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Acta Prataculturae Sinica ›› 2019, Vol. 28 ›› Issue (5): 163-170.DOI: 10.11686/cyxb2018409

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Short term effects on ecosystem CO2 exchange in a semi-arid grassland agro-pastoral ecotone, following differing levels of nitrogen application

DONG Xiao-xiao1, BO Yuan-chao1, SUN Jian-ping1,2, ZHANG Xiao-lin1, WANG Chang-hui2,*, DONG Kuan-hu1,*   

  1. 1.College of Animal Science and Technology, Shanxi Agricultural University, Taigu 030801, China;
    2.State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
  • Received:2018-06-22 Revised:2018-10-18 Online:2019-05-20 Published:2019-05-20
  • Contact: E-mail: dongkuanhu@sxau.edu.cn, wangch@ibcas.ac.cn

Abstract: This study investigated the short-term effects of different nitrogen (N) application rates in a semi-arid grassland ecosystem in an agro-pastoral ecotone in Youyu County, Shanxi Province, China. A randomized complete block experiment was set up with 8 nitrogen levels (0, 1, 2, 4, 8, 16, 24, and 32 g N·m-2, denoted N0, N1, N2, N4, N8, N16, N24, N32, respectively), and 6 replicates (48 plots in total). Ecosystem net CO2 exchange (NEE) and ecosystem respiration (ER) under the different treatments were monitored using the static chamber method, with a fixed base for the portable chamber located in each plot before the start of the growing season, and chamber dimensions 50 cm×50 cm×50 cm. Gross ecosystem CO2 capture was calculated from those primary data by difference, and was taken as gross ecosystem productivity (GEP). Nine measurements were undertaken at approximately two weekly intervals between June and September. Over this period, short-term N addition (except N32, which had a detrimental effect) significantly increased the net carbon uptake, with peak response seen in N16 and N24 treatments. The responses of ER and GEP to different N addition were more sensitive than NEE. There was a significant positive correlation between 10 cm soil temperature and ER (R2=0.319, P<0.0001), while the soil moisture for the upper 10 cm was significantly positively correlated with NEE (R2=0.420, P<0.0001) and was significantly negatively correlated with GEP (R2=0.202, P=0.0004). Therefore, short-term nitrogen addition increased the net carbon uptake of this semi-arid in the agro-pastoral ecotone, grassland ecosystem. Our study provides some reference data for grassland ecosystem carbon source/sink relationships in this region.

Key words: nitrogen addition levels, agro-pastoral ecotone, semi-arid grassland, ecosystem CO2 exchange