Greater impacts of reduced than oxidized nitrogen enrichment on plant diversity losses in a temperate grassland

Abstract Background Increasing atmospheric nitrogen (N) deposition is a major threat to plant diversity globally. Recent observations show that the reduced-to-oxidized (NHx/NOy) ratio of N deposition has been changing spatially and temporally. How and to what extent different N forms (i.e., NHx and...

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Main Authors: Suxian Ren, Tianci Huo, Xin Jing, Weixing Liu, Xiaowei Gou, Xun Sun, Ru Hou, Junyi Liang
Format: Article
Language:English
Published: SpringerOpen 2025-03-01
Series:Ecological Processes
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Online Access:https://doi.org/10.1186/s13717-025-00603-2
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author Suxian Ren
Tianci Huo
Xin Jing
Weixing Liu
Xiaowei Gou
Xun Sun
Ru Hou
Junyi Liang
author_facet Suxian Ren
Tianci Huo
Xin Jing
Weixing Liu
Xiaowei Gou
Xun Sun
Ru Hou
Junyi Liang
author_sort Suxian Ren
collection DOAJ
description Abstract Background Increasing atmospheric nitrogen (N) deposition is a major threat to plant diversity globally. Recent observations show that the reduced-to-oxidized (NHx/NOy) ratio of N deposition has been changing spatially and temporally. How and to what extent different N forms (i.e., NHx and NOy) influence grassland plant species loss are still unclear. Methods We employed a field manipulative experiment by using three N forms [i.e., Ca(NO3)2, NH4NO3, and (NH4)2SO4] with six N addition levels (0, 4, 8, 16, 24, 32 g N m−2 year−1) in a temperate grassland and conducted a greenhouse experiment culturing four plant species corresponding different plant functional groups under Ca(NO3)2 or (NH4)2SO4 addition. Results Results from our field experiment showed that the plant species loss rate was greater under NH4 +–N than NO3 −–N enrichment. Plant species loss was driven by light asymmetry under NO3 −–N enrichment, while it was co-driven by light asymmetry and soil acidification under NH4NO3 enrichment. Under NH4 +–N enrichment, light asymmetry, pH decrease, NH4 + toxicity, and metal toxicity jointly affected species loss. The greenhouse experiment provided direct evidence that legumes and forbs are more physiologically susceptible to NH4 +-induced toxicity than grasses. Conclusions Our results emphasize that N forms play a vital role in affecting grassland plant diversity. This suggests that regions with higher NHx enrichment may experience more severe plant diversity losses as N deposition continues to increase. Therefore, appropriate measures should be adopted to mitigate species losses.
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spelling doaj-art-4491a7e6efea49b582185357516a98e72025-08-20T03:41:12ZengSpringerOpenEcological Processes2192-17092025-03-0114111210.1186/s13717-025-00603-2Greater impacts of reduced than oxidized nitrogen enrichment on plant diversity losses in a temperate grasslandSuxian Ren0Tianci Huo1Xin Jing2Weixing Liu3Xiaowei Gou4Xun Sun5Ru Hou6Junyi Liang7Department of Grassland Resource and Ecology, College of Grassland Science and Technology, China Agricultural UniversityDepartment of Grassland Resource and Ecology, College of Grassland Science and Technology, China Agricultural UniversityState Key Laboratory of Herbage Improvement and Grassland Agro-Ecosystems, and College of Pastoral Agriculture Science and Technology, Lanzhou UniversityState Key Laboratory of Efficient Utilization of Arid and Semi-Arid Arable Land in Northern China, Hulunber Grassland Ecosystem National Observation and Research Station, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural SciencesDepartment of Grassland Resource and Ecology, College of Grassland Science and Technology, China Agricultural UniversityDepartment of Grassland Resource and Ecology, College of Grassland Science and Technology, China Agricultural UniversityDepartment of Mathematics, College of Science, China Agricultural UniversityDepartment of Grassland Resource and Ecology, College of Grassland Science and Technology, China Agricultural UniversityAbstract Background Increasing atmospheric nitrogen (N) deposition is a major threat to plant diversity globally. Recent observations show that the reduced-to-oxidized (NHx/NOy) ratio of N deposition has been changing spatially and temporally. How and to what extent different N forms (i.e., NHx and NOy) influence grassland plant species loss are still unclear. Methods We employed a field manipulative experiment by using three N forms [i.e., Ca(NO3)2, NH4NO3, and (NH4)2SO4] with six N addition levels (0, 4, 8, 16, 24, 32 g N m−2 year−1) in a temperate grassland and conducted a greenhouse experiment culturing four plant species corresponding different plant functional groups under Ca(NO3)2 or (NH4)2SO4 addition. Results Results from our field experiment showed that the plant species loss rate was greater under NH4 +–N than NO3 −–N enrichment. Plant species loss was driven by light asymmetry under NO3 −–N enrichment, while it was co-driven by light asymmetry and soil acidification under NH4NO3 enrichment. Under NH4 +–N enrichment, light asymmetry, pH decrease, NH4 + toxicity, and metal toxicity jointly affected species loss. The greenhouse experiment provided direct evidence that legumes and forbs are more physiologically susceptible to NH4 +-induced toxicity than grasses. Conclusions Our results emphasize that N forms play a vital role in affecting grassland plant diversity. This suggests that regions with higher NHx enrichment may experience more severe plant diversity losses as N deposition continues to increase. Therefore, appropriate measures should be adopted to mitigate species losses.https://doi.org/10.1186/s13717-025-00603-2Nitrogen depositionPlant diversityNitrogen formLight asymmetryAcidificationNH4 + toxicity
spellingShingle Suxian Ren
Tianci Huo
Xin Jing
Weixing Liu
Xiaowei Gou
Xun Sun
Ru Hou
Junyi Liang
Greater impacts of reduced than oxidized nitrogen enrichment on plant diversity losses in a temperate grassland
Ecological Processes
Nitrogen deposition
Plant diversity
Nitrogen form
Light asymmetry
Acidification
NH4 + toxicity
title Greater impacts of reduced than oxidized nitrogen enrichment on plant diversity losses in a temperate grassland
title_full Greater impacts of reduced than oxidized nitrogen enrichment on plant diversity losses in a temperate grassland
title_fullStr Greater impacts of reduced than oxidized nitrogen enrichment on plant diversity losses in a temperate grassland
title_full_unstemmed Greater impacts of reduced than oxidized nitrogen enrichment on plant diversity losses in a temperate grassland
title_short Greater impacts of reduced than oxidized nitrogen enrichment on plant diversity losses in a temperate grassland
title_sort greater impacts of reduced than oxidized nitrogen enrichment on plant diversity losses in a temperate grassland
topic Nitrogen deposition
Plant diversity
Nitrogen form
Light asymmetry
Acidification
NH4 + toxicity
url https://doi.org/10.1186/s13717-025-00603-2
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