Soil carbon dioxide emissions in response to precipitation frequency in the Loess Plateau, China

摘要

Precipitation events can induce episodic CO2 emissions, so called the "Birch Effect", which could be affected by soil microbial activity in dryland cropping systems. Our objective was to evaluate the effect of precipitation frequencies on soil CO2 fluxes and the mechanism responsible for the Birch Effect during fallow after winter wheat harvest in the Loess Plateau of China. A simulated precipitation of 240 mm was applied at 5, 10, and 20 days intervals (I5, I10, and I20, respectively) for 60 days and soil CO2 flux, K2SO4-extractable C (EOC) and microbial biomass C (MBC) were measured. The CO2 flux increased immediately following precipitation events, with peak fluxes of 7.9, 8.2, and 7.7 mu mol CO(2)m(-2) s(-1) for I5, I10, and I20, respectively. Cumulative CO2 flux from days 55-60 was greater for I5 and I10 than I20. The EOC and MBC were not affected by precipitation simulation at the first event, but MBC increased from the first to the last precipitation event, especially for I5 and I10. The CO2 flux was strongly correlated with EOC at the first event (r = 0.73, 0.85 and 0.90 for I5, I10 and I20, P 0.01, respectively), but not correlated with EOC at the last event for I5 and I10 and the correlation decreased from the first to the last event (r = 0.47, P 0.01) for I20. In contrast, the correlation coefficient of CO2 flux with MBC was not significant at first event and increased to 0.81 (P 0.01), 0.44 and 0.47 (P 0.05) at the last event for I5, I10 and I20, respectively. Higher precipitation frequency at shorter intervals increased CO2 emissions compared to lower frequency at longer intervals due to enhanced microbial activity as a result of increased substrate availability from accelerated soil aggregate destruction. 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. (C) 2015 Elsevier B.V. All rights reserved.