The direct and legacy effects of drying-rewetting cycles on active and
relatively resistant soil carbon decomposition
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 DWC effects on 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) constant-moisture at 60% WHC, 2) mild DWC with 10-d
drying to 40% WHC and rewetting to 80% WHC, and 3) strong DWC with
10-d drying to 20% WHC and rewetting to 100% WHC. Following DWC
period, there was a 10-d stabilization period (adjusting all treatments
to 60% WHC), and then a 28-d extended incubation. During DWC period,
the strong DWC had 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%.
During extended period, both mild and strong DWC significantly increased
SOC mineralization of OF, but decreased that of BF and BF+. This legacy
effect compensated the changes in CO2 release during DWC period,
resulting in the minor response of SOC decomposition of OF and BF+ to
the DWC during the entire incubation.