{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/127367"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/127367","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Use of 15N2 for direct measurement of free-living N2 fixation","abstract":"The use of 15N-labeled dinitrogen (15N2) affords the only direct means of measuring free-living nitrogen fixation (FLNF); however, progress in utilizing this approach has been impeded by methodological limitations and a lack of standardization regarding soil sampling, storage, and incubation. Such methodological constraints, including the presence of nitrogenous contaminants, a lack of atmospheric uniformity, and incomplete description of procedural details, are eliminated with a technique comprehensively described herein, which involves circulating 15N2 generated by hypobromite oxidation through a closed system that includes chemical (sulfuric acid-potassium permanganate) and cryogenic (isopentane-liquid N2) traps for atmospheric purification and an incubation chamber consisting of a desiccator equipped with a pressure gauge. Studies to evaluate the circulation system described showed that a uniform atmosphere was readily achieved with a 10 L desiccator by pumping for 30 min and that both chemical and cryogenic traps were necessary to ensure complete (98.8–99.6%) removal of gaseous contaminants subject to physicochemical retention by sterilized soil samples. The method proposed was successfully demonstrated in detecting the stimulatory effect of organic carbon (C) on FLNF in active soils and was subsequently utilized in a series of studies to systematically evaluate and standardize soil sampling, storage, and incubation parameters for optimizing isotopic measurement of this process. In these studies, incubations were conducted using four Illinois soils with respect to sampling depth, storage condition and period, surface exposure, moisture content, carbon source and pH, phosphorus (P) amendment, and incubation period. Among the major findings, diazotrophic activity was greatest with surface (0−7.5 cm) sampling, and storage effects were minimized when field-moist samples were kept for ≤ 1 d at room temperature (25°C) or in a refrigerator (5°C) with or without sieving (< 2 mm). In the presence of exogenous C (4 mg C g−1 dry soil), the rate of 15N2 fixation was maximized at ≥ 200% water-holding capacity and with a 3-d incubation period. A divergent preference regarding the form of organic C amendment was observed for soil samples collected before and after a 6-month interval, with simple sugars being preferred in the spring and organic acids in the fall. By standardizing several key parameters pertinent to the measurement of FLNF using the 15N2 method previously developed, the work reported can help clarify the ecological importance and agricultural potential of a process once believed to be a major source of soil N.","abstract_html":"The use of 15N-labeled dinitrogen (15N2) affords the only direct means of measuring free-living nitrogen fixation (FLNF); however, progress in utilizing this approach has been impeded by methodological limitations and a lack of standardization regarding soil sampling, storage, and incubation. Such methodological constraints, including the presence of nitrogenous contaminants, a lack of atmospheric uniformity, and incomplete description of procedural details, are eliminated with a technique comprehensively described herein, which involves circulating 15N2 generated by hypobromite oxidation through a closed system that includes chemical (sulfuric acid-potassium permanganate) and cryogenic (isopentane-liquid N2) traps for atmospheric purification and an incubation chamber consisting of a desiccator equipped with a pressure gauge. Studies to evaluate the circulation system described showed that a uniform atmosphere was readily achieved with a 10 L desiccator by pumping for 30 min and that both chemical and cryogenic traps were necessary to ensure complete (98.8–99.6%) removal of gaseous contaminants subject to physicochemical retention by sterilized soil samples. The method proposed was successfully demonstrated in detecting the stimulatory effect of organic carbon (C) on FLNF in active soils and was subsequently utilized in a series of studies to systematically evaluate and standardize soil sampling, storage, and incubation parameters for optimizing isotopic measurement of this process. In these studies, incubations were conducted using four Illinois soils with respect to sampling depth, storage condition and period, surface exposure, moisture content, carbon source and pH, phosphorus (P) amendment, and incubation period. Among the major findings, diazotrophic activity was greatest with surface (0−7.5 cm) sampling, and storage effects were minimized when field-moist samples were kept for ≤ 1 d at room temperature (25°C) or in a refrigerator (5°C) with or without sieving (&lt; 2 mm). In the presence of exogenous C (4 mg C g−1 dry soil), the rate of 15N2 fixation was maximized at ≥ 200% water-holding capacity and with a 3-d incubation period. A divergent preference regarding the form of organic C amendment was observed for soil samples collected before and after a 6-month interval, with simple sugars being preferred in the spring and organic acids in the fall. By standardizing several key parameters pertinent to the measurement of FLNF using the 15N2 method previously developed, the work reported can help clarify the ecological importance and agricultural potential of a process once believed to be a major source of soil N.","abstract_has_math":false,"creators":["Zhou, Qianchen"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"M.S.","degree_level":"Thesis","degree_discipline":"Natural Res & Env Sciences","degree_department":null,"school":null,"contributors":["Mulvaney, Richard L"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024-11-26","date_published":"2024-11-26","updated_at":"2026-07-22T22:25:03Z","subjects":["Biological N2 Fixation","Free-ling N2 Fixation","15n2 Incubation"],"languages":["eng","en"],"rights":["Copyright 2024 Qianchen Zhou"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/2142/127367","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Mulvaney, Richard L"]},{"key":"dc:creator","label":"Author","values":["Zhou, Qianchen"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2024-11-26","2024-12"]},{"key":"dc:type","label":"Dc Type","values":["text","Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Natural Res & Env Sciences"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Thesis"]},{"key":"thesis:degree_name","label":"Degree Name","values":["M.S."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Biological N2 Fixation","Free-ling N2 Fixation","15n2 Incubation"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng","en"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2024 Qianchen Zhou"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://hdl.handle.net/2142/127367"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["The use of 15N-labeled dinitrogen (15N2) affords the only direct means of measuring free-living nitrogen fixation (FLNF); however, progress in utilizing this approach has been impeded by methodological limitations and a lack of standardization regarding soil sampling, storage, and incubation. Such methodological constraints, including the presence of nitrogenous contaminants, a lack of atmospheric uniformity, and incomplete description of procedural details, are eliminated with a technique comprehensively described herein, which involves circulating 15N2 generated by hypobromite oxidation through a closed system that includes chemical (sulfuric acid-potassium permanganate) and cryogenic (isopentane-liquid N2) traps for atmospheric purification and an incubation chamber consisting of a desiccator equipped with a pressure gauge. Studies to evaluate the circulation system described showed that a uniform atmosphere was readily achieved with a 10 L desiccator by pumping for 30 min and that both chemical and cryogenic traps were necessary to ensure complete (98.8–99.6%) removal of gaseous contaminants subject to physicochemical retention by sterilized soil samples. The method proposed was successfully demonstrated in detecting the stimulatory effect of organic carbon (C) on FLNF in active soils and was subsequently utilized in a series of studies to systematically evaluate and standardize soil sampling, storage, and incubation parameters for optimizing isotopic measurement of this process. In these studies, incubations were conducted using four Illinois soils with respect to sampling depth, storage condition and period, surface exposure, moisture content, carbon source and pH, phosphorus (P) amendment, and incubation period. Among the major findings, diazotrophic activity was greatest with surface (0−7.5 cm) sampling, and storage effects were minimized when field-moist samples were kept for ≤ 1 d at room temperature (25°C) or in a refrigerator (5°C) with or without sieving (< 2 mm). In the presence of exogenous C (4 mg C g−1 dry soil), the rate of 15N2 fixation was maximized at ≥ 200% water-holding capacity and with a 3-d incubation period. A divergent preference regarding the form of organic C amendment was observed for soil samples collected before and after a 6-month interval, with simple sugars being preferred in the spring and organic acids in the fall. By standardizing several key parameters pertinent to the measurement of FLNF using the 15N2 method previously developed, the work reported can help clarify the ecological importance and agricultural potential of a process once believed to be a major source of soil N.","Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2026-12-01","The student, Qianchen Zhou, accepted the attached license on 2024-11-25 at 16:23.","The student, Qianchen Zhou, submitted this Thesis for approval on 2024-11-25 at 16:44.","This Thesis was approved for publication on 2024-11-26 at 08:12.","DSpace SAF Submission Ingestion Package generated from Vireo submission #21389 on 2025-03-28 at 14:43:25"]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Use of 15N2 for direct measurement of free-living N2 fixation"]}]}],"canonical_facts":{"dc:contributor":["Mulvaney, Richard L"],"dc:creator":["Zhou, Qianchen"],"dc:date":["2024-11-26","2024-12"],"dc:description":["The use of 15N-labeled dinitrogen (15N2) affords the only direct means of measuring free-living nitrogen fixation (FLNF); however, progress in utilizing this approach has been impeded by methodological limitations and a lack of standardization regarding soil sampling, storage, and incubation. Such methodological constraints, including the presence of nitrogenous contaminants, a lack of atmospheric uniformity, and incomplete description of procedural details, are eliminated with a technique comprehensively described herein, which involves circulating 15N2 generated by hypobromite oxidation through a closed system that includes chemical (sulfuric acid-potassium permanganate) and cryogenic (isopentane-liquid N2) traps for atmospheric purification and an incubation chamber consisting of a desiccator equipped with a pressure gauge. Studies to evaluate the circulation system described showed that a uniform atmosphere was readily achieved with a 10 L desiccator by pumping for 30 min and that both chemical and cryogenic traps were necessary to ensure complete (98.8–99.6%) removal of gaseous contaminants subject to physicochemical retention by sterilized soil samples. The method proposed was successfully demonstrated in detecting the stimulatory effect of organic carbon (C) on FLNF in active soils and was subsequently utilized in a series of studies to systematically evaluate and standardize soil sampling, storage, and incubation parameters for optimizing isotopic measurement of this process. In these studies, incubations were conducted using four Illinois soils with respect to sampling depth, storage condition and period, surface exposure, moisture content, carbon source and pH, phosphorus (P) amendment, and incubation period. Among the major findings, diazotrophic activity was greatest with surface (0−7.5 cm) sampling, and storage effects were minimized when field-moist samples were kept for ≤ 1 d at room temperature (25°C) or in a refrigerator (5°C) with or without sieving (< 2 mm). In the presence of exogenous C (4 mg C g−1 dry soil), the rate of 15N2 fixation was maximized at ≥ 200% water-holding capacity and with a 3-d incubation period. A divergent preference regarding the form of organic C amendment was observed for soil samples collected before and after a 6-month interval, with simple sugars being preferred in the spring and organic acids in the fall. By standardizing several key parameters pertinent to the measurement of FLNF using the 15N2 method previously developed, the work reported can help clarify the ecological importance and agricultural potential of a process once believed to be a major source of soil N.","Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2026-12-01","The student, Qianchen Zhou, accepted the attached license on 2024-11-25 at 16:23.","The student, Qianchen Zhou, submitted this Thesis for approval on 2024-11-25 at 16:44.","This Thesis was approved for publication on 2024-11-26 at 08:12.","DSpace SAF Submission Ingestion Package generated from Vireo submission #21389 on 2025-03-28 at 14:43:25"],"dc:format":["application/pdf"],"dc:identifier":["https://hdl.handle.net/2142/127367"],"dc:language":["eng","en"],"dc:rights":["Copyright 2024 Qianchen Zhou"],"dc:subject":["Biological N2 Fixation","Free-ling N2 Fixation","15n2 Incubation"],"dc:title":["Use of 15N2 for direct measurement of free-living N2 fixation"],"dc:type":["text","Thesis"],"thesis:degree_discipline":["Natural Res & Env Sciences"],"thesis:degree_level":["Thesis"],"thesis:degree_name":["M.S."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:25:03Z"}