The direct and legacy effects of drying-rewetting cycles on active and relatively resistant soil carbon decomposition
Shuai Zhanga,b, Junjie Lina*, Peng Wangc, Biao Zhud*
  1. Chongqing Key Laboratory of Water Environment Evolution and Pollution Control in Three Gorges Reservoir, Chongqing Three Gorges University, Chongqing 404100, China
  2. College of environmental and resource sciences, Zhejiang University, Hangzhou, Zhejiang 310058, China
  3. Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China
  4. Institute of Ecology, College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing 100871, China
*Corresponding authors: Dr. Junjie Lin and Dr. Biao Zhu
E-mail addresses:junjielin@sanxiau.edu.cn(J. Lin) and biaozhu@pku.edu.cn(B. Zhu)
Abstract: Global climate change is expected to increase the frequency of drought and heavy precipitation, which could create more frequent drying-rewetting cycles (DWC) in the soils. Although the DWC effects on soil organic carbon (SOC) decomposition has been widely studied, the effect of DWC and the subsequent legacy effect on the decomposition of different SOC pools is still unclear. We conducted a 128-d laboratory incubation to investigate the DWC effects by using soils from old-field for 15 years (OF, representing active SOC), bare-fallow for 15 years (BF), and bare-fallow for 23 years plus extra 815-d incubation (BF+, representing relatively resistant SOC). The experiment included nine 10-d DWC of three treatments: 1) one mean constant-moisture at 60% water-holding capacity (WHC), 2) a mild DWC with 10-d drying to 40% WHC and immediately rewetting to 80% WHC, and 3) a strong DWC with 10-d drying to 20% WHC and immediately rewetting to 100% WHC. Following the DWC period (0-90 d), there was a 10-d stabilization period (adjusting all treatments to 60% WHC), and then a 28-d extended incubation under the constant moisture of 60% WHC. During the DWC period, the strong DWC had a strong effect on CO2 release compared with the constant-moisture control, reducing the SOC decomposition from OF by 8% and BF by 10%, while increasing the SOC decomposition of BF+ by 16%. In addition, during the extended period, both mild and strong DWC significantly increased SOC mineralization of OF, but decreased that of BF and BF+. This legacy effect induced by DWC compensated the changes in CO2 release during the DWC period, resulting in the minor response of SOC decomposition of OF and BF+ to the DWC during the entire incubation. Together, DWC could create both direct and legacy effects, and these effects vary with DWC intensity and SOC pools.
Keywords : Drying-rewetting; Soil carbon pool; Soil organic matter; Soil respiration; Legacy effect
Abbreviations : DWC – drying-rewetting cycles; OF – old-field; BF – bare-fallow; BF+ – bare-fallow + incubation; C – carbon; CO2 – carbon dioxide; SOC – soil organic carbon; MBC – microbial biomass carbon; DOC – dissolved organic carbon; TC – total carbon; TN – total nitrogen; C/N – the ratio of carbon to nitrogen; F:B – the ratio of fungi to bacteria.