Chinese Bulletin of Botany ›› 2018, Vol. 53 ›› Issue (1): 27-41.DOI: 10.11983/CBB17041

• RESEARCH ARTICLE • Previous Articles     Next Articles

Effects of Nitrogen Addition on Ecosystem CO2 Exchange in a Meadow Steppe, Inner Mongolia

Muqier Hasi1,2, Xueyao Zhang1,2, Guoxiang Niu1,2, Yinliu Wang1,2, Jianhui Huang1,*()   

  1. 1State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
    2College of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2017-03-09 Accepted:2017-05-08 Online:2018-01-01 Published:2018-08-10
  • Contact: Jianhui Huang

Abstract:

Increasing nitrogen deposition influences carbon sequestration in grassland ecosystems, but we have no consistent results on how it impacts the exchange of CO2 at the ecosystem level. As well, the impact of different types of N fertilizers and rates of N increase are not clear yet. This study aimed to evaluate the effect of N addition on ecosystem CO2 exchange and was performed in a meadow steppe in Erguna, Inner Mongolia. A field experiment compared two types of N fertilizers (urea and slow-release urea) with five N addition rates (0, 5.0, 10.0, 20.0 and 50.0 g N·m-2·a-1). At the start and middle stage of the growing season, N addition had weak and inhibitive effects on ecosystem CO2 exchange when precipitation was low, and significantly increased ecosystem CO2 exchange in the late growing season when precipitation was high. Both net ecosystem CO2 exchange and gross ecosystem photosynthesis increased significantly with N addition rate but showed a tendency of saturation when the N addition rate reached 10 g N·m-2·a-1. The two types of N fertilizers resulted in slightly different responses of ecosystem CO2 exchange: slow-release urea had a stronger positive effect at 5 g N·m-2·a-1 with no significant difference at other addition rates. Our study suggests that increasing N deposition has significant effects on carbon assimilation in this semi-arid grassland, but the direction and magnitude of effects are strongly affected by seasonal pattern and amount of precipitation. The effects of different types of N fertilizers (i.e., urea and slow-release urea) on ecosystem CO2 exchange may differ.

Key words: nitrogen addition, net ecosystem CO2 exchange, ecosystem respiration, gross ecosystem photosynthesis, meadow steppe