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Title:   Author  item
                                            WANG, JUN - Xian Universityitem
                                            QUAN-QUAN, LIU - Xian Universityitem
                                            RONG-RONG, CHEN - Xian Universityitem
                                            WEN-ZHAO, LIU - Xian Universityitem
                                            Sainju, Upendra
  Submitted to: Applied Soil Ecology
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 9/1/2015
                                    Publication  Date: 9/16/2015
                                    Publication URL: http://handle.nal.usda.gov/10113/61598Citation: Wang, J., Quanquan, L., Rong-Rong, C., Wen-Zhao, L., Sainju, U.M. 2015. Soil carbon dioxide emissions in response to precipitation frequency in the Loess Plateau, China. Applied Soil Ecology. 96:288–295. doi:10.1016/j.apsoil.2015.08.026.Interpretive Summary: Precipitation controls ecosystem processes in the arid and semiarid regions and stimulate soil CO2 emissions, so-called the “Birch Effect”, by enhancing microbial activity and mineralization of organic matter due to increased soil water content. As extreme precipitation events and severe droughts are predicted in the future due to global climate change, changes in precipitation pattern may have significant influence on carbon dioxide (CO2) emissions and soil carbon (C) storage. Little is known about the effect of precipitation frequency and mechanisms responsible for this effect in dryland cropping systems. 

We evaluated the effect of three precipitation frequencies (5-, 10-, and 20-d intervals [I5, I10, and I20, respectively]) on soil CO2 fluxes for 60 days during fallow and soil chloroform-fumigated (CFE) and nonfumigated (EOC) C and microbial biomass C (MBC) in the Loess Plateau of China. 

The CO2 flux increased immediately following precipitation events, with peak fluxes of 7.9, 8.2, and 7.7 μmol CO2 m-2 s-1 for I5, I10, and I20, respectively. Cumulative CO2 flux from 55 to 60 d was greater for I5 and I10 than I20. Soil C fractions were not affected by precipitation simulation at the first event, but CFE and MBC increased from the first to the last precipitation event, especially for I5 and I10. The CO2 flux was strongly correlated with CFE and EOC at the first event, but the correlation decreased from the first to the last event for I10 and I20. In contrast, the correlation of CO2 flux with MBC increased. 

Greater precipitation frequency at shorter precipitation intervals increased CO2 emissions more than longer intervals due to increased soil water content. The dominant mechanism for the “Birch Effect” shifted from “substrate supply” at the first precipitation event to “microbial stress” at the last event, especially for shorter precipitation intervals.
                                Technical Abstract: Precipitation events can induce episodic CO2 emissions, so called the “Birch Effect”, but how precipitation frequency influences the mechanisms responsible for this effect in dryland cropping systems is not well known. We evaluated the effect of three precipitation frequencies (5-, 10-, and 20-d intervals [I5, I10, and I20, respectively]) on soil CO2 fluxes for 60 days during fallow and soil chloroform-fumigated (CFE) and nonfumigated (EOC) C and microbial biomass C (MBC) in the Loess Plateau of China. The CO2 flux increased immediately following precipitation events, with peak fluxes of 7.9, 8.2, and 7.7 μmol CO2 m-2 s-1 for I5, I10, and I20, respectively. Cumulative CO2 flux from 55 to 60 d was greater for I5 and I10 than I20. Soil C fractions were not affected by precipitation simulation at the first event, but CFE and MBC increased from the first to the last precipitation event, especially for I5 and I10. The CO2 flux was strongly correlated with CFE and EOC at the first event, but the correlation decreased from the first to the last event for I10 and I20. In contrast, the correlation of CO2 flux with MBC increased. Greater precipitation frequency at shorter precipitation intervals increased CO2 emissions than longer intervals due to increased soil water content. The dominant mechanism for the “Birch Effect” shifted from “substrate supply” at the first precipitation event to “microbial stress” at the last event, especially for shorter precipitation intervals.


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