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Soil carbon fractions in grasslands respond differently to various levels of nitrogen enrichments |
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| Authors: | Bing Song Shuli Niu Linghao Li Lixia Zhang Guirui Yu |
| Institution: | 1. Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11A, Datun Road, Chaoyang District, Beijing, 100101, China 2. University of Chinese Academy of Sciences, No.19A Yuquan Road, Beijing, 100049, China 3. State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, No.20 Nanxincun, Xiangshan, Beijing, 100093, China 4. Key Laboratory of Plant Stress Biology, College of Life Sciences, Henan University, Jin Ming Avenue, Kaifeng, Henan, 475004, China |
| Abstract: | Background and AimsSoil 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.MethodsWe 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.ResultsThe 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.ConclusionsOur 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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