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Journal of Arid Land  2014, Vol. 6 Issue (4): 423-431    DOI: 10.1007/s40333-014-0063-z
Research Articles     
Artificial root exudates and soil organic carbon mineralization in a degraded sandy grassland in northern China
YongQing LUO1,2*, XueYong ZHAO1, Olof ANDRÉN1,3, YangChun ZHU1,2, WenDa HUANG1
1 Naiman Desertification and Farmland Research Station of the Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China;
2 University of Chinese Academy of Sciences, Beijing 100049, China;
3 Bjorklundavagen 3, SE-756 46 Uppsala, Sweden
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Abstract  Plant root exudates contain various organic and inorganic components that include glucose, citric and oxalic acid. These components affect rhizosphere microbial and microfaunal activities, but the mechanisms are not fully known. Studies concerned from degraded grassland ecosystems with low soil carbon (C) contents are rare, in spite of the global distribution of grasslands in need of restoration. All these have a high potential for carbon sequestration, with a reduced carbon content due to overutilization. An exudate component that rapidly decomposes will increase soil respiration and CO2 emission, while a component that reduces decomposition of native soil carbon can reduce CO2 emission and actually help sequestering carbon in soil. Therefore, to investigate root exudate effects on rhizosphere activity, citric acid, glucose and oxalic acid (0.6 g C/kg dry soil) were added to soils from three biotopes (grassland, fixed dune and mobile dune) located in Naiman, Horqin Sandy Land, Inner Mongolia, China) and subjected to a 24-day incubation experiment together with a control. The soils were also analyzed for general soil properties. The results show that total respiration without exudate addition was highest in grassland soil, intermediate in fixed dune and lowest in mobile dune soil. However, the proportion of native soil carbon mineralized was highest in mobile dune soil, reflecting the low C/N ratio found there. The exudate effects on CO2-C emissions and other variables differed somewhat between biotopes, but total respiration (including that from the added substrates) was significantly increased in all combinations compared with the control, except for oxalic acid addition to mobile dune soil, which reduced CO2-C emissions from native soil carbon. A small but statistically significant increase in pH by the exudate additions in grassland and fixed dune soil was observed, but there was a major decrease from acid additions to mobile dune soil. In contrast, electrical conductivity decreased in grassland and fixed dune soil and increased in mobile dune. Thus, discrete components of root exudates affected soil environmental conditions differently, and responses to root exudates in soils with low carbon contents can differ from those in normal soils. The results indicate a potential for, e.g., acid root exudates to decrease decomposition rate of soil organic matter in low carbon soils, which is of interest for both soil restoration and carbon sequestration.

Key wordssoil enzyme activity      saline soil      Haloxylon ammodendron      Reaumuria soongonica      Salsola passerina      Tamarix rarmosissima     
Received: 08 October 2013      Published: 12 August 2014

This work was financially supported by the National Natural Science Foundation of China (41071185, 31170413) and the National Basic Research Program of China (2011BAC07B02). Chinese Academy of Sciences has kindly granted Prof. Olof ANDRÉN a ‘Professorship for Senior International Scientists’ (Y229D91001), which made his participation possible.

Corresponding Authors: YongQing LUO     E-mail:
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YongQing LUO, XueYong ZHAO, Olof ANDRéN, YangChun ZHU, WenDa HUANG. Artificial root exudates and soil organic carbon mineralization in a degraded sandy grassland in northern China. Journal of Arid Land, 2014, 6(4): 423-431.

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