title: Nitrogen Critical Loads for an Alpine Meadow Ecosystem on the Tibetan Plateau.
abstract: Increasing atmospheric nitrogen (N) deposition has the potential to alter plant diversity and thus the function and stability of terrestrial ecosystems. N-limited alpine ecosystems are expected to be particularly susceptible to increasing N deposition. However, little is known about the critical loads and saturation thresholds of ecosystem responses to increasing N deposition on the Tibetan Plateau, despite its importance to ecosystem management. To evaluate the N critical loads and N saturation thresholds in an alpine ecosystem, in 2010, we treated an alpine meadow with five levels of N addition (0, 10, 20, 40, and 80 kg N ha(-1) year(-1)) and characterized plant and soil responses. The results showed that plant species richness and diversity index did not statistically vary with N addition treatments, but they both changed with years. N addition affected plant cover and aboveground productivity, especially for grasses, and soil chemical features. The N critical loads and saturation thresholds, in terms of plant cover and biomass change at the community level, were 8.8-12.7 and 50 kg N ha(-1) year(-1) (including the ambient N deposition rate), respectively. However, pronounced changes in soil inorganic N and net N mineralization occurred under the 20 and 40 kg N ha(-1) year(-1) treatments. Our results indicate that plant community cover and biomass are more sensitive than soil to increasing N inputs. The plant community composition in alpine ecosystems on the Qinghai-Tibetan Plateau may change under increasing N deposition in the future.
authors.affiliation: Lhasa National Ecological Research Station, Key Laboratory of Ecosystem Network Observation and Modelling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11A, Datun Road, Chaoyang District, Beijing, 100101, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Ning
authors.initials: N
authors.lastname: Zong
authors.affiliation: Lhasa National Ecological Research Station, Key Laboratory of Ecosystem Network Observation and Modelling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11A, Datun Road, Chaoyang District, Beijing, 100101, China. shipl@igsnrr.ac.cn.
authors.forename: Peili
authors.initials: P
authors.lastname: Shi
authors.affiliation: Key Laboratory of Ecosystem Network Observation and Modelling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, 100101, China.
authors.forename: Minghua
authors.initials: M
authors.lastname: Song
authors.affiliation: Lhasa National Ecological Research Station, Key Laboratory of Ecosystem Network Observation and Modelling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11A, Datun Road, Chaoyang District, Beijing, 100101, China.
authors.forename: Xianzhou
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Nanjing Agricultural Institute of Jiangsu Hilly Region, Nanjing, 210046, Jiangsu, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Jiang
authors.affiliation: Lhasa National Ecological Research Station, Key Laboratory of Ecosystem Network Observation and Modelling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11A, Datun Road, Chaoyang District, Beijing, 100101, China.|University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Xi
authors.initials: X
authors.lastname: Chai
mesh_terms: D018533:Biomass; D017753:Ecosystem; D065948:Grassland; D009584:Nitrogen / Q000032:analysis*; D010944:Plants; D006109:Poaceae / Q000502:physiology; D012987:Soil / Q000737:chemistry; D018609:Tibet
chemical_list: D012987:Soil; D009584:Nitrogen
keywords: Alpine meadow; Nitrogen critical loads; Nitrogen deposition; Plant community composition; Qinghai-Tibetan Plateau; Soil characteristics