4.2 Relationship of soil microbial characteristic and microbial
CUEC:N
Soil
microbial CUE can affect soil C cycling (Spohn et al. , 2016). We
found that NT increased the soil microbial CUEC:N on
average compared with CT (Fig. 2) because no-tillage can decrease soil
temperature by surface mulching and further increase microbial CUE
(Apple et al. , 2006; Wetterstedt & Agren, 2011). In addition,
higher residue production under NT is constantly supplying fresh and
labile organic substrates for microbial activity and biomass thus
explaining the greater CUE observed under NT compared with CT
(Álvaro-Fuentes et al. , 2013). Microbial CUEC:Nincreased with increasing N application under both tillage treatments
(Fig. 2). The reason is that N addition can reduce microbial
respiration metabolism (Liuet al. , 2018; Spohn et al. , 2016; Thiet et al. ,
2006) and increase microbial biomass (Jha et al. , 2020),
resulting in higher microbial CUEC:N.
Furthermore, although a recent study showed that microbial diversity
drives CUE in artificial soil (Domeignoz-Horta et al. , 2020), to
the best of our knowledge, few experimental studies have directly
demonstrated the interaction effect of tillage management and N
application on microbial CUE in a field experiment. In this study, the
PLS-PM showed that tillage and nitrogen influenced microbial
CUEC:N through the microbial diversity and community
structure (Fig. 9). We also found that the bacterial and fungal
diversity had different influences on microbial CUEC:N(Fig. 9) under two tillage and these relationships were regulated by N
application (Fig. S1) under no-tillage. Bacterial diversity positively
influenced microbial CUEC:N, whereas fungal diversity
had an adverse impact on microbial CUEC:N (Fig. 9). The
difference points to the importance of studying the diversity of fungal
and bacterial communities separately
for predicting soil C cycling.
In addition, microbial network
complexity driving carbon cycling with direct feedback effects on
multiple ecosystem functions (Morriën et al. , 2017; Wagg et
al. , 2019; Zhou et al. , 2010), which could also influence
microbial CUE. Further research should be undertaken to explore the
effect of bacterial and fungal networks on microbial
CUEC:N.