Abstract
Background and Aims
Soil contains many different C fractions which have diverse physical and chemical compositions. Examining these differential soil C fractions in response to N enrichment is helpful for better understanding soil C changes under the predominantly increasing N deposition. In this study, we used a field N addition experiment in a grassland to explore the effects of various N enrichment levels on soil C fractions.
Methods
We conducted a field manipulative experiment which used a Latin square design with six N addition levels of 0, 2, 4, 8, 16 and 32 g N m−2 year−1 since 2003 in a semiarid grassland in northern China. Soil samples were collected in August (when plants have the greatest biomass), 2011. We measured C and N concentrations in soil light fraction, microbial biomass, extractable organic matter, heavy fraction, and total soil C and N.
Results
The results showed that total soil C and N, and heavy fraction C and N were not significantly affected by N addition after 9 years of treatments. In contrast, different N enrichment levels changed soil light fraction C and N, ranging from 4.3 to 27.7 % and 3.3–30.0 %, respectively. Moreover, both light fraction C and N had a nonlinear relationship with N addition rates, and the threshold for N-induced change in light fraction C and N was near 16 g N m−2 year−1 in this semiarid grassland. Increases of soil light fraction C and N primarily resulted from changes in biotic (N-stimulated aboveground biomass) and abiotic (soil temperature, moisture and pH) factors under N enrichment. Soil microbial biomass exponentially declined with increasing N, but extractable organic C showed a positive linear response to N enrichment rates. Changes in microbial biomass C and extractable organic C were primarily due to the reduced soil pH under N addition.
Conclusions
Our findings suggest that various soil C fractions differentially respond to elevated N, because different sets of biotic and abiotic factors regulate those fractions under N enrichment.
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Acknowledgments
The authors thank Xin Li, Shihuan Song, Naili Zhang, and Changhui Wang for their help in field measurement, instrument support, and laboratory analysis. We thank the staff of Duolun Restoration Ecology Experimentation and Demonstration Station. This study was financially supported by National Natural Science Foundation of China (31000227, 31290221), and Thousand Youth Talents Plan Project.
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Song, B., Niu, S., Li, L. et al. Soil carbon fractions in grasslands respond differently to various levels of nitrogen enrichments. Plant Soil 384, 401–412 (2014). https://doi.org/10.1007/s11104-014-2219-1
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DOI: https://doi.org/10.1007/s11104-014-2219-1