Dynamics of Soil Organic Carbon and Nitrogen Following Agricultural Abandonment in a Karst Region
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 Agricultural abandonment is regarded as a major driver of soil organic carbon (C) dynamics, but the mechanisms underlying the direction and magnitude of soil C dynamics following agricultural abandonment are poorly understood.
       Although lithology has been found to impact soil C content as a key component of the earth system surface, whether or not lithology controls the direction and magnitude of soil C dynamics following agricultural abandonment has rarely been investigated. It is also unclear whether the phenomenon (i.e., the patterns of soil C dynamics following agricultural abandonment differ between lithology types) exists in other regions.
       Southwest China is famous for contiguous karst area underlain by dolomite or limestone or their mixtures and characterized by the extremely fragile geological background and susceptibility to land degradation upon human disturbances, particularly agricultural activities. In the past, most of the degraded lands in the karst in southwest China have been under ecological restoration following agricultural abandonment either through natural regeneration (spontaneous succession) or through afforestation. However, the impacts of ecological restoration following agricultural abandonment on soil C sequestration have not been well evaluated at a regional scale.
       Using a space-for-time substitution approach, one hundred twenty-five sites from cropland, grassland, shrubland, and secondary forest were selected to represent different succession stages by a team from the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA). They investigated the dynamics of soil C and N contents during postagricultural succession and further analyzed the patterns of soil C and N dynamics differed between the two lithology types in a karst region, southwest China.
       The researchers found that both soil C and N contents were lowest in the cropland while highest in the forest. Due to significantly greater contents of soil C and N in the cropland and grassland underlain by limestone, the soil C and N contents were greater (P< 0.05) over limestone than over dolomite mainly. “Soil C and N contents increased significantly from cropland to forest over dolomite, while varied insignificantly among succession stages over limestone. Exchangeable calcium explained most of soil C and N variance.” said, the leader researcher Dejun Li at ISA. Besides, the team proposed that following agricultural abandonment, calcium level recovered due to decreased loss, which in turn resulted in recovery of soil C and N.
       This work was supported National Key Research and Development Program of China (2016YFC0502404), the National Key Basic Research Program of China (2015CB452703), the Chinese Academy of Sciences through its One-Hundred Talent Program to Dejun Li (Y523101030 and Y351025090), the National Natural Science Foundation of China (41571295), and the Science and Technology Service Network Initiative of the Chinese Academy of Sciences (KFJ-EW-STS-092).
       This study entitled “Dynamics of soil organic carbon and nitrogen following agricultural abandonment in a karst region” has been published online in Journal of Geophysical Research: Biogeosciences (25 Jan 2017, doi: 10.1002/2016JG003683). The details could be found at http://onlinelibrary.wiley.com/doi/10.1002/2016JG003683/full 

Contact: LI Dejun
       E-mail: dejunli@isa.ac.cn
       Institute of Subtropical Agriculture