Progress 07/01/16 to 06/30/20
Outputs
Target Audience:The scientific community at large. Results from this investigation are discussed within a larger framework in the "Soil Chemistry" graduate course taught by the PI within the course section on redox chemistry (e.g., coupled redox reactions), thus delivering science-based knowledge in a formal educational setting. The work has also attracted the attention of the earth system science modeling community in the U.S. and Germany, as modelers recognized the value of testing their respective models' representations of carbon-nitrogen dynamics against a rare long-term field study of the fate and redistribution of a 15N tracer (Cheng et al. and Thum et al., below). Changes/Problems:The last set of analyses of the 15N composition of light- and heavy-fraction soil material was submitted for isotopic analysis but was delayed by the COVID-19 pandemic and is still pending. Similarly, analyses from our EMSL collaborators are delayed due to COVID-19. What opportunities for training and professional development has the project provided?This project provided training of a female master student and participation of two undergraduate students in organized research. In addition, this project fostered collaboration with four EMSL scientists, one of which is a young female postdoctoral researcher. The project also provided partial support for two field/lab technicians who have since enrolled in graduate programs (1 MS - Oceanography, North Carolina State and 1 Ph.D. - Environmental & Forest Science, University of Washington), as well as nine undergraduate field/lab assistants, including four women (two underrepresented minority) and five men (4 URM). Among the undergraduate assistants, one completed an undergraduate research project related to this award and two completed undergraduate honors theses; one is now in a Ph.D. program (Plant & Soil Science - U Massachusetts Amherst). How have the results been disseminated to communities of interest?New knowledge is translated into peer review publications and presented at scientific meetings. Results on the long-term fate of tracer 15N have been presented at national (annual meetings of the American Geophysical Union and the Soil Science Society of America - including for an invited symposium) and international conferences (European Geophysical Union, BIOGEOMON Conferences on Ecosystem Behavior). Results of laboratory mesocosm studies were presented at a scientific symposium and within a Cornell University seminar series, and results of the field-scale tracer were presented at both the conferences noted previously as well as in multiple invited seminars at national and international research institutions (see "presentations"). What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Objective 1. Lab-based 15N-tracer studies. (I) Fate of nitrate in organic and mineral horizons of a forest soil under oxic and suboxic conditions. We followed the fate of 15NO3- into soil (organic Oa and iron-rich B) and solution pools and monitored redox-sensitive species in solution. More tracer was recovered in the Oa than in the organic-poor B horizon. For the B horizon, some 15NO3- remained in solution under oxic conditions while the main fate of 15NO3- went unrecovered, due to gaseous losses, under suboxic conditions. Gaseous losses were substantial in the Oa horizon as well. Our results indicate that organic matter drives retention of nitrate under both oxic and suboxic conditions, while lack of OM in iron-rich mineral soils leaves nitrate available for leaching or plant uptake in oxic conditions and enables gaseous loss in suboxic conditions. We posit NO2- serves as a critical intermediate that participates in competing reactions with OM and reduced iron. (II) Nitrate transformation and immobilization in particulate organic matter incubations. Organic matter in the form of leaf compost was spiked with 15NO3- and incubated under oxic-anoxic and biotic-abiotic conditions. We found production of NH4+ is controlled by redox whereas NO3- conversion to dissolved organic N and incorporation in solid-phase N are controlled by abiotic processes. 15N-NMR spectroscopy suggests 15NO3- was incorporated into amide and nitro/oxime under anoxic conditions. Our results also indicate reduced iron did not act as an electron source in biotic-oxic incubations; however, Fe(II) provided electrons for NO3- reduction in biotic-anoxic incubations although it was not the sole electron source. (III) Iron species augment or delay nitrite production in anoxic incubations with organic matter. Organic matter and reduced iron can potentially serve as electron source for nitrate reduction, but it is not clear which electron source is preferred when both are available. We investigate the effect Fe(II) and Fe(III) addition to OM might have on nitrate reduction. We found the rate of nitrate reduction to nitrite was not affected by the presence of Fe2+, however the amount of nitrite produced nearly doubled. Incubations with Fe3+ slowed the rate of nitrite production but the amount of nitrite produced was similar. Our results support the role of Fe(II) as an electron source for nitrate reduction in anoxic incubations; yet, Fe(II) was not the sole electron source. Objective 2. Spectroscopic analyses of N chemical forms. Environmental Molecular Science Laboratory (EMSL) collaboration. We submitted two proposals to the Environmental Molecular Science Laboratory (EMSL), a National Lab funded by the Department of Energy. The proposals were funded, with a total amount of $ 112,957 (in-kind) available to us in the form of instrument time and personnel expertise. In particular, we are able to utilize EMSL's advanced Nuclear Magnetic Resonance (NMR), Electron Paramagnetic Resonance (EPR), Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and liquid chromatography in tandem with FTICR-MS (LC-UV/FTICR-MS) capabilities, and work in collaboration with scientist at EMSL. Coupling of these analysis techniques reveals, at the molecular-scale, how soils incorporate tracer 15NO3- and aid in unraveling the molecular structures of organic N species in soils. We analyze time-resolved soil and solution samples from lab mesocosm studies. We also study the molecular structures of soil organic matter (with focus on organic N) as a function of soil depth in temperate forest ecosystems. Soils collected from the long-term field study, and their heavy fraction and light fraction separates are also analyzed using NMR, EPR and FTICR-MS approaches (Objective 3 below). Samples are currently at EMSL, with analyses of laboratory mesocosms and forest soils with depth almost complete (Obj. 1 and 2), and analyses of long-term field samples (Obj. 3) ongoing. (IV) Character of organic matter in soils of temperate forest ecosystems: Do plant catabolites travel deep? Current theory accepts that organic matter in soils, particularly in deep soil layers, consists of the remains of dead microorganisms (e.g., proteins from necromass). Our studies using N and C XANES spectroscopy and biomolecule extractions however suggest heterocyclic-N containing compounds accumulate at soil depths. We posit the transport and reactivity of plant catabolites deposited at the soil surface comprise a large portion of SOM in deep soils of temperate forest ecosystems. Using 15N-NMR we learned that indeed a peak assigned to heterocyclic-N emerges with soil depth while a peak assigned to amide functionalities decreases. Quantitative CP-TOSS 13C spectra also show a relative increase in aromatic and pyrrole-C with depth over carbohydrate-C. FTICR-MS analyses of water extracts indicate a clear increase in N-containing molecules with depth, with many CHON formulas in the low carbon soil layers. (V) Incorporation of 15N-NO3- into organic and mineral soils: NMR, EPR and FTICR-MS reveal organic N molecular structures. We analyze soil and solution samples from the lab-based 15N-tracer study ((I) above) using EMSL instrument capabilities. EPR analyses so far have shown the Oa horizon yield strong 1H, 13C and 15N signals in HYSCORE (2D EPR) experiments while 1D EPR spectra show signals from Fe, Mn and organic radicals in both Oa and B horizons. The B horizon shows more diversity of Fe species, whereas the free radical signal is stronger in the Oa horizon. FTICRMS analyses show considerably higher amounts of organic molecules in water extracts of Oa, as expected. N-containing formulae (CHON) account for about 2% of all formula while CHO containing formulae account for 85%. Objective 3. Field observations of the decadal-scale fate of a 15N tracer. (VI) Persistent retention of a 15N tracer over a decade in a mixed deciduous forest, with redistribution from shorter- to longer-lived pools. Results show a surprising persistence of the added 15N: ten years after addition, 69% of the added 15NO3- tracer was still present within the ecosystem, with essentially no loss between one and ten years. However the tracer did redistribute within the ecosystem: tracer was steadily lost from surface litter, with those losses balanced by gains in the surface mineral soil (0-20 cm), but not below that depth. This increase in tracer recovery in 0-10 cm mineral soils appears due to an increase of 15N in the heavy fraction mineral material rather than transport of 15N from surface litter into the light fraction. Total recovery of tracer in litter and soil (61.3%) showed a negligible decrease from year 5, an amount exactly balanced by an equivalent increase in plant tissues. In year 10, tracer accumulated into long-lived plant tissues, in old and new wood (2.2%) and coarse roots (2.2%) particularly between 0-20 cm, and decreased in more active plant pools such as foliage (1.2%), bark (0.9%) and fine roots (1.5%) especially at 0-10 cm depth. Tracer recovery in all roots at year 10 amounted to 3.7% of the added tracer, while aboveground plant pools contained 4.4%. Species differences in tracer recovery sharpened over time, such that by year 10, all six tree species with ECM (ectomycorrhizae) associations had notably greater 15N enrichment in foliage than all four tree species with AM (arbuscular mycorrhizal) associations. Enrichment diminished over time in both groups, but more steeply in ECM foliage. Together, these results show near-constant, tight retention of added 15N a full decade after its addition, with tracer moving from litter to deeper soils and from shorter- to longer-lived plant pools, both of which should enhance the long-term stability of retained N within the ecosystem. Four of the aforementioned manuscripts are "In preparation". We will acknowledge funding from this award when published.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2019
Citation:
Kizewski, F.R.; Kaye, J.; Mart�nez, C.E. 2019. Nitrate transformation and immobilization in particulate organic matter incubations: Influence of redox, iron, and (a)biotic conditions. PLoS ONE 14 (7): e0218752. https://doi.org/10.1371/journal.pone.0218752.
- Type:
Journal Articles
Status:
Under Review
Year Published:
2020
Citation:
Mollhagen, A.; Goodale, C.L.; Mart�nez, C.E. 2020. Contrasting fates of nitrate between organic and mineral horizons of an acidic forest soil under oxic and suboxic conditions. Soil Biology and Biochemistry, under review.
- Type:
Journal Articles
Status:
Other
Year Published:
2020
Citation:
Kizewski, F.R.; Mart�nez, C.E. Iron redox species augment (ferrous iron) or delay (ferric iron) nitrite production in anoxic incubations with particulate organic matter. In preparation.
- Type:
Journal Articles
Status:
Other
Year Published:
2020
Citation:
Mart�nez, C.E.; Walter, E.D.; Lipton, A.S.; Didonato, N.; Washton, N.M.; Schmidt, M.P.; Fine, A.K. Character of organic matter in soils of temperate forest ecosystems: Do plant catabolites travel deep? In preparation.
- Type:
Journal Articles
Status:
Other
Year Published:
2020
Citation:
Mart�nez, C.E.; Didonato, N.; Lipton, A.S.; Walter, E.D.; Washton, N.M.; Goodale, C.L. Incorporation of 15N-NO3- into organic and mineral soils: NMR, EPR and FTICR-MS reveal differences in organic molecular structures formed under oxic and suboxic conditions. In preparation.
- Type:
Journal Articles
Status:
Other
Year Published:
2020
Citation:
Goodale, C.L.; Mart�nez, C.E. Persistent retention of a 15N tracer over a decade in a mixed deciduous forest, with redistribution from shorter- to longer-lived pools. In preparation.
- Type:
Journal Articles
Status:
Other
Year Published:
2020
Citation:
Goodale, C.L.; Mart�nez, C.E. Changes over a decade of the fate and form of a 15N-NO3 tracer in light- and heavy soil fractions in a mixed deciduous forest. In preparation.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
DiDonato, N.; Clendinen, C.; Rivas-Ubach, A.; Mart�nez, C.E.; Tolic, N.; Sokol, N.; Adhikari, D.; Pett-Ridge, J.; Pasa-Tolic, L. 2020. Assessing soil organic matter features as detected with direct infusion high resolution mass spectrometry and LC-MS-MS feature based molecular networking. 2nd Annual Metabolomics Association of North America (MANA) Conference, Sept 14-16, Virtual.
- Type:
Conference Papers and Presentations
Status:
Accepted
Year Published:
2021
Citation:
Thum, T., C. Goodale, S. Caldararu, J. Engel, L. Yu, and S. Zaehle. 2020. Using 15N tracer experiments with at land surface model to assess nitrogen cycling modelling. BIOGEOMON 10th International symposium on ecosystem behavior, Tartu Estonia; abstract submitted; conference postponed from July 2020 to June 2021 due to the COVID-19 pandemic.
- Type:
Theses/Dissertations
Status:
Published
Year Published:
2019
Citation:
Mollhagen, Ariel. Tracing Nitrate Transformations in a Forest Soil. Department Seminar presented at the Soil and Crop Sciences Seminar series, Cornell University, April 26, 2019.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Goodale, C.L., S.J. Cheng, C.E. Mart�nez. Decadal redistribution of a 15N tracer in a mixed deciduous forest. European Geosciences Union annual meeting, Vienna, Austria, April 2019.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Thum, T., S. Caldararu, L. Yu, M. Kern, J. Engel, M. Pallandt, B. Ahrens, C. Goodale, and S. Zaehle. Using 15N natural abundance and tracer studies to constrain simulated nitrogen dynamics in forest ecosystems under changing atmospheric CO2 concentrations. European Geosciences Union annual meeting, Vienna, Austria, April 2019.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Goodale, C.L. and C.E. Mart�nez. Decadal redistribution of a 15N tracer in a mixed deciduous forest. SSSA International Soils Meeting, San Diego, CA, January 6-9, 2019.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Goodale, CL, et al. Cornell University, Department of Natural Resources, Nitrogen Fate and Effects on Carbon Storage November 25, 2019
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Goodale, CL, et al. Virginia Tech, Nitrogen Fate and Effects on Carbon Storage, Blacksburg, VA, March 8, 2019
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2018
Citation:
Cheng, S.J., P.G.M. Hess, W.R. Wieder, R.Q. Thomas, K.J. Nadelhoffer, J. Vira, D.L. Lombardozzi, P. Gundersen, I.J. Fernandez, P. Schleppi, M.C. Cruselle, F. Moldan, and C.L. Goodale. Evaluating the impacts of short and long-term fates of nitrogen additions on forest carbon pools in Earth system models. American Geophysical Union Fall Meeting, Washington DC, Dec. 2018
- Type:
Journal Articles
Status:
Published
Year Published:
2019
Citation:
Cheng, SJ, PG Hess, WR Wieder, RQ Thomas, KJ Nadelhoffer, J Vira, DL Lombardozzi, P Gundersen, IJ Fernandez, P Schleppi, M-C Gruselle, F Moldan, CL Goodale. 2019. Decadal fates and impacts of nitrogen additions on temperate forest carbon sinks: a data-model comparison. Biogeosciences https://doi.org/10.5194/bg-16-2771-2019.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2018
Citation:
Mollhagen, A. Isotopic Investigation of Redox Effects on Nitrate Partitioning in a Forest Soil. Poster session presented at the NADP Scientific Symposium and Fall Meeting, Albany, NY, November 5, 2018.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2018
Citation:
Goodale, CL, et al. Max Planck Institute for Biogeochemistry, Nitrogen Fate and Effects on Carbon Storage, Jena, Germany, Nov. 1, 2018
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2018
Citation:
Goodale, CL, et al. Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research - Atmospheric Environmental Research (KIT/IMK-IFU), Nitrogen Fate and Effects on Carbon Storage, Garmisch-Partenkirchen, Germany, June 14, 2018
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2018
Citation:
Goodale, CL, et al. Dartmouth College, Department of Biology, Nitrogen Deposition, Nitrogen Retention, and Forest Carbon Storage Jan. 26, 2018
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2017
Citation:
Goodale, C.L .and C.E. Mart�nez. Multiyear fate of a 15N tracer in a mixed deciduous forest. Symposium: New Insights on Biogeochemical Processes in Forest Ecosystems as Revealed by Isotopic and Biomarker Approaches. Soil Science Society of America Annual Meeting, Tampa FL Oct. 22-25, 2017. Invited oral presentation.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2017
Citation:
Goodale, C.L. and C.E. Mart�nez. Multiyear fate of a 15N tracer in a mixed deciduous forest: retention, redistribution, and differences by mycorrhizal association. BIOGEOMON 2017. International Symposium on Ecosystem Behavior, Litomysl, Czech Republic, August 2017. Contributed poster presentation.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2017
Citation:
Goodale, C.L. Nitrogen fate and impacts in temperate forests: roles of mycorrhizae and pH. European Geophysical Union Annual Meeting. Vienna, Austria, April 24-28, 2017. Invited oral presentation
|
Progress 07/01/17 to 06/30/18
Outputs
Target Audience:The scientific community at large. Results from this investigation are discussed within a larger framework (e.g., coupled redox reactions) in the "Soil Chemistry" graduate course taught by the PI within the course section on redox chemistry, thus delivering science-based knowledge in a formal educational setting. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This project has provided training of a master student and participation of two undergraduate student in organized research. How have the results been disseminated to communities of interest?New knowledge is translated into peer review publications (one "under review", a second "in preparation") and presented at scientific meetings. Results on the long-term fate of tracer 15N were presented at an international conferences and results of laboratory mesocosm studies were presented at a scientific symposium and within a Cornell University seminar series. What do you plan to do during the next reporting period to accomplish the goals?Laboratory 15N-tracer mesocosm incubations and analyses with soil horizons (Oa, A, E, B) under oxic conditions are completed whereas those under suboxic conditions are under way. Processing (sieving, sorting, grinding) for the > 500 field samples collected is almost complete and isotopic and chemical analyses of soil and plant samples are ongoing. The plan is to have all research completed and published by the end of the no-cost extension.
Impacts
What was accomplished under these goals?
Laboratory mesocosm studies under oxic conditions with Oa, A, E and B horizons from Arnot soils are completed and the data analyzed. For experiments under oxic conditions, oxygen gas (O2) was bubbled continuously into experimental jars to maintain a redox potential of 550 mV throughout the duration of the experiments. This was attained using a home-built data logging meter connected to a real-time plotting and logging script assembled and operated with open source hardware and software. Nitrite concentrations in solution were below the limit of detection for all horizons throughout the 30 day duration of experiments. Nitrate solution concentrations dropped to below detection in the Oa-horizon after 5-10 days of incubation, decreased slightly with time in the A-horizon, but remained unchanged in the E and B horizons. Ammonium and total nitrogen concentrations followed the trend: Oa > A > E > B, with a similar pattern of increased concentrations in the Oa and A horizons; however ammonium and total nitrogen concentrations increased in the E and B horizons only after 20 days of incubation. Dissolved organic carbon (DOC) concentrations increased significantly with time in the Oa horizon, modestly in the A horizon, and remained unchanged (above the detection limit) in the E and B horizons. We also determined solution concentrations for redox-sensitive metal species, namely iron (Fe) and manganese (Mn), that might be involved in coupled N-metal biogeochemical cycles. Total dissolved manganese concentrations (presumably Mn2+) remained constant in the Oa, A and E horizons with time, and were highest in the Oa and lowest in the E horizon. In contrast, Mn concentrations increased dramatically in the B horizon reaching a plateau after 20 days. Considerable variability was observed in the behavior of ferrous (Fe2+) and ferric (Fe3+) iron among horizons and as a function of time. Higher concentrations of Fe2+ were observed with time in the Oa and A horizons, higher Fe3+ was present in the E horizon, while equal concentrations of Fe2+ and Fe3+, which decreased with time, were determined in the B horizon. The presence of reduced Mn (Mn2+) and Fe (Fe2+) species is however expected based on theoretical redox potentials for the manganese-oxide(MnO2)-Mn2+ and iron-oxide(Fe(OH)2)-Fe2+ half-cell reactions in water at pH of 4. In addition, the presence of dissolved organic carbon (DOC) might induce further reduction of these metals in solution. Isotopic analyses of soil and solution pools indicate 60 to 80% total 15N recoveries in soil plus solution pools. Twenty to 60% of the 15N-NO3 label is recovered in soil. 15N soil-solution partitioning is however affected by horizon, with % recovery in the soil following the order: Oa (60%) > A (50%) > B (22%) > E (20%) at experiment end. The E horizon is the only horizon not to reach equilibrium by approx. 15 days. The rate and quantity of 15N-NO3 incorporation into soil roughly scales with organic matter content, the B horizon being an exception. Notably, living microbial biomass accounts for very little of the recovered label at any given time. 15N-NO3 label recovery in solution was: E (65%) > B (30%) > A (12%) > Oa (10%) at experiment end. Comparison of soil and solution 15N label recovery indicates the transference of 15N-NO3 from solution to solid was also accompanied by large losses from the system (15-50%), with the largest 15N label loss from the B horizon. The B horizon had very low dissolved Fe (Fe2+ and Fe3+) concentrations (at the detection limit) at experiment end, but the highest dissolved Mn concentration. We will continue to decipher the chemistry behind the trends observed. An important development in the last year is that we were awarded instrument time at the Environmental Molecular Science Laboratory (EMSL) within Pacific Northwest National Laboratory (PNNL). Utilizing EMSL's advanced Nuclear Magnetic Resonance (NMR), Electron Paramagnetic Resonance (EPR), and 21T Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) capabilities and scientific expertise, we will learn, at the molecular-scale, how soils incorporate tracer 15N-NO3- into their structure to form soil organic nitrogen (SON) as well as dissolved organic nitrogen (DON) species. Coupling of advanced NMR, EPR and high-resolution FTICR-MS analyses will aid in unraveling the molecular structures of organic N species in soils (SON and DON). We will analyze time-resolved (from time zero to approx. 30 days) soil samples from laboratory mesocosm studies for NMR, EPR and FTICR-MS analyses of soil extracts as well as corresponding aqueous phase (soil solution) samples for FTICR-MS analyses. Soils collected from the long-term field study (up to 10 years), and their heavy fraction (HF) and light fraction (LF) separates will also be analyzed using NMR, EPR and FTICR-MS approaches. Samples are currently at EMSL and analyses are ongoing.
Publications
- Type:
Journal Articles
Status:
Under Review
Year Published:
2019
Citation:
Kizewski, F.R.; Kaye, J.; Mart�nez, C.E. 2019. Nitrate transformation and immobilization in organic matter incubations: influence of redox, iron, and (a)biotic conditions. Under review.
- Type:
Conference Papers and Presentations
Status:
Other
Year Published:
2019
Citation:
Mollhagen, Ariel. Tracing Nitrate Transformations in a Forest Soil. Department Seminar presented at the Soil and Crop Sciences Seminar, Cornell University, April 26, 2019.
- Type:
Conference Papers and Presentations
Status:
Accepted
Year Published:
2019
Citation:
Goodale, CL and CE Mart�nez. Decadal redistribution of a 15N tracer in a mixed deciduous forest. SSSA International Soils Meeting, San Diego, CA, January 6-9, 2019.
- Type:
Conference Papers and Presentations
Status:
Accepted
Year Published:
2018
Citation:
Mollhagen, Ariel. Isotopic Investigation of Redox Effects on Nitrate Partitioning in a Forest Soil. Poster session presented at the NADP Scientific Symposium and Fall Meeting, Albany, NY, November 5, 2018.
|
Progress 07/01/16 to 06/30/17
Outputs
Target Audience:The scientific community at large. Results from this investigation are discussed within a larger framework (e.g., coupled redox reactions) in the "Soil Chemistry" graduate course taught by the PI within the course section on redox chemistry, thus delivering science-based knowledge in a formal educational setting. Changes/Problems:We got notification this project was funded late in the spring of 2016, with a project start date of July 1, 2016. Due to the proximity to the beginning of the school academic year, a graduate student was recruited to work on this project starting in the Fall of 2017. All of the project objectives will be fulfilled; we will however submit paperwork to request a 1-year no-cost extension. What opportunities for training and professional development has the project provided?This project has provided training of a master student and participation of an undergraduate student in organized research. How have the results been disseminated to communities of interest?New knowledge will be translated into peer review publications and presented at scientific meetings. Preliminary results on the long-term fate of tracer 15N have been presented at two international conferences (European Geophysical Union, BIOGEOMON Conference on Ecosystem Behavior) and as part of an invited presentation to a symposium at the Soil Science Society of America Annual Meeting. What do you plan to do during the next reporting period to accomplish the goals?We will work towards completing all of the experiments detailed under objectives 1 to 3. More specifically, lab-based 15N-tracer experiments under biotic-oxic and biotic-suboxic conditions for each soil horizon (Oa, A, E, B) will be completed and experiments under abiotic conditions will be started. Processing (sieving, sorting, grinding) and isotopic analyses will be completed for the > 500 field samples collected during summer 2017.
Impacts
What was accomplished under these goals?
Objective 1, 2. Lab-based 15N-tracer experiments. A soil pit was dug at Arnot Forest and enough soil was collected from each horizon (Oa, A, E, and B) to conduct laboratory mesocosm incubations. Total organic carbon and total nitrogen content follow trends typical of forest soils, namely, 38.4, 19.9, 6.9 and 2.3 % carbon, and 1.5, 0.8, 0.3 and 0.1 % nitrogen for Oa, A, E and B horizons, respectively. We have developed protocols for quantification of aqueous species of interest (e.g., nitrate, nitrite, ammonium, ferrous and ferric iron, manganese). Preliminary mesocosm experiments showed the redox potential of open top stirred soil slurries (1:8 soil:water) for all horizons fall within the suboxic range (Eh = 300-400 mV) at pH values between approximately 4 and 4.5. We also learned that 5-6 days are required for Eh and pH values to stabilize, that is, a pre-incubation period is required before the start of the mesocosm 15N-tracer studies. In addition, instead of bubbling gases to decrease the redox status of the soils to a sub-oxic condition, as we had expected, our preliminary studies indicate we will have to bubble air to increase the redox status to an oxic condition. Objective 3. Field observations of the decadal-scale fate of a 15N tracer. During summer 2017, a large set of field samples were collected to enable complete assessment of the redistribution and fate of a 15N-NO3 tracer applied 10 years earlier to a 0.25 hectare mixed deciduous plot. Wood and bark were collected from 33 trees representing 10 species (4 with arbuscular mycorrhizal (AM) associations and 6 with ectomycorrhizae (ECM)), in triplicate, using an increment borer to obtain wood samples in tree rings from both pre- and post-tracer addition. Foliage was collected by shotgun from these same 33 trees. Surface litter (Oi layer) material was collected from 40 locations distributed across 20 subplots (2 per subplot). Twenty quantitative 9.5 cm diameter soil cores (1 per subplot) were collected to 50 cm depth in 10 cm increments using a gas-powered diamond-bit corer. These soil samples provide both soil and root (fine and coarse) material that are separated during processing. Litterfall was collected with 20 litter baskets (1 per subplot) during autumn 2017, with a last litter collection pending in early spring 2018. Processing of these samples for stable isotopic analysis is under way. Additional grab samples of foliar litter from 9 tree species were collected during October 2016 (year 9). These samples provided for a preliminary assessment of tracer persistence. They showed only small decreases in 15N enrichment in some tree species between 1 and 9 years after tracer addition. Analyses showed persistently greater enrichment in ECM than AM tree species, with parallel decreases by ~4‰ in both AM and ECM tree species. The persistent enrichment after 9 years implies substantial recycling of tracer 15N by both AM and ECM species, despite annual losses of N in plant litter.
Publications
- Type:
Conference Papers and Presentations
Status:
Other
Year Published:
2017
Citation:
Goodale, CL and CE Mart�nez. Multiyear fate of a 15N tracer in a mixed deciduous forest. Symposium: New Insights on Biogeochemical Processes in Forest Ecosystems as Revealed by Isotopic and Biomarker Approaches. Soil Science Society of America Annual Meeting, Tampa FL Oct. 22-25, 2017. Invited oral presentation.
- Type:
Conference Papers and Presentations
Status:
Other
Year Published:
2017
Citation:
Goodale, CL and CE Mart�nez. Multiyear fate of a 15N tracer in a mixed deciduous forest: retention, redistribution, and differences by mycorrhizal association. BIOGEOMON 2017. International Symposium on Ecosystem Behavior, Litomysl, Czech Republic, August 2017. Contributed poster presentation.
- Type:
Conference Papers and Presentations
Status:
Other
Year Published:
2017
Citation:
Goodale, CL. Nitrogen fate and impacts in temperate forests: roles of mycorrhizae and pH. European Geophysical Union Annual Meeting. Vienna, Austria, April 24-28, 2017. Invited oral presentation.
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