干旱区生态环境知识资源中心

Rainfall amounts and timing in addition to air temperature influence soil respiration (R-soil) especially in semi-arid ecosystems. However, information about R-soil in semi-arid floodplains and its response to natural rainfall events is particularly limited. In this study, we measured in situ R-soil monthly from July 2014 to August 2015 under eucalyptus canopies and intercanopy of a semi-arid floodplain woodland, adjacent to the River Murray, Australia. R-soil was greater under canopy than intercanopy. Five days of rainfall (total of 62 mm) in summer (air temperature approximately 23 degrees C) increased R-soil by 70-85% 4 days after the last rainfall event compared with that before the rainfall. The relative increase was similar under canopy and intercanopy. R-soil remained high over the following 2 months with no rain, although soil water content in the top soil was very low. This suggests that in the months following the short rain period, roots and rhizosphere (autotrophic respiration) in the moist subsoil were the major contributors to the total R-soil. On the other hand, a single rainfall event (51 mm) in autumn (air temperature approximately 17 degrees C) did not increase R-soil although top soil water content was 3 times higher than in the previous dry period. A laboratory incubation experiment showed that rewetting of dry soil induced only a brief flush of heterotrophic R-soil. This study emphasized the importance of quantifying R-soil in similar dry floodplains to better predict their role in the global carbon cycle, particularly in light of the predicted changes in rainfall patterns in many semi-arid regions.