J Plant Ecol ›› 2010, Vol. 3 ›› Issue (3): 201-207 .DOI: 10.1093/jpe/rtq023

• Research Articles • Previous Articles     Next Articles

Natural 15N abundance in soils and plants in relation to N cycling in a rangeland in Inner Mongolia

Yuqing Xu1,2,*, Jicheng He3, Weixin Cheng2,4, Xuerong Xing2 and Linghao Li2   

  1. 1 National Climate Center, China Meteorological Administration, 46 South Zhongguancun Avenue Haidian, Beijing 100081, China; 2 State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, the Chinese Academy of Sciences, 20 Nanxincun, Xiangshan, Beijing 100093, China; 3 Energy Saving, Environmental Protection and Occupational Safety and Health Research Institute, China Academy of Railway Sciences, 2 Daliushulu, Beijing 100081, China; 4 Department of Environmental Studies, University of California, 1156 High Street, Santa Cruz, CA 95064, USA
  • Received:2010-01-17 Accepted:2010-07-18 Published:2010-08-19
  • Contact: Xu, Yuqing

Natural 15N abundance in soils and plants in relation to N cycling in a rangeland in Inner Mongolia

Abstract: Aims Natural 15 N abundance provides integrated information about nitrogen (N) input, transformation and output, indirectly reflecting N cycling traits within terrestrial ecosystems. However, relationships between natural 15 N abundance and N cycling processes are poorly understood in China. Here, our primary objectives were to (i) examine the effects of grazing at varying levels of intensity on δ 15 N of soils and plants in a semi-arid grassland; (ii) detect the relationships between δ 15 N of soils and four major N cycling processes (i.e. mineralization, nitrification, denitrification and ammonia volatilization); and (iii) determine whether δ 15 N of soils can be used as an indicator of N cycling in this semi-arid grassland.
Methods The field experiment was conducted within the long-term (17-year) grazing enclosures in a semi-arid grassland in Inner Mongolia. Five grazing intensities (0.00, 1.33, 2.67, 4.00 and 5.33 sheep ha-1) were designed. δ 15 N values of topsoils (0–10 cm), surface soils (0–2 cm) and plants were measured in 2006. Differences in δ 15 N of soils and plants between the five grazing intensities were examined. Rates of four soil N cycling processes were measured periodically during the 2005 and 2006 growing seasons. The δ 15 N values of topsoils were linked to the four N cycling processes to investigate their relationships.
Important findings The δ 15 N values of topsoils (5.20–5.96‰) were substantially higher than the δ 15 N values of plants (2.51–2.93‰) and surface soils (1.44–2.92‰) regardless of grazing intensities. The 15 N-depleted N losses during microbial decomposition of organic matter in concert with the downward movement of residual substrate over time are the possible causes of higher δ 15 N values in topsoils than in surface soils. In addition, the δ 15 N values of topsoils were positively correlated with the δ 15 N values of both plants and surface soils. Grazing, especially the high-intensity grazing (5.33 sheep ha-1), resulted in a significant decrease in δ 15 N of surface soils. However, no statistically significant variations in δ 15 N of topsoils and plants were found in response to grazing. The δ 15 N values of topsoils exhibited significant dependence on the cumulative rates of NH 3 volatilization, net nitrification and denitrification in 2005 but not in 2006.

Key words: δ15N, NH3 volatilization, mineralization, nitrification, denitrification, grazing intensity, grassland

摘要:
Aims Natural 15 N abundance provides integrated information about nitrogen (N) input, transformation and output, indirectly reflecting N cycling traits within terrestrial ecosystems. However, relationships between natural 15 N abundance and N cycling processes are poorly understood in China. Here, our primary objectives were to (i) examine the effects of grazing at varying levels of intensity on δ 15 N of soils and plants in a semi-arid grassland; (ii) detect the relationships between δ 15 N of soils and four major N cycling processes (i.e. mineralization, nitrification, denitrification and ammonia volatilization); and (iii) determine whether δ 15 N of soils can be used as an indicator of N cycling in this semi-arid grassland.
Methods The field experiment was conducted within the long-term (17-year) grazing enclosures in a semi-arid grassland in Inner Mongolia. Five grazing intensities (0.00, 1.33, 2.67, 4.00 and 5.33 sheep ha-1) were designed. δ 15 N values of topsoils (0–10 cm), surface soils (0–2 cm) and plants were measured in 2006. Differences in δ 15 N of soils and plants between the five grazing intensities were examined. Rates of four soil N cycling processes were measured periodically during the 2005 and 2006 growing seasons. The δ 15 N values of topsoils were linked to the four N cycling processes to investigate their relationships.
Important findings The δ 15 N values of topsoils (5.20–5.96‰) were substantially higher than the δ 15 N values of plants (2.51–2.93‰) and surface soils (1.44–2.92‰) regardless of grazing intensities. The 15 N-depleted N losses during microbial decomposition of organic matter in concert with the downward movement of residual substrate over time are the possible causes of higher δ 15 N values in topsoils than in surface soils. In addition, the δ 15 N values of topsoils were positively correlated with the δ 15 N values of both plants and surface soils. Grazing, especially the high-intensity grazing (5.33 sheep ha-1), resulted in a significant decrease in δ 15 N of surface soils. However, no statistically significant variations in δ 15 N of topsoils and plants were found in response to grazing. The δ 15 N values of topsoils exhibited significant dependence on the cumulative rates of NH 3 volatilization, net nitrification and denitrification in 2005 but not in 2006.