J Plant Ecol ›› 2019, Vol. 12 ›› Issue (3): 550-563.DOI: 10.1093/jpe/rty047

• Research Articles • Previous Articles     Next Articles

Responses of plant 15N natural abundance and isotopic fractionation to N addition reflect the N status of a temperate steppe in China

Zhilu Sheng1, Yongmei Huang1,*, Kejian He2, Narigele Borjigin1, Hanyue Yang3, Huiying Chen1, Engui Li1, Xia Xu1 and Lei Duan3#br#   

  1. 1 State Key Laboratory of Earth Surface and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, No. 19, XinJieKouWai St., HaiDian District, Beijing 100875, China
    2 Key Laboratory of Atmospheric Environment and Processes in the Boundary Layer over the Low-Latitude Plateau Region, College of Resource and Environment, Yunnan University, No. 2, Cuihu North Road, Wuhua District, Kunming 650091,
    China
    3 State Key Laboratory of Environmental Simulation and Pollution Control, School of Environment, Tsinghua University, No. 30, Shuangqing Road, HaiDian District, Beijing 100084, China
    *Corresponding address. State Key Laboratory of Earth Surface and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, No. 19, XinJieKouWai St., HaiDian District, Beijing 100875, China. Tel: +86-10-58802348, Fax: +86-10-58802348, E-mail: ymhuang@bnu.edu.cn
  • Received:2018-05-04 Revised:2018-10-31 Accepted:2018-11-15 Online:2018-11-19 Published:2019-07-01

Abstract:

Aims

Elevated anthropogenic nitrogen (N) deposition could alter N status in temperate steppe. However, threshold observations of N status change from N limit to N saturation by far are not conclusive in these ecosystems. Research on the natural abundance of 15N (δ15N) could greatly help provide integrated information about ecosystem N status. The goal of this study was to investigate the suitability of measurements of δ15N of major ecosystem N pools and several key species, plant 15N fractionation, together with key vegetation and soil indicators in response to N fertilization as a tool to identify the N status in a temperate steppe in Inner Mongolia.

Methods

We carried out a N addition experiment during 2011–14 on a Stipa krylovii steppe in Inner Mongolia, Northern China. We investigated the response of several key N transformation processes, vegetation and soil properties to N addition. Aboveground biomass and belowground biomass (BGB) δ15N, root and foliar δ15N of three dominant species (Artemisia frigidaS. krylovii and Leymus chinensis), δ15N of soil total N and soil KCl-extractable NO3?-N were determined. The responses of isotope fractionation during plant N uptake and reallocation to N addition were also determined.

Important Findings

Our results suggest that the N addition rate of 5g N m?2 yr?1 could be regarded as threshold of early N saturation in this S. krylovii steppe as indicated by an increase in plant fractionation and a decrease in plant δ15N. When N input rate is >10 g N m–2 yr–1, increased N deposition can lead to an apparent reduction in species richness and BGB as well as an increase in NO3? in extractable soil pools <30-cm soil profile. With N addition, S. krylovii and A. frigida undergo earlier N status shift from N limitation toward N excess compared with L. chinensis, contributing to L. chinensis out-competing other species. Overall, this study provides a better understanding of N status change in temperate steppe based on isotope evidence and several other functional variables and contributes to predicting the responses of temperate steppe to future global N deposition scenario.

Key words: N deposition, 15N natural abundance, temperate steppe, N saturation