NUTRIENT V. ACIDIFICATION? EFFECTS OF NITROGEN AVAILABILITY ON DECOMPOSITION AND SOIL CARBON STORAGE

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: ACTIVE
• Funding Source: AFRI COMPETITIVE GRANT
• Reporting Frequency: Annual
• Accession No.: 1027699
• Grant No.: 2022-67019-36108
• Cumulative Award Amt.: $749,999.00
• Proposal No.: 2021-09219
• Project Start Date: Jan 1, 2022
• Project End Date: Dec 31, 2025
• Grant Year: 2022
• Program Code: [A1401]- Foundational Program: Soil Health

Recipient Organization
CORNELL UNIVERSITY
(N/A)
ITHACA,NY 14853

Performing Department
EEB

Non Technical Summary
Soils retain large pools of carbon and cycle nutrients that sustain forest productivity; together these processes can slow climate change. Understanding of the controls on soil carbon storage increasingly recognizes the importance of microbial turnover, plant belowground allocation, and stabilization in mineral soils, as well as the interaction of these processes with nutrient availability. Yet, both experiments and earth system models regularly neglect the dual roles of nitrogen as not only a nutrient but also an acidifier, despite the biogeochemical importance of pH. The overall goal of this project is to test hypothesized mechanisms of how nitrogen availability and pH independently and interactively alter soil carbon storage. These processes include: 1) stimulation or suppression of microbial growth, consumption of particulate organic matter, and formation of mineral-associated organic matter; (2) changes to aboveground plant and litter production; (3) alterations of plant belowground carbon allocation; and (4) changes in sorption of dissolved organic matter onto mineral surfaces. We propose to test these mechanisms with a suite of new measurements of soil particulate and mineral-associated organic matter pools as well as the fate of dual-labeled (13C, 15N) litter; plant productivity and belowground allocation to roots, mycorrhizae, and root exudates as well as exudate composition; and dissolved organic matter composition and sorption, all at a large-scale long-term nitrogen by pH manipulation experiment in mixed deciduous forests. Together, the proposed research supports the goals of the USDA-AFRI Soil Health Program Area to advance scientific understanding of soil biogeochemical interactions and enable improvements to both models and long-term forest management to store carbon and sustain production of timber and biofuels.

Animal Health Component

20%

Research Effort Categories

Basic

80%

Applied

20%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
102	0110	1070	100%

Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships;

Subject Of Investigation
0110 - Soil;

Field Of Science
1070 - Ecology;

Keywords

acidification

belowground allocation

decomposition

nitrogen availability

soil carbon storage

Goals / Objectives
The overall goal of the proposed project is to test and quantify multiple mechanisms of nutrient-N and acidification effects on the amount, form, and stability of soil C, at scales spanning soil molecular chemistry, plant C allocation to roots, mycorrhizae, and root exudates, and whole-ecosystem C-N dynamics. The four objectives below will test four hypothesized sets of mechanisms (H1-4) of how nutrient-N and acidification can independently and interactively alter soil C storage and stabilizationObjective 1: Determine whether (H1) additions of N as a nutrient increase microbial biomass and turnover, losses of particulate organic matter and C stabilization in mineral-associated organic matter, and whether soil acidification has the opposite suite of effects.Objective 2: Determine whether (H2) nutrient-N addition increases the inputs of aboveground litter to soil, and whether nutrient imbalances induced by acidification limit or reduce aboveground plant growth and litter inputs.Objective 3: Determine whether (H3) plant allocation of C belowground to roots, mycorrhizae, and exudates vary inversely with soil N availability, and thus decrease with N addition and change little or increase with acidification.Objective 4 Determine whether (H4) dissolved organic matter (DOM) composition and DOM sorption to soil minerals (i.e., formation of MAOM) are altered by N and acidification.

Project Methods
A long-term N x pH manipulation experiment was initiated in 2011 in six forest stands near Ithaca, NY, at a pair of stands at each of three sites: a "primary" forest stand with little or no harvest and no history of cultivation, and a "secondary" forest abandoned from agriculture ~100 years earlier. At each stand, four large plots (60 x 60 m) were established for baseline measurements of plant and soil C stocks and aboveground NPP. Treatments consist of a control, two forms of N both at 50 kg N ha-1 yr-1 selected to either raise (NaNO3) or lower ((NH4)2SO4) soil pH, and elemental sulfur to acidify without N. Amendments are applied in pelletized form using hand-held fertilizer spreaders across the full 60 x 60 m area.At each plot, plant and soil C measurements occur within an interior plot area (40 x 40 m), with a 10 m buffer on all sides. Tree biomass and wood production are assessed by periodic inventory. Tree species composition varies across the six stands, such that 24 to 92% of tree biomass is composed of species that typically associate with arbuscular (AM) mycorrhizae while the rest is composed of typically ectomycorrhizal (ECM) tree species. Soils at all three sites are classified as moderately to very strongly acid channery silt loam Inceptisols developed in glacial till deposited on Devonian shale bedrock). Soil C, N, and S stocks and pH were determined to 50 cm depth after quantitative sampling in 10 cm increments using a rotary corer.We will conduct a suite of new field measurements to address each of our four hypothesized mechanisms by which nutrient-N and acidification could alter soil C storage by affecting (H1) microbial processing and formation of particulate- and mineral associated organic matter; (2) aboveground NPP; (3) belowground C allocation to roots, mycorrhizae, and root exudates, as well as exudate composition; and (4) composition and sorption of DOM.To address H1, we will re-measure soil C stocks in 2022 after more than a decade of N x pH treatments, and we will conduct new measurements of microbial biomass, POM, and MAOM. In addition, a new double-labeled (13C and 15N) litter experiment will enable refined partitioning of how N and pH alter the fate of new litter into various organic matter pools.To address H2, we will re-measure aboveground net primary production to assess whether nutrient-N stimulation of aboveground tree growth has persisted in NaNO3 treatments, and whether negative consequence from acidification have emerged over time in S and (NH4)2SO4 treatments. This study will uniquely allow separation of the nutrient and acidification components of these growth responses, and how it affects various components plant C allocation. To assess whether any of the treatments have induced potential growth limitations by base cations or phosphorus, we will measure litter base cation chemistry in both newly collected and archived pre-treatment leaf litter and soil samples. Together, these measurements of wood production and litterfall provide estimates of plant production and allocation aboveground, how it responds to nutrient-N addition and acidification, and how it compares with response belowground C allocation.H3 will be addressed by measuring plant C allocation responses to N x pH treatment and corresponding effects on N availability. Measurements of potential N mineralization rates will provide an index of N availability across sites, and show if it has been altered by long-term N addition and acidification. Belowground C measurements will include responses of annual soil respiration (Rsoil) and total belowground carbon allocation (TBCA) to provide overall constraints on total plant allocation belowground. Additional measurements of root, mycorrhizal, and exudate production will allow partitioning of TBCA responses as well as independent measures of the sensitivity of each components to N and pH treatments.H4 will be addressed by comparing the amount and chemical composition of initial dissolved organic matter samples from acidification and nutrient-N treatments, through use of 2-dimensional nuclear magnetic resonance imaging (2S NMR). Using 2D NMR analyses we will be able to determine which organic functionalities are adsorbed and which are not, that is, how the signal 2D "landscape" changes upon sorption. In addition, DOM batch sorption experiments will be conducted on surface soils collected during soil resampling (H1). These analyses will determine how DOC sorption responds to N- and acidification treatments. Surface mineral soils are characterized by XRD, Al and Fe selective extractions and CEC to relate sorption behavior to soil properties.

Progress 01/01/24 to 12/31/24

Outputs
Target Audience:The target audience is primarily soil- and forest scientists involved forest carbon management, soil health, and ecosystem ecology. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project has provided research opportunities for one postdoc (Ben Hafner, root exudates), three graduate students (Dave Frey, researching soil respiration and root production; Stephanie Freund, studying plant nitrogen uptake, and Alyssa de Villiers studying DOM characterizations using a range of advanced techniques, including X-ray diffraction (XRD) and transmission electron microscopy (TEM)), as well as six undergraduates on the 2024 field & lab crew (Sachi Srivastava, Lena Cenegotitabengoa, Katherine Cabal Volquez, Weidei Sun, Alessandro Topa, and Emma Pereira), and three technicians (Matthew Hecking, Jacob Scharfetter, and Claire Schmucker). It also supported the presentations by three project trainees at major national and international conference: by graduate student Dave Frey at the BIOGEOMON Conference on Ecosystem Behavior in Jan. 2024; by graduate student Alyssa de Villiers at the Soil Science Society of America (SSSA) conference in June 2024; and by postdoc Ben Hafner at the annual meeting of German ecologists in Sept. 2024. How have the results been disseminated to communities of interest?We have shared project results at several major national and international conferences during 2024, including the Biogeomon conference on ecosystem behavior (one talk), the Soil Science Society of America (one poster), and the Ecological Society of Germany, Austria, and Switzerland (one talk). In addition, field measurements from our study were included in a large data synthesis effort of root exudation measurements published during 2024 (Chari et al., 2024, Biogeochemistry). Two other manuscripts were submitted for publication: collaborator Perakowski et al. submitted research on the responses of leaf photosynthesis and water- and nutrient use efficiency in response to N and pH to Tree Physiology in December 2024, and Frey et al. submitted work on N and pH effects on soil respiration to Global Change Biology for which reviews were received in Nov. 2024, and the revised manuscript was accepted for publication on 2/28/25. What do you plan to do during the next reporting period to accomplish the goals?For 2025, we expect to wrap up all outstanding project sample analyses, and submit several corresponding manuscripts. First, we will conduct the 15th year of forest N and S amendments in early spring 2025. For Objective 1, we completed soil fractionation measurements and are awaiting results of corresponding 13C analyses; similarly, we are awaiting 13C analyses for our corn-litter tracer study; at least one manuscript should result. For Objective 2, in 2022 we completed the measurements of aboveground productivity stated in our proposal; results are included in a manuscript we intend to submit I late spring 2025. An additional manuscript on the carbon cost of plant N uptake is anticipated for late 2025, with presentation at the 2025 Ecological Society of American annual meeting. In Aug/Sept 2025, we will conduct an additional round of measurements of wood production. For Objective 3, we have completed our proposal's stated measurements of soil respiration, total belowground C flux, and root production; the soil respiration data have been recently accepted for publication in 2025 by Global Change Biology. Submission of a second manuscript on total belowground C flux is pending for late spring. Rates of root exudation were measured previously, while measurements of the metabolomic of these exudates are in progress. At least two manuscripts are anticipated from the root exudate work by late 2025. Finally, for object 4, we plan to examine the optical properties of collected and frozen root exudates. Sorption and stability (sorption-desorption) of DOM components will be investigated further using in situ Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (in situ ATR-FTIR). These studies will tell us how (mechanisms) and how fast (kinetics) DOM is accumulated and released from mineral surfaces in the presence of root exudates. Expected outputs for this objective during 2025 include two papers, one on treatment effects by depth and one on the batch and in situ spectroscopic sorption-desorption studies, as well as presentation as a conference such as the American Geophysical Union (AGU) 2025.

Impacts
What was accomplished under these goals? During 2024, we completed this award's planned major tasks largely as planned last year. In late spring 2024, the fourteenth year of amendments was applied to our nitrogen- by pH manipulation experiment, replicated in six forest stands (3 primary forest, 3 secondary forest) near Ithaca, NY. Each stand contains four 40 x 40 m plots used to characterize tree growth and soil properties. Treatments are applied to 60 x 60 m areas consisting of the central plots with 10 m treated buffer. Treatments consist of two nitrogen additions at 50 kg N per hectare per year, one selected to raise soil pH (sodium nitrate) and one to acidify (ammonium sulfate). A third treatment uses elemental sulfur to acidify without nitrogen, and the fourth plots serve as controls. For Objective 1, assessing whether N and pH have altered microbial biomass and soil organic matter (SOM) storage into light (POM) and heavy (MAOM) pools, we quantitatively resampled SOM by soil depth (forest floor, 0-3, 3-10, 10-20 cm) in June & July, 2022 in all 24 forest plots. During 2023, we completed soil processing (sieving, grinding, weighting, etc.) and a range of lab measurements on 360 samples (24 plots x 5 locations/plot x 3 depths/location) to quantify soil C, and N, and their isotopic composition. In mid-2024, we received measurements on C and N concentration and 13C composition, and are presently working up data for statistical analysis and publication. We also completed fractionating soil samples for POM and MAOM analyses, and are preparing samples for 13C analysis in early 2025. As a second approach to study how N x pH treatments alter the formation of POM and MAOM, in October, 2022, we initiated a litter decomposition experiment with isotopically distinct leaf litter. For this experiment, we deployed replicated sets of ~0.1 m^2 blocks (five sets of three blocks per plot) that replaced that year's leaf litter with corn leaf litter, selected to serve as an inexpensive and abundant decomposition substrate with a distinctive carbon isotopic composition that can be traced into newly formed POM and MAOM in blocks to be destructively sampled 1, 2, and 5 years after deployment. During October, 2023, we conducted the first set of samplings, carefully extracting 360 samples and returning them to the lab for drying, weighing, and preparation for isotope analysis. These measurements were processed during 2024, and submitted for 13C analysis in Dec. 2024. For Objective 2, assessing whether N and pH have altered aboveground plant growth, in August and September 2022 we completed a full re-inventory of the diameter of all trees > 9.5 cm diameter. Aboveground litterfall was also collected from all plots during autumn 2022, with an additional overwinter litterfall collection planned for early spring 2023. An additional suite of measurements of the N content of these tissues (wood, bark, litterfall) and in newly produced roots (below) will allow estimates ecosystem-scale measurements of plant nitrogen uptake, to be used to assess the fate and efficiency of the applied N, as well as the belowground C expended by plants to take up this N. In 2023, we added further information to the plant-level N budget by collecting canopy foliage from the 3-4 dominant species on each plot for analysis of N content. We also conducted a suite of measurements of root-level N uptake for the most dominant species on the primary (sugar maple) and secondary (red maple) forest plots. In 2024, the extensive measurements of aboveground plant growth from 1000s of trees were used to compute plant C gain, and a manuscript has been drafted and for submission in spring 2025. These measurements were combined with measurements of tissues N content to estimate plant N uptake, which we expect to present at the Aug. 2025 Ecological Society of America annual meeting. For Objective 3, assessing N x pH effects on plant C allocation belowground, annual soil respiration measurements were compiled across all 24 plots in 2021. Root biomass measurements were conducted over collected as part of the soil sampling efforts described in Objective 1, and measurements of root production into root ingrowth cores have been collected, and were picked, dried, and weighed during 2022-2023. In 2022 we also completed an additional study of soil heterotrophic respiration using all of the soil samples collected in Objective 1, that complement the field measurements of soil respiration, and allow a novel partitioning of soil respiration into heterotrophic and root-related respiration components. A paper describing this work was submitted for publication in October 2024, and was accepted on Feb. 28, 2025. Last, in situ root exudate collections were successfully collected from six stands in 2023, and measurements of their metabololomics are under way. For Objective 4, assessing N x pH effects on the composition and sorption of dissolved organic matter (DOM), sample processing began during fall 2022 to extract DOM from soil samples collected as part of Objective 1. Composition of the water-extractable DOM fraction < 0.2 µm were evaluated using pH, nitrate, ammonium, aluminum, phosphate, total organic carbon, total nitrogen, and a suite of optical properties (SUVA254 for aromaticity, slope ratio for molecular weight, excitation-emission matrices (EEMs) for humification index, biological index, and fluorescence index). During 2024, we completed cation analysis (calcium, magnesium, potassium) and characterization by Fourier-transform infrared spectroscopy (FTIR) on the water-extracted soil samples as well as finish the remaining EEMs. We also completed a batch sorption study looking at the interaction between dissolved organic matter (DOM) extracted from the 0-3cm A horizon and three soil minerals commonly found in the northeastern United States, namely goethite, gibbsite and kaolinite. In total, we have made enormous progress toward fully completing all project objectives, and we anticipate submitting and completing multiple publication over the next year.

Publications

• Type: Theses/Dissertations Status: Published Year Published: 2024 Citation: Frey, DW. Effects of soil nutrient availability, acidification, and deacidification on aboveground and belowground carbon cycling in mixed temperate forests. Doctoral dissertation, Cornell University, Dec. 2024.
• Type: Other Journal Articles Status: Accepted Year Published: 2025 Citation: Frey, DW, ET Kebede, TJ Fahey, CL Goodale. In revision. Increased soil nitrogen availability suppresses annual soil respiration in mixed temperate forests regardless of acidification. Global Change Biology
• Type: Other Journal Articles Status: Under Review Year Published: 2025 Citation: Perakowski, E, DW Frey, CL Goodale, N Smith. In review. Increasing nitrogen availability increases water use efficiency and decreases nitrogen use efficiency in Acer saccharum. Tree Physiology.
• Type: Other Journal Articles Status: Published Year Published: 2024 Citation: Chari, NR, SJ Tumber-D�vila, RP Phillips, TL Bauerle, M Brunn, BD Hafner, T Klein, S Obersteiner, MK Reay, S Ullah, BN Taylor, B. N. 2024. Estimating the global root exudate carbon flux. Biogeochemistry,167, 895908
• Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: Frey, DW, ET Kebede, CL Goodale. Disentangling nitrogens role as a limiting nutrient and acidifier: how does nitrogen availability affect soil respiration? BIOGEOMON conference, San Juan Puerto Rico, Jan. 2024
• Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: de Villiers, CE Martinez. Do Forest Ecosystem-Level Changes Alter Dissolved Organic Matter (DOM) Composition and Subsequent Carbon Retention? Soil Science Society of America 2024 Summer Conference, San Juan Puerto Rico, June 2024
• Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: Hafner BD, Brunn M, Goodale CL and Bauerle TL. Tree carbon allocation to root exudates in temperate biomes under varying environmental conditions. Gf�, Annual Meeting of the Ecological Society of Germany, Austria, and Switzerland. Freising, Germany, Sept. 2024
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2024 Citation: Goodale, C, T Bauerle, A de Villiers, D Frey, S Freund, B Hafner, M Hecking, E Kebede, W King, CE Martinez. 2024. Nutrient v. Acidification: Effects of Nitrogen Availability on Decomposition and Soil Carbon Storage. USDA Soil Health Program PI Meeting, Poster and Flash Talk. April 9-11, 2024

Progress 01/01/23 to 12/31/23

Outputs
Target Audience:The target audience is primarily soil- and forest scientists involved forest carbon management, soil health, and ecosystem ecology. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project has provided research opportunities for one postdoc (Ben Hafner, root exudates), three graduate students (Dave Frey, researching soil respiration and root production; Stephanie Freund, studying plant nitrogen uptake, and Alyssa de Villiers studying DOM characterizations), as well as five undergraduates on the 2023 field & lab crew (Katherine Cabral, Sachi Srivastava, Sofia Mendez Bickham, Lena Cenegotitabengoa, and Daniel Dixon), and two technicians (Matthew Hecking and Jacob Scharfetter). It also supported the presentations by two project participants at the annual meeting of the Ecological Society of America in Portland, Oregon: one graduate student (Dave Frey) and an undergraduate he mentored the previous year (Eden Kebede). How have the results been disseminated to communities of interest?We have shared project results at several major national and international conferences during 2023, including the Ecological Society of America (two talks), the Soil Science Society of America (one talk), and the Ecological Society of Germany, Austria, and Switzerland (one talk). What do you plan to do during the next reporting period to accomplish the goals?During 2024, we plan to complete analytical measurements of plant, soil, and microbial carbon and nitrogen content (objectives 1 & 2), root exudate composition (LC-MS), and conduct batch sorption studies assessing DOM sorption onto surface mineral soil material. All four objectives will require substantial data QA/QC and statistical analysis, and manuscript preparation. We anticipate submitting at least two manuscripts by the end of 2024 on objectives 2 and 3.

Impacts
What was accomplished under these goals? During 2023, we completed this award's planned major tasks largely as planned. The thirteenth year of amendments were applied to our nitrogen- by pH manipulation experiment, replicated in six forest stands (3 primary forest, 3 secondary forest) near Ithaca, NY. Each stand contains four 40 x 40 m plots used to characterize tree growth and soil properties. Treatments are applied to 60 x 60 m areas consisting of the central plots with 10 m treated buffer. Treatments consist of two nitrogen additions at 50 kg N per hectare per year, one selected to raise soil pH (sodium nitrate) and one to acidify (ammonium sulfate). A third treatment uses elemental sulfur to acidify without nitrogen, and the fourth plots serve as controls. For Objective 1, assessing whether N and pH have altered microbial biomass and soil organic matter (SOM) storage into light (POM) and heavy (MAOM) pools, we quantitatively resampled SOM by soil depth (forest floor, 0-3, 3-10, 10-20 cm) in June & July, 2022 in all 24 forest plots. During 2023, we completed soil processing (sieving, grinding, weighting, etc.) and a range of lab measurements on 360 samples (24 plots x 5 locations/plot x 3 depths/location) to quantify soil C, and N, and their isotopic composition. As a second approach to study how N x pH treatments alter the formation of POM and MAOM, in October, 2022, we initiated a litter decomposition experiment with isotopically distinct leaf litter. For this experiment, we deployed replicated sets of ~0.1 m^2 blocks (five sets of three blocks per plot) that replaced that year's leaf litter with corn leaf litter, selected to serve as an inexpensive and abundant decomposition substrate with a distinctive carbon isotopic composition that can be traced into newly formed POM and MAOM in blocks to be destructively sampled 1, 2, and 5 years after deployment. During October, 2023, we conducted the first set of samplings, carefully extracting 360 samples and returning them to the lab for drying, weighing, and preparation for isotope analysis. For Objective 2, assessing whether N and pH have altered aboveground plant growth, in August and September 2022 we completed a full re-inventory of the diameter of all trees > 9.5 cm diameter. Aboveground litterfall was also collected from all plots during autumn 2022, with an additional overwinter litterfall collection planned for early spring 2023. An additional suite of measurements of the N content of these tissues (wood, bark, litterfall) and in newly produced roots (below) will allow estimates ecosystem-scale measurements of plant nitrogen uptake, to be used to assess the fate and efficiency of the applied N, as well as the belowground C expended by plants to take up this N. In 2023, we added further information to the plant-level N budget by collecting canopy foliage from the 3-4 dominant species on each plot for analysis of N content. We also conducted a suite of measurements of root-level N uptake for the most dominant species on the primary (sugar maple) and secondary (red maple) forest plots. For Objective 3, assessing N x pH effects on plant C allocation belowground, annual soil respiration measurements were compiled across all 24 plots. Root biomass measurements are under way, collected as part of the soil sampling efforts described in Objective 1, and measurements of root production into root ingrowth cores have been collected, and were picked, dried, and weighed during 2023. We also completed an additional study of soil heterotrophic respiration using all of the soil samples collected in Objective 1, that complement the field measurements of soil respiration, and allow a novel partitioning of soil respiration into heterotrophic and root-related respiration components. Last, in situ root exudate collections were successfully collected from six stands in 2023. For Objective 4, assessing N x pH effects on the composition and sorption of dissolved organic matter (DOM), sample processing began during fall 2022 to extract DOM from soil samples collected as part of Objective 1. Composition of the water-extractable DOM fraction < 0.2 µm has been evaluated using pH, nitrate, ammonium, aluminum, phosphate, total organic carbon, total nitrogen, and a suite of optical properties (SUVA254 for aromaticity, slope ratio for molecular weight, excitation-emission matrices (EEMs) for humification index, biological index, and fluorescence index). Together, this substantial body of field and lab work has the project largely on schedule.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: Frey, D.W., Goodale, C.L. Disentangling nitrogen's role as a limiting nutrient and acidifier: nutrient nitrogen availability, not acidification, suppresses soil respiration. 2023. Abstract 120-2. Ecological Society of America Annual Meeting, Portland, OR, USA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: Kebede, E, DW Frey, and CL Goodale. Digging deeper: contrasting the response of decomposition to nitrogen and acidity at different soil depths. Abstract COS 97-6 ESA Portland, OR, Aug. 2023
• Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: Frey, D.W., Hecking, M., Goodale, C.L. Liming alters fine root dynamics and spurs forest floor carbon accumulation in a mixed temperate forest. 2023. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America International Annual Meeting, St. Louis, MO, USA.
• Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: Hafner, BD, WL King, JB Scharfetter, g D Frey, G Gomer, CL Goodale, and TL Bauerle. Effects of nitrogen availability, pH, tree size and season on tree carbon allocation to root exudation. Gf�, Annual Meeting of the Ecological Society of Germany, Austria, and Switzerland. Leipzig, Germany, Sept. 2023

Progress 01/01/22 to 12/31/22

Outputs
Target Audience:The target audience is primarily soil- and forest scientists involved forest carbon management, soil health, and ecosystem ecology. Changes/Problems:We made two substantial additions and one moderate change to our planned work. The two additional studies include (1) initiating measurements of tissue N content to allow ecosystem-scale measurements of plant N uptake, and (2) measuring soil heterotrophic respiration (CO2 from decomposition in the absence of plant roots) by treatment and soil depth. The moderate change involved application of isotopically labeled litter to our field experiment to assess treatment effects on SOM formation. We originally planned to generate and deploy 13C-labeled maple leaf litter, to assess N and pH effects on POM and MAOM production. This approach appealed because maple leaf litter reflects forest composition, but expenses involved would have limited generation of material to only a small amount of material unlikely to provide sufficient replication when decomposed in the field, originally planned as just two replicate subplots/plot in three stands. Instead, we deployed abundant and inexpensive corn litter, with its naturally distinct 13C composition, as three sets of harvestable deployments (over 3 years) in each of five subplots in all four plots in all six stands (n = 360 total, 120/year). This vastly expanded replication both within and across stands greatly increases the likelihood of detecting treatment effects on POM and MAOM production. What opportunities for training and professional development has the project provided?This project has provided research opportunities for one postdoc (Ben Hafner, root exudates), three graduate students (Dave Frey researching soil respiration and root production; Stephanie Freund studying plant nitrogen uptake; and Alyssa de Villiers studying DOM characterizations, respectively), as well as four undergraduates on the 2022 summer field crew (Katherine Volquez; Phil Whorisky; Sofia Mendez Bickham) and an additional undergraduate (Eden Kebede) conducting an independent research project with the mentorship of one of the project's graduate students (Dave Frey). How have the results been disseminated to communities of interest?During 2022, early results on tree growth responses were disseminated though a presentation by Dave Frey at the 2022 Ecological Society of America annual meeting in Montreal, Quebec. What do you plan to do during the next reporting period to accomplish the goals?During 2023, we plan to complete lab analyses of soil carbon and nitrogen content (objectives 1 & 2), and to conduct measurements of root exudates in additional forest stands (objective 3). We further aim to characterize a range of soil and DOM properties (objective 4). All four objectives will be subject to substantial QA/QC and statistical analyses prior to manuscript preparation.

Impacts
What was accomplished under these goals? During 2022, we completed this award's planned major tasks largely as proposed in both content and timing, with a range of sampling activities conducted at a nitrogen- by pH manipulation experiment replicated in six forest stands (3 primary forest, 3 secondary forest) near Ithaca, NY. Each stand contains four 40 x 40 m plots used to characterize tree growth and soil properties. Treatments are applied to 60 x 60 m areas consisting of the central plots with 10 m buffer. Treatments consist of two nitrogen additions at 50 kg N per hectare per year, one selected to raise soil pH (sodium nitrate) and one to acidify (ammonium sulfate). A third treatment uses elemental sulfur to acidify without nitrogen, and the fourth plots serve as controls. For Objective 1, assessing whether N and pH have altered microbial biomass and soil organic matter (SOM) storage into light (POM) and heavy (MAOM) pools, we quantitatively resampled SOM by soil depth (forest floor, 0-3, 3-10, 10-20 cm) in June & July, 2022 in all 24 forest plots. Lab measurements are in progress during winter 2022-23 to quantify soil C, N, and S content, to complete microbial biomass measurements, and to partition soils into light and heavy SOM fractions. As a second approach to study how N x pH treatments alter the formation of POM and MAOM, in October we initiated a litter decomposition experiment. For this experiment, we deployed replicated sets of ~0.1 m^2 blocks (five sets of three blocks per plot) that replaced that year's leaf litter with corn leaf litter, selected to serve as an inexpensive and abundant decomposition substrate with a distinctive carbon isotopic composition that can be traced into newly formed POM and MAOM in blocks to be destructively sampled 1, 2, and 5 years after deployment. For Objective 2, assessing whether N and pH have altered aboveground plant growth, in August and September, 2022, we completed a full re-inventory of the diameter of all trees > 9.5 cm diameter. Data analysis of growth responses are under way. Aboveground litterfall was also collected from all plots during autumn 2022, with an additional overwinter litterfall collection planned for early spring 2023. An additional suite of measurements of the N content of these tissues (wood, bark, litterfall) and in newly produced roots (below) will allow estimates ecosystem-scale measurements of plant nitrogen uptake, to be used to assess the fate and efficiency of the applied N, as well as the belowground C needed to take up this N. For Objective 3, assessing N x pH effects on plant C allocation belowground, annual soil respiration measurements were compiled across all 24 plots. Root biomass measurements are under way, collected as part of the soil sampling efforts described in Objective 1, and measurements of root production into root ingrowth cores have been collected, with processing and analyses in progress. By leveraging an Cornell-based opportunity for supported undergraduate research, we also completed an additional study of soil heterotrophic respiration using all of the soil samples collected in Objective 1, that will complement and help interpret the field measurements of soil respiration. Last, an additional particularly challenging set of in situ root exudate collections were successfully piloted in two of the six stands, with additional measurements anticipated in year 2. For Objective 4, assessing N x pH effects on the composition and sorption of dissolved organic matter (DOM), sample processing began during fall 2022 to extract DOM from soil samples collected as part of Objective 1. Together, this substantial body of completed and continuing field and lab work has the project on schedule to complete proposed measurements.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: Frey, D.W., Goodale, C.L. Roles of nitrogen and soil pH in aboveground biomass production in mixed temperate forests in central New York, USA. 2022. Ecological Society of America and Canadian Society of Ecology and Evolution Joint Meeting, Montreal, QC, Canada.