4.3 The influence of microbial CUEC:N on soil POC
and MAOC fractions
POC is a functional soil component for persistent soil organic carbon
(Witzgall et al. , 2021). In contrast to POC, MAOC is more
physically or chemically protected, which makes it less vulnerable to
mineralization (Abramoff et al. , 2018). We found that high N
application (210 kg N
ha-1) increased POC and MAOC content under two tillage
practices (Fig. 9), which is similar to the previous study (Ye et
al. , 2018). The possible reason was that plant biomass (Stewartet al. , 2016; Thomas et al. , 2010; Wang et al. ,
2018) and microbial residues (Chen et al. ,
2020a)
increased with increasing N application. However, some discrepant
findings showed that N addition decreased (Ye et al. , 2018) or
had no significant influence on MAOC (Yuan et al. , 2020). The
main reason for the inconsistent results could be that microbial
residues controlled the changes of soil MAOC pool under N addition and
the microbial residues were different due to different N application
rates among these studies (Averill & Waring, 2018; Chen et al. ,
2020a; Su et al. , 2020; Yang et al. , 2020b).
We further found that the CUEC:Nwas significantly positively correlated with POC and MAOC and the
increase rates were higher under NT than CT, which was influenced
by nitrogen application (Fig. S2). Moreover, the POC also had a
positive effect on MAOC (Fig. 9) because a portion of POC was degraded
by microbes and then formed part of the MAOC (Su et al. , 2020).
Therefore, these results highlight that nitrogen regulates the influence
of microbial CUEC:N on soil organic carbon fractions
under tillage practices.