title: Effects of root exudates of woody species on the soil anti-erodibility in the rhizosphere in a karst region, China.
abstract: BACKGROUND
  Rhizospheres, the most active interfaces between plants and soils, play a central role in the long-term maintenance of the biosphere. The anti-erodibility of soils (AES) regulated by the root exudates is crucial to the soil stability in the rhizospheres. However, scientists still debate (1) the key organic matter of the root exudates affecting the AES and (2) the interspecific variation of these root exudates.
  
  
  METHODS
  We used an incubation of soils to test the effects of the root exudates from eight woody plant species on the change in soil aggregation and identified the organic matter in these root exudates with gas chromatography-mass spectrometry (GC-MS) and biochemical methods. Furthermore, the relationships between the organic matter in the exudates and the AES in the rhizospheres of 34 additional tree species were analyzed.
  
  
  RESULTS
  The water-stable aggregates of the soils incubated with the root exudates increased by 15%-50% on average compared with control samples. The interspecific differences were significant. The root exudates included hundreds of specific organic matter types; hydrocarbon, total sugar, total amino acids, and phenolic compounds were crucial to the AES. These organic matter types could explain approximately 20-75% of the variation in the total effect of the root exudates on the AES, which was quantified based on the aggregate status, degree of aggregation, dispersion ratio, and dispersion coefficient.
  
  
  CONCLUSIONS
  The effects of the root exudates on the AES and the interspecific variation are as important as that of root density, litters, and vegetation covers. Many studies explored the effects of root density, litters, vegetation covers, and vegetation types on the AES, but little attention has been paid to the effects of the root exudates on the AES. Different plants secrete different relative contents of organic matter resulting in the variation of the effect of the root exudates on the AES. Our study quantified the causal relationships between the root exudates and the AES using modeling experiments in laboratory and field observations and indicated the interspecific variation of the AES and organic matter of the root exudates.
  
  
  CONCLUSIONS
  More organic compounds of the exudates related to the AES were recognized in this study. These results enhance the understanding of the soil stability at a slope and can be applied to ecosystem restoration.
authors.affiliation: School of Environmental Science and Engineering, Chang'an University , Xi'an , China.
authors.forename: Zhen Hong
authors.initials: ZH
authors.lastname: Wang
authors.affiliation: Water-affair Authority, Xifeng County , Guiyang , Guizhou , China.
authors.forename: Hong
authors.initials: H
authors.lastname: Fang
authors.affiliation: College of Forestry, Guizhou University , Guiyang , Guizhou , China.
authors.forename: Mouhui
authors.initials: M
authors.lastname: Chen
keywords: Aggregate status; Anti-erodibility of soils; Degree of aggregation; Dispersion ratio; Gas chromatograph-mass spectrometer; Interspecific differences; Karst; Micro-aggregates; Rhizosphere; Root exudates; Soil erosion; Soil incubation; Water-stable aggregates; Woody plants