3.2 Effects of grassland conversion on soil microbes
Conversion of grassland to cropland significantly decreased the soil
total microbial biomass by 14%, Gram+ bacteria biomass by 19%, Gram-
bacteria biomass by 22%, fungal biomass by 24%, actinomycete biomass
by 17% and AMF biomass by 34%. Grassland conversion also significantly
reduced the relative abundance of bacterial and fungal FLFAs and F:B
ratio at surface 0-10cm soil (Figure 2A, B, C). In terms of soil
functional composition, Gram+ and Gram- bacteria are the most abundant
groups (Figure 2D).
The difference in soil microbial biomass between grassland and cropland
varied with soil depth (Table 2); in the 0-10-cm and 10–20-cm soil
layers, the cropland had lower soil microbial biomass at the various
sites (P <0.01, Table 2) but had higher soil microbial
biomass than grassland in the 20-30-cm soil layer
(P <0.05, Table 2). For each soil layer, the differences
in Gram+, Gram-, Fungi, Act and AMF between the cropland and grassland
showed patterns similar to that of total microbial biomass (Table 2).
The site (S), land use (LU) and soil depth (SD) significantly affected
the soil microbial biomass (Table 3). There was no statistically
significant interactions between S and the others factors (LU and SD) (P
> 0.05), while LU and SD exist significant effect on soil
microbial biomass (Table 3, P <0.05). Moreover, the
correlation analysis showed that soil C and N were positively correlated
with biomass of most lipid categories associated with bacteria, fungi
and actinomycetes, while other soil parameters including pH, SM,
NH4+,
NO3- and aggregations had no effects
on those variables (Table 4).