Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee Natural primary production mediates the efects of nitrogen and carbon addition on plant functional groups biomass and temporal stability in the Tibetan alpine steppe-meadow Tao Zhang a,b,c , Xiaopeng Chen d , Ruiying Guo a , A. Allan Degen e , Michael Kam e , Jingxue Zhao a , Ximing Wang a , Yanfu Bai a , Wenyin Wang a , Rui Zhang b , Yinfeng Li a , Yu Liu f , Ruijun Long a , Zhongkui Xie b,c , Zhanhuan Shang a, * a State Key Laboratory of Grassland Agro-ecosystems, School of Life Sciences, Lanzhou University, Lanzhou, 730000, China b Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, China c University of Chinese Academy of Sciences, Beijing, 100049, China d College of Animal Science and Veterinary Technology, Shanxi Agricultural University, Taigu, 030801, China e Desert Animal Adaptations and Husbandry, Wyler Department of Dryland Agriculture, Blaustein Institutes for Desert Research, Ben-Gurion University of Negev, Beer Sheva, 8410500, Israel f State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A & F University, Yangling, Shaanxi, 712100, China ARTICLEINFO Keywords: Alpine steppe-meadow Nitrogen addition Carbon addition Plant functional groups Primary production Community stability Northern Tibet ABSTRACT Background and aims: Extensive studies have been made on the efect of the addition of nitrogen (N) and organic carbon (C) on grasses, sedges and forbs of the alpine ecosystems; however, few such studies have been made on alpine plant communities and plant functional groups at extremely high altitudes. We questioned whether the addition of N and C, two important soil elements, would have diferent efects on plant functional groups and on the main plant species in an alpine steppe meadow ecosystem at an altitude of 4700 m. Methods: A two-factor completely randomized design study was used, with the addition of three levels of N (0, 50and100kgNha −1 ;ureaasNsource)andthreelevelsofC(0,60and120kgCha −1 ; sucrose as C source) and four replicates, each year from 2011−2014. Efects at the community, plant functional groups and species levels were examined in an alpine steppe meadow. Results and discussion: With N and C as a single additive, biomass of grasses increased while forbs decreased. Sedges remained unchanged with N addition and increased with C addition. These results may be due to competition among Stipa purpurea, Poa alpigena, Kobresia humilis and forbs for light resources. This efect could be explained by the increase in cover of the major gramineous species, Stipa purpurea, while the cover of the sedge, Kobresia humilis, tended to decrease or showed no change with N addition. High level of N addition alone produced highest biomass in a year of low natural primary production (without C and/or N addition). After the addition of N and C together, the biomass of the three plant functional groups did not change or even decreased compared with either C or N addition. Furthermore, C addition increased community stability but N addition did not. Conclusions: The efects of N and C addition on the biomass of plant functional groups were complicated by the interaction between N and C, as well as by a major efect of initial standing biomass. With the addition of both N and C, the biomass of grasses increased and forbs decreased, especially in low natural primary production years. With C as a single additive, the biomass of sedges increased as did community stability. Consequently, man- agement of plant biomass using N and/or C addition depends on both the plant functional group target and the species within the group, as well as the natural primary production. Predicting environmental factors that po- tentially afect primary production are crucial in a decision-making nutrient management system. https://doi.org/10.1016/j.agee.2020.107080 Received 2 March 2020; Received in revised form 16 June 2020; Accepted 10 July 2020 ⁎ Corresponding author. E-mail address: shangzhh@lzu.edu.cn (Z. Shang). Agriculture, Ecosystems and Environment 302 (2020) 107080 0167-8809/ © 2020 Elsevier B.V. All rights reserved. T