4.2. Legacy effects of DWC on soil carbon mineralization
Both 80-40% and 100-20% WHC treatments increased C mineralization in
OF soil but decreased it in BF and BF+ soils compared to the mean
constant-moisture control treatment during the extended period (Fig.
4b). This result indicated that the repeated DWC could cause a legacy
effect on soil C mineralization, and this legacy effect can last for at
least 38 d (including 10-d stabilization period and 28-d extended
period).
Butterly
et al.
(2011)
implied that this legacy effect can last for more than 35 d, and
Li et
al.
(2018)
believed that after 4 times of DWC, this legacy effect can last for at
least 60 d.
Compared to the mean constant-moisture treatment (60% WHC), the MBC
content at the start of the extended period (100 d) was higher in the
100-20% WHC treatment for OF soil (Fig. 5a), while was lower in both
80-40% and 100-20% WHC treatments for BF and BF+ soils (Fig. 5a).
Moreover, there was a positive correlation between MBC and cumulative C
mineralization during the extended period across the three soils (Fig.
6a). These results suggested that the changes in microbial biomass
affected the legacy effect of DWC on soil C mineralization.
Additionally, DOC was also positively correlated with cumulative C
mineralization during the extended period across the three soils (Fig.
6b), indicating that the amount of microbial biomass and labile
substrates (i.e. DOC) both contributed to the legacy effect of DWC on
soil C mineralization. Notably, the fact that both MBC and DOC were
positively correlated with cumulative C mineralization during the
extended period is likely due to the positive linear relationship
between MBC and DOC (Fig. S4). Moreover, the DWC-driven changes of soil
microbial community composition may also contribute to this legacy
during the extended period (Meisner et al., 2021). Together, these
results are consistent with the finding of
Li et
al.
(2018)
who showed that the legacy effect during the extended period is
attributed to the amount of plant litter (as substrate) and microbial
biomass.
Taking together, both mild and strong DWC treatments had a minor effect
on SOC decomposition in OF and BF+ soils, respectively, but decreased
SOC decomposition in BF soil by 12% and 14%, respectively (Fig. 4c).
However, it should be noted that these results need to be interpreted
with caution, because we did not measure the C release during the
stabilization period (90-100 d) and the extended period (100-128 d, 28
days) may not be long enough. Future studies can use a longer extended
period and measure microbial community composition for a more
mechanistic understanding of the legacy effect of DWC on soil C release.