Pedosphere 24(2): 232--242, 2014
ISSN 1002-0160/CN 32-1315/P
©2014 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Patterns of soil 15N and total N and their relationships with environmental factors on the Qinghai-Tibetan Plateau
ZHOU Lei1,2, SONG Ming-Hua1, WANG Shao-Qiang1, FAN Jiang-Wen1, LIU Ji-Yuan1, ZHONG Hua-Ping1, YU Gui-Rui1, GAO Lu-Peng1, HU Zhong-Min1, CHEN Bin1, WU Wei-Xing1 and SONG Ting1
1Key Laboratory of Ecosystem Network Observation and Modelling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101 (China)
2 University of Chinese Academy of Sciences, Beijing 100049 (China)
ABSTRACT
      The patterns of soil nitrogen (N) isotope composition (δ15N) at large spatial and temporal scales and their relationships to environmental factors illustrate N cycle and sources of N, and are integrative indicators of the terrestrial N cycle and its response to global change. The objectives of this study were: i) to investigate the patterns of soil N content and natural abundance of 15N (δ15N) values in different ecosystem types and soil profiles on the Qinghai-Tibetan Plateau; ii) to examine the effects of climatic factors and soil characteristics on the patterns of soil N content and soil δ15N values; and iii) to test the relationship between soil δ15N values and soil C/N ratios across ecosystems and soil profiles. Soil profiles were sampled at 51 sites along two transects 1 875 km in length and 200 km apart and distributed in forest, meadow and steppe on the Qinghai-Tibetan Plateau. Each site was sampled every 10 cm from a soil depth of 0 to 40 cm and each sample was analyzed for soil N content and δ15N values. Our results indicated that soil N and δ15N values (0--40 cm) in meadows were much higher than in desert steppe. Soil N decreased with soil depth for each ecosystem, while variations of soil δ15N values along soil profiles were not statistically significant among most ecosystems but for mountain meadow, lowland meadow, and temperate steppe where soil δ15N values tended to increase with soil depth. The parabolic relationship between soil δ15N values and mean annual precipitation indicated that soil δ15N values increased with increasing precipitation in desert steppe up to 500 mm, and then decreased with increasing precipitation across all other ecosystems. Moreover, the parabolic relationship between δ15N values and mean annual temperature existed in all individual ecosystem types. Soil N and δ15N values (0--40 cm) increased with an increase in soil silt and clay contents. Furthermore, a threshold of C/N ratio of about 11 divided the parabolic relationship between soil δ15N values and soil C/N ratios into positive (C/N < 11) and negative (C/N > 11) parts, which was valid across all ecosystems and soil profiles. The large explanatory power of soil C/N ratios for soil δ15N values suggested that C and N concentrations, being strongly controlled by precipitation and temperature, were the primary factors determining patterns of soil δ15N on the Qinghai-Tibetan Plateau.
Key Words:  desert steppe, nitrogen isotope composition, nutrient availability, soil nitrogen
Citation: Zhou, L., Song, M. H., Wang, S. Q., Fan, J. W., Liu, J. Y., Zhong, H. P., Yu, G. R., Gao, L. P., Hu, Z. M., Chen, B., Wu, W. X. and Song, T. 2014. Patterns of soil 15N and total N and their relationships with environmental factors on the Qinghai-Tibetan Plateau. Pedosphere. 24(2): 232-242.
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