Abstract
Tillage practices can influence soil microbial
carbon
use efficiency (CUE), which is critical for carbon cycling in
terrestrial ecosystems. The effect of tillage practices could also be
regulated by nitrogen (N) addition. However, the soil microbial
mechanism about N fertilizer effect on microbial CUE under no-tillage is
still unclear. We investigated how N fertilizer regulates the effect of
tillage management on microbial CUE through changing microbial
properties and further assessed the impact of microbial CUE on
particulate (POC) and
mineral-associated organic matter carbon (MAOC) using a
16-yr field experiment with
no-tillage (NT) and conventional tillage (CT), both of which combined
with 105 (N1), 180 (N2), and 210 kg N ha-1 (N3) N
application.
We
found that microbial CUE increased with increasing N application rate.
NT increased microbial CUE compared with CT under N1. The bacterial and
fungal diversities of NT was higher than CT and N application decreased
their diversities in the 0-10 cm
layer.
The partial least squares path model showed that bacteria diversity,
fungal diversity, and fungal community structure played more critical
roles in increasing microbial CUE. Furthermore, POC and MAOC under NT
were higher than CT and they also increased with increasing N
application rate. This could be explained by the finding that increasing
microbial CUE induced by N application had the potential to increase POC
and MAOC. Overall, N addition is an important pathway to influence
microbial CUE, which is mainly regulated by bacterial
and fungal diversities rather than their biomass under no-tillage.