2) during decomposition. It is a variable that is extremely important in determining how much plant C becomes sequestered into soil organic matter versus how much is lost to the atmosphere during respiration. This variable also regulates microbial immobilization of nutrients such as nitrogen (N), phosphorus (P), sulfur (S), etc. and thus, controls the availability of these nutrients to plants. Ecosystem and earth system models attempting to predict C sequestration rates in soils (or nutrient availabilities to plants) are extremely sensitive to changes in CUE; small changes can result in an ecosystem shifting from a source of CO2 to a sink for CO2. While a few studies have examined how increases in temperatures influence CUE, no study has examined how changes in soil moisture will impact CUE. This is a huge knowledge gap, given that climate models predict that drought frequency and intensity will increase in many regions, and given that soil microbial activity is even more strongly affected by changes in soil moisture than by changes in temperature. Soil moisture affects microbial activity by two mechanisms: 1) soil water potential regulates microbial desiccation effects (enzyme dehydration and specific-ion toxicities) which influence microbial physiological potential, and 2) soil water content regulates the rate at which substrates diffuse to microbial cells, and thus regulates the substrate supply. These two factors interact to control rates of microbial activity, and since the two factors have different effects on microbial assimilation and respiration, they may have different effects on CUE. Soils with different textures have different water potential--water content relationships, and thus the effect of soil moisture on CUE may not be the same in say, a clay loam soil as in a sandy loam soil. To accurately model the effect of soil moisture on CUE across a wide range of soil types, we must understand the separate effects of soil water potential and water content on both microbial assimilation and respiration. The primary objective of our study was to determine how CUE changes with soil moisture, and the relative importance of the two mechanisms for soil moisture effects: i) diffusional limitations to substrate supply vs ii) direct physiological effects of water stress on microbial metabolism. Secondary objectives were to determine how C vs N limitations influence CUE, and whether or not CUE measured in disturbed samples represents CUE in undisturbed plant soil systems. We met the primary objective by separating the effects of water potential and content on microbial assimilation, respiration, and CUE by comparing rates in moist-to-dry soil (where microbes are subjected to both desiccation and substrate supply limitations) to soils incubated in shaken soil slurries where water potentials were adjusted using mixtures of salts designed to mimic the composition of the thin water films surrounding soil microbes at different water contents. Thus, in these slurries, microbes are subject to the desiccating conditions without the substrate limitation. By difference, we were able to partition the separate effects of water potential from water content. This work, which we reported in Butcher et al. (2020), showed that in a sandy loam soil, neither microbial respiration, C assimilation, nor CUE were strongly affected by the direct physiological effects of low water potential in the shaken soil slurries. In contrast, all three microbial variables declined exponentially with decreases in water content. This work demonstrated that, at least in this one soil, lower soil moisture exerts its influence on microbial metabolism almost entirely by reducing diffusion of substrates to soil microbes. In a second paper (Nasto et al., in prep), we report results where we applied this same approach to four different soils with a wide range of clay and sand contents, to see if the same mechanisms operated over a wide range of textures. While the soils showed widely different microbial respiration, assimilation, and CUE, the responses to water potential and water content were essentially the same, such that CUE was a function of water content, not water potential. These conclusions have important implications for biogeochemical models: the extremely important variable, CUE, can be predicted in models using the simple to measure soil water content, rather than the more difficult to measure, water potential. Since soil water content is much easier to predict and measure, the impacts of changes in soil moisture in CUE can be much more readily incorporated into biogeochemical models. The secondary objectives, examining the interactions of C and N availabilities on CUE, and CUE in intact plant soil systems, were addressed at three different field sites in the Intermountain western US, where we focused on the role of exotic plant invaders common in sagebrush ecosystems in modifying C supply (quantity and quality of plant litter inputs) to microbes. We examined how differences in C supply from the plants influenced microbial CUE, and the resulting feedback effects on N release by microbes and plant uptake and growth. This work is reported in two papers, Nasto et al. (accepted), Morris et al. (submitted). In the first paper we showed that in field plots, four exotic invasive species (cheatgrass, leafy spurge, spotted knapweed, and sulfur cinquefoil) all released organic substrates that lowered soil microbial CUE relative to adjacent native plant communities. This lower CUE resulted in greater release of plant available N, which the exotics were able to exploit to maintain plant community dominance relative to native grasses. At a second set of field plots examining differences among cheatgrass, crested wheatgrass (an introduced exotic), and native stands of sagebrush, however, (Morris et al. submitted), the results were somewhat different. In these plots the impact of the vegetation in modifying soil moisture regimes (rather than organic inputs) dominated N-cycling effects. Overall, we conclude that an important mechanism by which invasive plant species create stable plant communities is by creating stimulated nutrient regimes, which they are able to exploit. However, they may create these changes in nutrient availability either by providing different organic substrates to microbes or by modifying soil moisture--both of which impact microbial CUE and nutrient release.

Publications

  • Type: Journal Articles Status: Published Year Published: 2016 Citation: Morris, Kendalynn A., John M. Stark, Bruce Bugbee, Jeanette M. Norton. 2016. The invasive annual cheatgrass releases more nitrogen than crested wheatgrass through root exudation and senescence. Oecologia 181(4): 971-983. DOI 10.1007/s00442-015-3544-7. Published in the Highlighted Student Paper - Original Research category.
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: Butcher, Kirsten R., Megan K. Nasto, Jeanette M. Norton, John M. Stark. 2020. Physical mechanisms for soil moisture effects on microbial carbon-use efficiency in a sandy loam soil in the Western United States. Soil Biology & Biochemistry 150:107969
  • Type: Journal Articles Status: Accepted Year Published: 2022 Citation: Nasto, Megan K., Morgan L. McLeod, Lorinda Bullingham, Ylva Lekberg, John M. Stark. Accepted. The effect of plant invasion on soil microbial carbon-use efficiency in semiarid grasslands of the Rocky Mountain West. J. Ecology
  • Type: Journal Articles Status: Submitted Year Published: 2022 Citation: Morris, Kendalynn A., Peter Saetre, Urszula Norton, John M. Stark. Submitted. Soil moisture and plant community effects on nitrogen cycling in a semi-arid ecosystem. Biogeochemistry.
  • Type: Journal Articles Status: Other Year Published: 2023 Citation: Nasto, Megan K., Kirsten R. Butcher, Jeanette M. Norton, John M. Stark. In prep. Soil moisture regulates microbial carbon-use efficiency across soil textures. Global Change Biology
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Stark, J.M. 2016. Soil Microbial Carbon-use Efficiency: Effects of Soil Moisture, Substrate Addition, and Incubation Time. Poster presentation. Ecological Society of America, 8/2016, Ft Lauderdale, FL
  • Type: Conference Papers and Presentations Status: Other Year Published: 2016 Citation: Stark, J.M., J Norton, J MacAdam. Microbial carbon-use efficiency in agroecosystems: The effects of drought and N availability on soil microbial production and respiration. Oral presentation. USDA-NIFA Project Directors meeting, 12/14/2016, San Francisco.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Stark, J.M., J Norton, J MacAdam, MK Nasto*, KB Butcher. Microbial carbon-use efficiency in agroecosystems: The effects of drought and N availability on soil microbial production and respiration. Oral presentation. USDA-NIFA Project Directors meeting, 10/22/2017, Tampa, FL. *Presenter.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2018 Citation: Nasto, M.K., and J.M. Stark. The effects of soil moisture on microbial carbon-use efficiency across soil textures. Oral presentation. Ecological Society of America, 8/2018, New Orleans, LA.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2018 Citation: Stark, J.M., M.K. Nasto. Soil moisture regulates microbial carbon-use efficiency. Oral presentation. USDA-NIFA Project Directors meeting, 12/07/2018, Washington DC.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2018 Citation: Watts, Clayton, M.K. Nasto, J.M. Stark. A test of a new extraction method for measuring soil microbial biomass carbon. USU Dept. of Biology Undergraduate Research Symposium. November 28, 2018.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2019 Citation: Butcher, Kirsten R., John M. Stark, Jennifer MacAdam, Megan K. Nasto. Mechanisms for soil moisture effects on microbial carbon-use efficiency. Oral presentation. Intermountain Branch Meeting of the American Society for Microbiology. 4/13/2019, Brigham Young University, Provo, UT.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2019 Citation: Butcher, Kirsten R., Megan K. Nasto, Jeanette M. Norton, John M. Stark. Soil moisture regulates microbial carbon-use efficiency. Oral presentation. Soil Science Society of America International Meetings. 11/10-13/2019, San Antonio, TX
  • Type: Conference Papers and Presentations Status: Other Year Published: 2019 Citation: Stark, J.M., Megan K. Nasto, Kirsten R. Butcher, Jeanette M. Norton. Soil moisture regulates microbial carbon-use efficiency in soils of different textures. Oral presentation. American Geophysical Union Meetings, 12/7/2019, San Francisco, CA.


Progress 02/15/19 to 02/14/20

Outputs
Target Audience:Soil scientists, ecosystem modelers, biogeochemists, ecologists Changes/Problems:As mentioned previously, malfunctioning of the isotope-ratio mass spectrometer has delayed many isotope analyses of soil and solution samples. We expect to upgrade the system within the next several months to fix this problem. What opportunities for training and professional development has the project provided?This year, after serving on the project for 1.75 years of the 2-y contract, the post-doctoral researcher (Megan Nasto) obtained a permanent, professional position as a Senior Technical Analyst for the Utah Forest Institute at Utah State University Dept. of Wildland Resources. The PhD student (Kirsten Butcher) completed her coursework and is now focusing on her dissertation research, which is centered on this project. She attended two conferences, where she presented her research results. How have the results been disseminated to communities of interest?Research results were presented at three conferences: Butcher, Kirsten R., John M. Stark, Jennifer MacAdam, Megan K. Nasto. Mechanisms for soil moisture effects on microbial carbon-use efficiency. Oral presentation. Intermountain Branch Meeting of the American Society for Microbiology. 4/13/2019, Brigham Young University, Provo, UT; Butcher, Kirsten R., Megan K. Nasto, Jeanette M. Norton, John M. Stark. Soil moisture regulates microbial carbon-use efficiency. Oral presentation. Soil Science Society of America International Meetings. 11/10-13/2019, San Antonio, TX; and Stark, J.M., Megan K. Nasto, Kirsten R. Butcher, Jeanette M. Norton. Soil moisture regulates microbial carbon-use efficiency in soils of different textures. Oral presentation. American Geophysical Union Meetings, 12/7/2019, San Francisco, CA. In addition, three manuscripts were prepared for submission to peer-reviewed journals: Nasto, Megan K., Kirsten R. Butcher, Jeanette M. Norton, John M. Stark. In prep. Soil moisture regulates microbial carbon-use efficiency across soil textures. For Global Change Biology, and Nasto, Megan K., Morgan L. McLeod, Lorinda Bullingham, Ylva Lekberg, John M. Stark. In prep. The effect of plant invasion on soil microbial carbon-use efficiency in semiarid grasslands of the Rocky Mountain West. The third was just recently submitted: Butcher, Kirsten R., Megan K. Nasto, Jeanette M. Norton, John M. Stark. Submitted. Mechanisms for soil moisture effects on microbial carbon-use efficiency. Soil Biology & Biochemistry. What do you plan to do during the next reporting period to accomplish the goals?We are applying for a second no-cost extension to cover the time needed for the last of the isotope analyses after we complete the upgrade of the isotope-ratio mass spectrometer. After the upgrade is made, we will complete isotope (13C and 15N) analyses of the remaining soil and solution samples. Then we will continue with data analyses and manuscript writing.

Impacts
What was accomplished under these goals? This year, activities were focused on finishing sample processing and analyses, data analyses, and writing manuscripts for publication. Previously isotopic analysis of soil samples had been inhibited because our isotope ratio mass spectrometer was malfunctioning due to communication problems. These problems were fixed during spring, and subsequently, we made considerable progress on sample processing and analysis during the next few months. Unfortunately, additional electronics problems arose that turned out to be more serious. In close succession, two of the circuit boards malfunctioned. Because of its age, the manufacturer no longer supports the electronics configuration of our Europa Scientific mass spectrometer. They were able to supply one circuit board but the second was no longer available. We are currently attempting to obtain supplemental funds to fully upgrade the electronics/communications system. This upgrade will cost approximately $47,000. In the meantime, we continued data analyses and manuscript writing, and dissemination activities. We currently have produced drafts of three manuscripts based on research from this project: one has just been submitted to Soil Biology & Biochemistry, and we expect that the other two will be ready to submit for publication within the next three months. This year we also presented research results at three national meetings: The PhD student (K. Butcher) made two of these presentations and the PI (J. Stark) gave the third presentation (see details below).

Publications

  • Type: Conference Papers and Presentations Status: Other Year Published: 2019 Citation: Presentations Stark, J. M. (Presenter & Author), Nasto, M. K., Butcher, K. R., Norton, J. M., American Geophysical Union Meetings, "Soil moisture regulates microbial carbon-use efficiency in soils of different textures," American Geophysical Union, San Francisco, CA. (December 7, 2019 - Present)
  • Type: Conference Papers and Presentations Status: Other Year Published: 2019 Citation: Presentations Butcher, K. R. (Presenter & Author), Nasto, M. K., Norton, J. M., Stark, J. M., Soil Science Society of America International Meetings, "Soil moisture regulates microbial carbon-use efficiency," Soil Science Society of America, San Antonio, TX. (November 10, 2019 - Present)
  • Type: Conference Papers and Presentations Status: Other Year Published: 2019 Citation: Presentations Butcher, K. R. (Presenter & Author), Stark, J. M. (Author Only), MacAdam, J. W., Nasto, M. K., Branch Meeting of the American Society for Microbiology, "Mechanisms for soil moisture effects on microbial carbon-use efficiency," American Society for Microbiology, Provo, UT. (April 13, 2019 - Present)


Progress 02/15/18 to 02/14/19

Outputs
Target Audience:Soil scientists, ecosystem modelers, biogeochemists, ecologists Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?A post-doc gained experience both performing research and mentoring an undergraduate student on a research project. The undergraduate student received training in experimental design, methods, and data analysis. A PhD student gained experience in experimental design, methods, and data analysis. A second undergraduate student was trained in sample preparation and use of some of the analytical equipment. A high school student (female, Hispanic) was hired to work in the lab with the goal of de-mystifying the university environment to at-risk students, giving her work experience in a research laboratory, and hopefully increasing the odds that she will eventually attend college and receive a college degree. How have the results been disseminated to communities of interest?This year, two oral presentations were given to scientific audiences. The post-doc presented a paper on the effect of soil moisture on CUE at the Ecological Society Meetings in New Orleans in August, and the PD presented these results at the USDA-NIFA Project Directors' Meeting in Washington DC in December. What do you plan to do during the next reporting period to accomplish the goals?We will continue with the remaining sample processing and analyses, and the data processing and statistical analyses. Subsequently, we will present seminars at at least two national meetings, and prepare manuscripts for submission to scientific journals. A 1-y no-cost extension is being requested for this project.

Impacts
What was accomplished under these goals? The primary goals of this project were to: 1) Determine whether CUE in undisturbed plant-soil systems differs from estimates based on disturbed, sieved soils; 2) Determine the relative effects of C- versus N-limitations on CUE; and 3) Determine how CUE changes with soil moisture, and to partition the effects into those caused by water content (diffusional limitations to substrate supply) and water potential (direct physiological effects of water stress on microbial metabolism). Accomplishments are listed by goal: 1) CUE in undisturbed plant-soil systems: Field and lab experiments measuring microbial C and N assimilation, respiration, and CUE have been completed using the field plots containing either birdsfoot trefoil or meadow brome grass. In the meadow brome grass plots, measurements were made in both fertilized (50 kg N/ha) and unfertilized subplots. Respiration measurements have been completed and analyzed. Soil samples collected during these measurements continue to be analyzed for 13C and 15N so that microbial assimilation and CUE can be determined. 2) C- versus N-limitations on CUE: Microbial communities in soils from the birdsfoot trefoil plots are C-limited rather than N limited; thus we performed lab experiments where different quantities of C-substrates (glucose and acetate) were added to alleviate the C limitation and cause a shift to N limitations. All of the samples have been processed, and data analysis is underway. 3) Effect of soil moisture on CUE, and water content versus water potential effects: Because soil textures differ in their water content/water potential relationships, separating the effects of soil water content from the effects of water potential will allow us to predict soil effects on CUE across a wide range of textures. This will greatly enhance the ability of earth system models to predict the effects of drought on C-cycling at coarse geographic scales. We used soils of four different textures in a lab experiment comparing microbial assimilation, respiration, and CUE in shaken soil slurries, where water potential was controlled using mixed salt solutions that mimicked conditions in dry soils, with incubations of sieved soil wet to water contents ranging from 5% to 20% (which produced the same range of water potentials in slurries). All samples have been processed and much of the data analysis has been completed. Preliminary results show that declining water content and water potential both reduce rates of C and N assimilation and respiration; however, declining water potential has similar effects on both assimilation and respiration, and thus CUE is unaffected by water potential. In contrast, declining water content adversely effects assimilation rates more than respiration, and thus CUE declines strongly with lower soil water content. These results imply that rates of substrate supply to microbes have a much stronger impact on CUE than do the adverse physiological effects caused by low water potential. These results also suggest that it may be possible to predict CUE in soils of a wide range of textures based on the more easily measured variable, water content, without having to know water content/potential relationships for each soil type. Additional data analyses and modeling are necessary to confirm this finding and to further define the mathematical relationships that could be used to modify earth systems models to include the effects of soil moisture (and drought) on CUE, soil C-cycling, and rates of C-sequestration.

Publications


    Progress 02/15/17 to 02/14/18

    Outputs
    Target Audience:Soil scientists, ecosystem modelers, biogeochemists Changes/Problems:None What opportunities for training and professional development has the project provided?The Post-doc attended a grant-writing workshop sponsored by Utah State University VP for Research Office. The PhD student has been taking graduate level courses at Utah State University. Bot Post-doc and PhD student were trained in techniques for extracting microbial phospholipids (PLFA) by a visiting scientist from Spain. Two undergraduate students have been trained in lab safety and analytical techniques. How have the results been disseminated to communities of interest?The Post-doc presented preliminary results from the project at the USDA-AFRI Project Directors meeting in October in Tampa FL. PD Stark presented results during an invited seminar in October to the Graduate Group in Quantitative and Systems Biology at the University of California, Merced. What do you plan to do during the next reporting period to accomplish the goals?This third year, we will complete processing and analyzing samples generated from the first two experiments. We will initiate two more laboratory experiments examining CUE in C-limited vs N-limited soils, and we will initiate a field experiment examining CUE in intact field soils supporting either bird's foot trefoil or perennial bromegrass. We will complete data analyses for the first two experiments, and then write papers for publication in peer-reviewed journals. We also expect to present the results at national meetings such as the Ecological Society of America, Agronomy Society of America, or the American Geophysical Union.

    Impacts
    What was accomplished under these goals? During the second year we re-advertised for a post-doc and successfully recruited a highly qualified individual, who began in July 2017. She spent the first couple of months becoming familiar with the project and laboratory techniques and has initiated a lab study examining how microbial C-use efficiencies (CUE) change with soil moisture in sagebrush soils with different soil textures. These experiments are designed to allow us to identify different functions for describing the effects of water potential and water content on both microbial growth and microbial respiration, and to test to see if use of the separate functions allow accurate modeling of soil moisture--CUE relationships in soils with different water holding capacities. The PhD student on the project has completed a lab experiment using soils from the irrigated permanent pasture (bird's foot trefoil), to examine the interaction between CUE and soil moisture at different microbial C and N substrate availabilities. We are currently processing the samples produced from this experiment for chemical and isotopic analyses. The PhD student and the post-doc also spent a substantial amount of time in methods development: They explored the possibilities of connecting our new Picarro 13CO2 analyzer to a total dissolved C analyzer at USU. This capability will allow us to determine 13C concentrations in water samples and soil extracts (we are currently sending samples to UC Davis for analyses at a high cost). We had moderate success with this endeavor: We found that we could measure 13C in soil extracts if the 13C was greater than 10 atom % 13C. It appears that we may be able to measure lower enrichments if the concentrations of total C can be increased in extracts. Current experiments are aimed at finding ways to increase C concentrations in soil extracts. A visiting scholar (from Spain) assisted my lab in developing techniques for extracting microbial phospholipids from soils so that these can be analyzed for 13C, and thus provide information on which microbial communities are assimilating the 13C-substrate. We also refined techniques for extracting microbial DNA so that it can be sent to Laurence-Livermore Laboratory in CA and analyzed for 13C and 15N using a state-of-the-art procedure called Chip-SIP. This technique will allow measurement of 13C and 15N in specific microbial genes, and will provide another method of positively identifying which bacteria are active in assimilating the 13C-labelled substrates. Samples from the completed experiments are being processes for 13C-PLFA and Chip-SIP analyses.

    Publications


      Progress 02/15/16 to 02/14/17

      Outputs
      Target Audience:Soil scientists, Ecosystem modelers, Biogeochemists Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?One graduate student and two undergraduate lab assistants have been trained in lab safety and analytical procedures. How have the results been disseminated to communities of interest?Results of the preliminary methodological study were presented at the USDA-NIFA Project Directors meeting in San Francisco in December. What do you plan to do during the next reporting period to accomplish the goals?This year we will continue to recruit a post-doc researcher. We will begin the intensive lab experiments examining the effects of soil moisture and substrate supply on microbial respiration, assimilation, and growth efficiency. During early summer we will begin our novel measurements of growth efficiency in field sites.

      Impacts
      What was accomplished under these goals? This first year was spent recruiting people to work on the grant, purchasing equipment, getting new equipment up and running, and performing some preliminary experiments designed to test and fine-tune the isotope methodologies to be used in the study. We successfully recruited a PhD student, who started her program this fall. We failed to recruit a post-doc, after interviewing and making offers to two individuals. The search will continue this next year following re-advertising the position. We obtained matching funds from the University to upgrade a major piece of equipment (Picarro CO2 analyzer) to one that can measure concentrations and 13C in both CO2 and CH4. This new system (Picarro 2201-i) will provide additional utility to researchers across the university. We have gotten the system up and running and are currently developing calibration procedures. We initiated an experiment to test the ability of gaseous 13C-acetic acid and 15NH3 to provide substrate C and N to microbes in low pH and dry soils. Preliminary results indicate the the method works very well, and that we can proceed with our lab and field experiments examining the effect of soil moisture and C and N supply on soil microbial growth efficiencies.

      Publications